Network Layer,
Redirect data gram for the type of service and host
Type 5 code 3 points to a better route to the destination host using the desired TOS level
Router redirect
Type 5 codes 0-3
ARP Stack
- sits at the top of the Link Layer - asks node with target IP to identify itself - uses broadcast to reach all nodes
Subnets & Aggregation
- subnets: internally split up one prefix - aggregation: externally join multiple separate IP prefixes
IPv6 transition: IPv4 tunnelling
- tunnel through IPv4 network - IPv6 packet wrapped in IPv4 packet - difficulty is setting up tunnel endpoints and routing
DHCP Messages: Bootstrap
--> Discover <-- Offer --> Request <-- ACK
DHCP Messages: Renew
--> Request <-- ACK
Binary unmasked bit
0
Private or public 23.234.67.10/8
Public IP Address
Private or public 172.15.54.41/16
Public IP address
Code 1-8
0 = Net Unreachable 1 = Host Unreachable 2 = Protocol Unreachable 3 = Port Unreachable 4 = Fragmentation Needed 5 = Source Route Failed 6 = Destination Net Unknown 7 = Destination Host Unknown 8 = Source Host Isolated
what 3 things is the routing table used for?
1. Determine where the packet wants to go 2. the router reads the first field in the IP header which is the Destination Address 3. It looks in the Net field of its routing table for a match
What are the 3 ways a route can be placed in a routing table?
1. Direct Connection 2. Manually configure 3. Dynamically by using a routing protocol
What are the 2 primary routing protocols?
1. Distance vector 2. Link-state
What are the 5 types of ICMP messages
1. Echo Request/Reply 2. Destination Unreachable 3. Time Exceeded 4. Redirect 5. Router Discovery
What does a ICMP Echo Request packet consist of?
1. Ethernet header 2. IP header 3. ICMP header 4. Undefined data
What are the routing protocols used to connect these routing domains knows as?
Exterior Gateway Protocols (EGP)
Command: netstat -r
Linux and Windows
What form do ICMP messages take?
Specially Formatted IP datagrams with specific associated message types and codes
Netmask on routing list
Lists a subnet mask that informs the host how to determine the network and the host portions of the IP address.
IPv4 Route Table
Lists all known IPv4 routes, including direct connections, local network, and local default routes.
IPv6 Route Table
Lists all known IPv6 routes, including direct connections, local network, and local default routes.
BGP route selection
# Router may learn about more than one route to destination AS. Router must select route. # Route selection rules: 1. local preference value attribute: policy decision 2. shortest AS-PATH 3. closest NEXT-HOP router: hot potato routing 4. additional criteria
Transition from IPv4 to IPv6
# not all routers can be upgraded simultaneously * no "flag days" * how will network operate with mixed IPv4 and IPv6 routers? # tunneling: IPv6 datagram carried as payload in IPv4 datagram among IPv4 routers
OpenFlow protocol
# operates between controller, switch # TCP used to exchange messages * optional encryption # three classes of OpenFlow messages: * controller-to-switch * asynchronous (switch to controller) * symmetric (misc)
What does the TTL determine?
How many routers the request can jump too.
Packet Size: Problem
- how do we connect networks with different sized packets? - split up? - discover largest size to use?
NAT: how it works
- internal/external table - usually combines IP:port -- internal IP and external IP -- too few IPs; ports allows for 1-1 matching
:used for small networks, especially those with less than 250 hosts :1st 3bytes-network address + last byte-the host address :1st 3 bits of 1st byte: 1 1 0 + reminder bits; 0s,1s :all network 192-223
Class C IP address
IP addressing: introduction
# IP address: 32-bit identifier for host, router interface # interface: connection between host/router and physical link * router's typically have multiple interfaces * host typically has one or two interfaces (e.g., wired Ethernet, wireless 802.11) # IP addresses associated with each interface！！！！！！！！！！！！
OSPF (Open Shortest Path First)
# "open": publicly available # uses link-state algorithm * link state packet dissemination * topology map at each node * route computation using Dijkstra's algorithm # router floods OSPF link-state advertisements to all other routers in entire AS * carried in OSPF messages directly over IP (rather than TCP or UDP * link state: for each attached link # hierarchical OSPF in large domains (see next slide) # IS-IS routing protocol: nearly identical to OSPF
Internet inter-AS routing: BGP
# BGP (Border Gateway Protocol): the de facto inter-domain routing protocol * "glue that holds the Internet together" # BGP provides each AS a means to: * eBGP: obtain subnet reachability information from neighboring ASes不同as之间 * iBGP: propagate reachability information to all ASinternal routers.同一个as之间 * determine "good" routes to other networks based on reachability information and policy # allows subnet to advertise its existence to rest of Internet: "I am here"
BGP basics
# BGP session: two BGP routers ("peers") exchange BGP messages over semi-permanent TCP connection: * advertising paths to different destination network prefixes (BGP is a "path vector" protocol) # when AS3 gateway router 3a advertises path AS3,X to AS2 gateway router 2c: * AS3 promises to AS2 it will forward datagrams towards X
IPv6: adoption
# Google: 8% of clients access services via IPv6 # NIST: 1/3 of all US government domains are IPv6 capable
how does an ISP get block of addresses?
# ICANN: Internet Corporation for Assigned Names and Numbers http://www.icann.org/ * allocates addresses * manages DNS * assigns domain names, resolves disputes
Problems with NAT
Makes P2P connections complicated if one of Peer A or Peer B is behind a NAT since the server cannot accept TCP connections for the peer.
Path attributes and BGP routes
# advertised prefix includes BGP attributes * prefix + attributes = "route" # two important attributes: * AS-PATH: list of ASes through which prefix advertisement has passed * NEXT-HOP: indicates specific internal-AS router to nexthop AS # Policy-based routing: * gateway receiving route advertisement uses import policy to accept/decline path (e.g., never route through AS Y). * AS policy also determines whether to advertise path to other other neighboring ASes
Internet approach to scalable routing
# aggregate routers into regions known as "autonomous systems" (AS) (a.k.a. "domains") # intra-AS routing * routing among hosts, routers in same AS ("network") * all routers in AS must run same intra-domain protocol * routers in different AS can run different intra-domain routing protocol * gateway router: at "edge" of its own AS, has link(s) to router(s) in other AS'es # inter-AS routing * routing among AS'es * gateways perform interdomain routing (as well as intra-domain routing)
Intra-AS Routing
# also known as interior gateway protocols (IGP) # most common intra-AS routing protocols: * RIP: Routing Information Protocol * OSPF: Open Shortest Path First (IS-IS protocol essentially same as OSPF) * IGRP: Interior Gateway Routing Protocol (Cisco proprietary for decades, until 2016)
Output ports
# buffering required when datagrams arrive from fabric faster than the transmission rate * Datagram (packets) can be lost due to congestion, lack of buffers # scheduling discipline chooses among queued datagrams for transmission * Priority scheduling - who gets best performance, network neutrality
Output port queueing
# buffering when arrival rate via switch exceeds output line speed # queueing (delay) and loss due to output port buffer overflow!
Other changes from IPv4
# checksum: removed entirely to reduce processing time at each hop # options: allowed, but outside of header, indicated by "Next Header" field # ICMPv6: new version of ICMP * additional message types, e.g. "Packet Too Big" * multicast group management functions
Switching via a bus
# datagram from input port memory to output port memory via a shared bus # bus contention: switching speed limited by bus bandwidth # 32 Gbps bus, Cisco 5600: sufficient speed for access and enterprise routers
Input port queuing
# fabric slower than input ports combined -> queueing may occur at input queues * queueing delay and loss due to input buffer overflow! # Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward
OpenFlow data plane abstraction
# flow: defined by header fields # generalized forwarding: simple packet-handling rules * Pattern: match values in packet header fields * Actions: for matched packet: drop, forward, modify, matched packet or send matched packet to controller * Priority: disambiguate overlapping patterns * Counters: #bytes and #packets
Interconnected ASes
# forwarding table configured by both intraand inter-AS routing algorithm * intra-AS routing determine entries for destinations within AS * inter-AS & intra-AS determine entries for external destinations
network-layer functions
# forwarding: move packets from router's input to appropriate router output # routing: determine route taken by packets from source to destination * routing algorithms
DHCP: Dynamic Host Configuration Protocol
# goal: allow host to dynamically obtain its IP address from network server when it joins network * can renew its lease on address in use * allows reuse of addresses (only hold address while connected/"on") * support for mobile users who want to join network (more shortly) # DHCP overview: * host broadcasts "DHCP discover" msg [optional] * DHCP server responds with "DHCP offer" msg [optional] * host requests IP address: "DHCP request" msg * DHCP server sends address: "DHCP ack" msg # DHCP can return more than just allocated IP address on subnet: * address of first-hop router for client * name and IP address of DNS sever * network mask (indicating network versus host portion of address)
How does a host get IP address?
# hard-coded by system admin in a file * Windows: control-panel->network->configuration- >tcp/ip->properties * UNIX: /etc/rc.config # DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server * "plug-and-play
IPv6: motivation
# initial motivation: 32-bit address space soon to be completely allocated. # additional motivation: * header format helps speed processing/forwarding * header changes to facilitate QoS IPv6 datagram format: * fixed-length 40 byte header * no fragmentation allowed
Data plane
# local, per-router function # determines how datagram arriving on router input port is forwarded to router output port # forwarding function
OpenFlow abstraction
# match+action: unifies different kinds of devices # Router * match: longest destination IP prefix * action: forward out a link # Switch * match: destination MAC address * action: forward or flood # Firewall * match: IP addresses and TCP/UDP port numbers * action: permit or deny # NAT * match: IP address and port * action: rewrite address and port
NAT: network address translation
# motivation: local network uses just one IP address as far as outside world is concerned: * range of addresses not needed from ISP: just one IP address for all devices * can change addresses of devices in local network without notifying outside world * can change ISP without changing addresses of devices in local network * devices inside local net not explicitly addressable, visible by outside world (a security plus)
IP fragmentation, reassembly
# network links have MTU (max.transfer size) - largest possible link-level frame * different link types, different MTUs # large IP datagram divided ("fragmented") within net * one datagram becomes several datagrams * "reassembled" only at final destination * IP header bits used to identify, order related fragments
Control plane
# network-wide logic # determines how datagram is routed among routers along end-end path from source host to destination host # two control-plane approaches: * traditional routing algorithms: implemented in routers * software-defined networking (SDN): implemented in (remote) servers
MTU
Maximum Transmission Unit
Switching via interconnection network
# overcome bus bandwidth limitations # banyan networks, crossbar, other interconnection nets initially developed to connect processors in multiprocessor # advanced design: fragmenting datagram into fixed length cells, switch cells through the fabric. # Cisco 12000: switches 60 Gbps through the interconnection network
Why different Intra-, Inter-AS routing ?
# policy: * inter-AS: admin wants control over how its traffic routed, who routes through its net. * intra-AS: single admin, so no policy decisions needed # scale: * hierarchical routing saves table size, reduced update traffic # performance: * intra-AS: can focus on performance * inter-AS: policy may dominate over performance
Switching fabrics
# transfer packet from input buffer to appropriate output buffer # switching rate: rate at which packets can be transferred from inputs to outputs * often measured as multiple of input/output line rate * N inputs: switching rate N times line rate desirable # three types of switching fabrics
Network layer
# transport segment from sending to receiving host # on sending side encapsulates segments into datagrams # on receiving side, delivers segments to transport layer # network layer protocols in every host, router # router examines header fields in all IP datagrams passing through it
SDN: control/data plane interaction example
(1)S1, experiencing link failure using OpenFlow port status message to notify controller (2)SDN controller receives OpenFlow message, updates link status info (3)Dijkstra's routing algorithm application has previously registered to be called when ever link status changes. It is called. (4)Dijkstra's routing algorithm access network graph info, link state info in controller, computes new routes (5)link state routing app interacts with flow-table-computation component in SDN controller, which computes new flow tables needed (6)Controller uses OpenFlow to install new tables in switches that need updating
Communication with Destination Host is Prohibited Administratively
(Code = 10) - sent by a router that's configured to block access to the destination host
Communication with Destination Network is Prohibited Administratively
(Code = 9) - sent by a router that's configured to block access to the destination network
Communication Administratively Prohibited
(Type = 3, Code = 13) - a filtering policy prohibits forwarding the packet
Fragmentation Needed and DF Was Set
(Type = 3, Code = 4) - sent when a router needs to fragment a packet but can't
Source Route Failed
(Type = 3, Code = 5) - sent by a router that can't use strict or loose source routing path specified
IPv6: address size
- 128 bits - 8 groups of 4 hex digits - omit leading zeros, groups of zeros
IPv4: address length
- 32 bits - dotted quad notation: four 8-bit numbers separated by dots
What are some characteristics of the network service model?
- Guaranteed Delivery: Packet will eventually arrive at its destination - Guaranteed Delivery with bounded delay: Packet will arrive at its destination within a certain time frame - In-order Packet Delivery: Packets will arrive in the order they were sent - Guaranteed minimal bandwidth - Guaranteed maximum jitter: The time between the transmission of two successive packets is nearly equal / equal to their receipt at the destination. - Security Services
IP Forwarding
- IP addresses on one network belong to the same prefix
IP: Traceroute
- IP header contains TTL field - decremented every router hop - sends ICMP error if his zero - identifies routers on the path
Routing: scaling techniques
- IP prefixes: route to block of hosts - Network hierarchy: route to network regions - IP prefix aggregation: combine, and split, prefixes
Problems with IPv6
- Large 2^64 subnets potentially takes years to scan - If attacker Trudy gains access to subnet, she can identify other hosts on the local subnet - IPSec is overly complex / overengineered can hinder IPv6 security if used - MitM attack - IPv4 only nodes will be unable to handle IPv6 node features (ICMPv6, IPv6 packets)
List some methods to transition from IPv4 to IPv6
- Shutdown the entire internet and change all IPv4 notes to IPv6: NOT VIABLE - Dual Stack Approach: Create nodes that support both IPv4 and IPv6 - Tunneling: If there are IPv4 routers between IPv6 routers, encapsulate the IPv6 datagram into a IPv4 datagram, then extract it back upon receiving the IPv6 datagram
ICMP Message Format
- Type, Code, Checksum - carried in an IP packet
IP address/length notation
- address is lowest address in prefix - length is prefix bits
IP Prefixes
- addresses allocated in blocks called prefixes - addresses in an L-bit prefix have the same top L bits - there are 2^(32-L) addresses aligned on the 2^(32-L) boundary
NAT: box
- connects an internal network to an external network - many hosts connected using few external addresses - motivated by IP address scarcity
Routing Algorithms: goals
- correct - efficient - fair - fast convergence - scalability
Network Service Models
- datagrams / connectionless - virtual circuits / connection oriented
Routing Algorithms: rules
- decentralised, distributed setting - all nodes alike/equal - nodes information gleaned from neighbours - nodes operate concurrently - node/message/link failures possible
MTU: path to discovery
- discover MTU that will fit (avoid router fragmentation) - host tests path with large packet - routers provide feedback with size that would fit
Packet Size: Solutions
- fragmentation: split up large packets in the network - discovery: find the largest packet that fits on the network path and use it
Datagram Model: forwarding table
- gives next hop for each destination - may change
about IPv4
- length of IPv4 is variable; not all fields need to change - fields are measured in terms of 32-bit words - Shortest IPv4 header: 20 bytes + IP Header Length (IHL) would be 5; 20*8/32=5 -header is followed by variable data field that is a multiple of 8 bits with a maximum length of 65,535 octets
Prefix Specificity
- more specific (long prefix): fewer addresses - less specific (short prefix): longer addresses
DHCP Bootstrap
- node broadcasts message to network - message is all 1s (bits)
Datagram Model: how it works
- packet contains final address - each router uses this to forward packet to next step - each packet may take a different route
Virtual Circuit Model: how it works
- packet contains short label identifying circuit - label is unique for link (and temporary) - packets all follow the same route - each routers has a forwarding table keyed by circuit
ICMP: error reporting
- router encounters error while forwarding - send ICMP error report to IP source address - discards problematic packet - host needs to rectify
Host vs. Router
- routers do the routing and know all the ways to the destination - Hosts send remote traffic (out of prefix) to nearest router
Store and Forward Packet Switching
- routers receive complete packet - stores temporarily (if necessary) before forwarding
IPv4: Fragmentation
- sending router fragments the packet - receiving host reassembles the packet
Binary masked bit
1
Unicast
1 to 1 IP communications
Virtual Circuit Model
1) connection establishment - circuit set up - path is chosen - circuit info stored in routers 2) data transfer - packets forwarded along the path 3) Connection teardown - circuit information removed from servers Statistical sharing of links/no bandwidth needs to be reserved
Class A IPv4
1-126
What parameters are available with TraceRoute (cmd letters)
1. -d : Which instructs TR to not perform a DNS reverse query on the routers 2. -h max_hops: Where max_hops defeines the Max TTL to user 3. -w timeout: Timeout indicates how long to wait for a reply before displaying an asterick
Name 3 aspects of a VC Network
1. A path between source and destination hosts 2. VC numbers where each link is given a number 3. Entries in the forwarding table in each router
What do ICMP Router Advertisements do?
1. Configurations to send periodic ICMP Router Advertisement packets 2. They allow hosts to passivly learn about variable routes
Four steps of DHCP (hint: DORA)
1. DHCP Discover Message - Client connects to DHCP server by sending an encapsulated UDP packet containing destination address 255.255.255.255 and source IP address 0.0.0.0 which is passed to the link layer. 2. DHCP Offer Message - DHCP sends offer message upon receiving discover message containing proposed IP address for client, network mask, and IP address lease time (how long IP address will be valid) 3. DHCP Request Message - Client will receive several server offers and respond with this message that echoes back config parameters 4. DHCP ACK - Server responds to DHCP request with ACK message confirming requested parameters
What is MTU?
Maximum Transmission Unit is the maximum amount of data that a link-layer frame can carry
Describe the process of forwarding packets from Host A to Host B
1. Host A takes segments from transport layer and encapsulates each segment into a datagram 2. Datagrams are sent to its nearby router R1 3. Host B's nearby router R2 receives the datagrams 4. R2 extracts the transport layer segments from the datagrams and delivers the segments up to the Transport Layer of Host B
Three components of Internet's network layer
1. IP (Internet Protocol) 2. Routing protocol 3. ICMP (Internet Control Message Protocol)
What does a PING packet contain?
1. Identifier field set to 256 2. first echo sent the sequence number value is set to a multiple of 256 3. datafield contains the value = "abcdefghijklmnopqrstuvwabcdefghi"
What are the 3 types of routing operations BGP offers?
1. Inter-autonomous system routing 2. Intra-autonomous system routing 3. Pass-through autonomous system routing
what do routes consist of?
1. Network Address 2. Various metrics 3. vendor-specific information
What information does the ICMP layer provide?
1. Network Connectivity 2. Errors 3. Routing
What are 2 troubleshooting ways that can be used through ICMP
1. Ping 2. TraceRoute
what are the 2 most common IGPs ?
1. RIP (Version 1 and 2) 2. OSPF
Why don't packets just share the same VC number across each link?
1. Replacing the number from link to link decreases the size of the VC field in the packet header (since it can change the VC number to a smaller value) 2. Sharing the same VC number across all links can be very slow and complicated since each router would have to send messages to each other to agree on a common VC number. It's more efficient to have all links independently choose a VC number.
What are routing protocols used for?
1. Share information about the various networks on an internetwork 2. They are used to get packets through an internetwork
Distance Vector Protocols
1. Simplest Protocol 2. Uses end to end hop counts to compare routes
What else can the ICMP layer do?
1. Test network reachability 2. Discover the MTU 3. Discover routers or default gateways
How do Link-State Routing Protocoals differ from distance vector routing protocols?
1. They do not route by rumor 2. They do not periodically broadcast their entire table to all know routers
ICMP packets contain what 3 required fields after the IP header?
1. Type 2. Code 3. Checksum
What are the 2 versions of RIP
1. Version 1 : sends broadcast updates 2. Version 2 : supports non-default subnet masks, can send multicast updates
Message format
1.An ICMP message consist of a 8 byte header and a variable size data section 2.Each field in the message format of ICMP messages is defined as a).Common field for all message types b).Specific field for message types
Types of error handling messages
1.Destination unreachable 2.Source quench 3.Time exceeded 4.Parameter problems 5.Redirection
Types of query messages
1.Echo request and reply 2.Time stamp request and reply 3.Address mask request and reply 4.Router solicitation and reply
Types of ICMP messages
1.Error reporting messages 2.Query messages
Blackhole routers
May have icmp blocked for security reasons - providing no feedback
Error reporting
1.Error reporting messages are used to report problems that a router or a host encounters when it processes an IP packet 2.ICMP always reports error messages to the original source,because the only information available in the datagram about the route is the source and destination IP address 3.ICMP wont be used for correcting errors,it is simply used for reporting them
Query messages
1.ICMP is also used to diagnose some network problems,in addition to error reporting messages.This can be done by using query messages 2.A node sends a message that is answered in a specific format by the destination node 3.A query message is encapsulated in an IP packet,which in turn encapsulated in a data link layer frame
Introduction
1.ICMP stands for Internet Control Message Protocol 2.The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol suite. It is used by network devices, including routers, to send error messages and operational information indicating 3.ICMP is designed to compensate for the deficiencies of IP
Private IP Class a reserved addresses
10.0.0.0-10.255.255.255
loop back address
127.0.0.0/8
IPv6: address length
128 bits
IPV6 address size
128 bits, 340,282,366,920,938,463,463,374,607,431,768,211,456, or 340 undecillion addresses,
10000000
128 in binary
Class B IPv4
128-191
Private IP Class B reserved addresses
172.16.0.0-172.31.255.255
11000000
192 in binary
Class C IPv4
192-223
Private IP class C reserved addresses
192.168.0.0-192.168.255.255
@static length: all the subnets in the network use the same subnet mask @variable length: allows the subnets that make up the network to use different subnet masks - A small subnet with only a few hosts needs a subnet mask that accommodates only these hosts - A subnet with many hosts may need a different subnet mask to accommodate the hosts -** it is possible to define adequate hosts for each subnet by changing the subnet mask for each network ** Routing protocols RIP version 2 and OSPF support both
2 types of subnetting
Interface List
Lists the Media Access Control (MAC) address and assigned interface number of every network-capable interface on the host including Ethernet, Wi-Fi, and Bluetooth adapters.
11100000
224 in binary
Class D
224-239 used for multicast testing
11110000
240 in binary
Class E
240-255, reserved for future use
11111000
248 in binary
11111100
252 in binary
11111110
254 in binary
Default subnet mask for Class A
255.0.0.0
Default subnet mast for Class B
255.255.0.0
Default subnet mast for class C
255.255.255.0
-Expedited Forwarding PHB; -Assured Forwarding PHB -Default PHB
3 PHBs have been defined by the IETF:
IPv4 packet address
32 bit address on each packet
How many bytes of data is an ICMP Echo request
32 bytes
IPV4 address size
32-bit, 4,294,967,296 unique addresses, Of these, only 3.7 billion addresses are assignable
32 bits
4 sets of 8 bits make up an IP address
classes A, B, C, D, E
5 classes of IP addresses:
What port number does RIP based routers send and receive on?
520
What is the original RFC?
792
Code 9-15
9 = Communication with the destination network is Administratively prohibited 10 = Communication with the destination Host is Administratively prohibited 11 = Destination Net Unreachable for type of service 12 = Destination Host unreachable for Ype of Service 13 = Communication Admin Prohibited 14 = Host Precedence Violation 15 = Precedence cutoff in effect
0.0.0.0
A basic statement allowing IP addresses that do not match the network or routing table to go to the default gateway
Logically centralized control plane
A distinct (typically remote) controller interacts with local control agents (CAs)
Destination Unreachable
A family of messages - sent by a TCP/IP host that encounters a network configuration or service failure Addresses a variety of situations in which a packet becomes undeliverable (Type = 3, Code = 0-15) Provide useful feedback about packet delivery/security issues - used widely by techs and security personnel Can be used by attackers - to determine live hosts and ports that are left open on the network
Define forwarding table
A forwarding table, present in all routers, is used to index the header value of a packet which determines the router's outgoing link interface to which that packet is to be forwarded.
Packet
A piece of a message transmitted over a packet-switching network. See under packet switching
How a router works?
A router uses the information in the routing table to determine the best path to reach those destinations.
Internet routing table expansion
A routing table is used by routers to make best path determinations. As the number of servers (nodes) connected to the Internet increases, so too does the number of network routes. hese IPv4 routes consume a great deal of memory and processor resources on Internet routers.
received Reply
A successfully _________ indicates that packets can be delivered to the destination host and back
ARP
Address Resolution Protocol
the network layer uses four basic processes:
Addressing end devices Encapsulation Routing De-encapsulation.
When is the process guaranteed to converge in distance vector routing (regarding metrics)?
All nodes minimise same metric, this metric increases around loops
Enablepmtubhdetect
Allows for detecting routers that discard packets without sending notifications
Route Tracing
Allows for mapping a path between two hosts - with L3 devices' traversed along the path displayed
Interface on routing list
Lists the address of the physical interface used to send the packet to the gateway that is used to reach the network destination.
The Vector Network converges more slowly than the Link-State Network
True
constant and variable
An ICMP header includes a mandatory ________ portion and optional ___________ portion
:used for multicast groups :no network address <= multicast address are not location dependent (network address specifies the location of the network) :1st 4 bits of 1st byte: 1 1 1 0 :all network 224-239
Class D IP address
: reserved for future use : may never be used as a result of IPv6 -1st 5bits of 1st octet: 1 1 1 1 0; thus 1st octet starts from 240
Class E IP address
Classless IP addressing
Any network number can use any subnet mask.
Lack of end-to-end connectivity
However, because the public IP address is shared, the IP address of an internal network host is hidden. This can be problematic for technologies that require end-to-end connectivity.
:used for large networks :first byte-network address field + three bytes-the host address field :1st bit of 1st byte: 0 + next 7 bits; 0s,1s :all network 0-127
Class A IP address
:used for medium-sized networks :1st 2 bytes-network address field + 2nd 2 bytes-the host address :1st 2bits of 1st byte: 1 0 + next 14bits; 0s,1s :all network 128-191
Class B IP address
Class you would use for a small home network
Class C
:defined for customers who need reliable service from their ISPs even in times of network congestion -First 3 bits (bits 0, 1 and 2) define the priority class -Bits 3 and 4 specify the drop percentage -Bit 5 is always 0
Assured forwarding PHB
APIPA
Automatic Private IP addressing. is on the 169.254.0.0 network. occurs when a client cannot contact the DHCP server.
What are the different types of switches?
Backbone, edge, border, core, edge
Name three service models
Best Effort: Basically euphemism for "no service at all" ABR: Available Bit Rate: Average service CBR: Constant Bit Rate: Best service
advantages of IPv6 simplified header
Better routing efficiency for performance and forwarding-rate scalability No requirement for processing checksums Simplified and more efficient extension header mechanisms (as opposed to the IPv4 Options field) A Flow Label field for per-flow processing with no need to open the transport inner packet to identify the various traffic flows
192.168.10.255
Broadcast
What are the ways a node might send info to more than one destination?
Broadcast - send to all Multicast - send to all members of a group Anycast - send to any member of a group
CIDR
CIDR: Classless InterDomain Routing # subnet portion of address of arbitrary length # address format: a.b.c.d/x, where x is # bits insubnet portion of address
ISPs
Carriers
CIDR
Classless Interdomain Routing. States the number of masked bits in the subnet mask.
CIDR: /28
Classless inter-domain routing notation identifies how many total bits identify network mask
0x00
Code value for both ICMP Request and Reply
13
Communication Admin Blocked
Define Virtual Circuit Network (VC Networks)
Computer networks that only provide a connection service in the network layer
Define Datagram Networks
Computer networks that provide only connectionless service in the network layer
Edge router
Connect different AS's together
Define connection setup
Connection setup is how routers establish a connection between each other before packets can be sent.
The basic characteristics of IP are
Connectionless Best Effort (unreliable) Media Independent
what type of process is an ICMP Echo request?
Connectionless Process
Destination IP Address in IPv4
Contains a 32-bit binary value that represents the destination IP address of the packet.
Source IP Address in IPv4
Contains a 32-bit binary value that represents the source IP address of the packet.
Version in IPv4
Contains a 4-bit binary value identifying the IP packet version. For IPv4 packets, this field is always set to 0100.
Internet Header Length (IHL) in IPv4
Contains a 4-bit binary value identifying the number of 32-bit words in the header. The IHL value varies due to the Options and Padding fields. The minimum value for this field is 5 (i.e., 5×32 = 160 bits = 20 bytes) and the maximum value is 15 (i.e., 15×32 = 480 bits = 60 bytes).
Time-to-Live (TTL) in IPv4
Contains an 8-bit binary value that is used to limit the lifetime of a packet.It is specified in seconds but is commonly referred to as hop count.
Payload
Contains the Layer 4 segment information and the actual data.
DHCP Stack
DHCP UDP IP Ethernet
SDN perspective: data plane switches
Data plane switches # fast, simple, commodity switches implementing generalized dataplane forwarding (Section 4.4) in hardware # switch flow table computed, installed by controller # API for table-based switch control (e.g., OpenFlow) * defines what is controllable and what is not # protocol for communicating with controller (e.g., OpenFlow)
the best-effort service where a node tries to deliver as many packets with the default marking as soon as possible -codepoint is 000000
Default PHB
127.0.0.1
Default loopback address. used for testing only, cannot be configued as an ip address on a client.
What happens when the TTL value reaches zero?
Deletes the packet Optionally notify the sender that the packet was deleted
Source quench
Type 0x04 code 0x00
0
Destination Network Unreachable
3
Destination Unreachable
3
Destination Unreachable Host/Network
1
Destination host unreachable
What do packets contain?
Destination identifier, source identifier, payload (info about layers, about transport, application)
:DiffServ Code Point (DSCP); used to provide QoS -6bits :explicit congestion notification (ECN); used for flow control -last 2 bits
DiffServ field is subdivided into two parts:
The local table of the host typically contains:
Direct connection
Two types of routes found on a routing table
Directly-connected routes Remote routes
What algorithm can you use to compute the shortest paths between nodes in link state routing?
Djikstra
DHCP
Dynamic Host Configuration Protocol
Router solicitation
Type 10 code 0. A host has no default gateway and may send icmp solicitation at boot
In link state routing, how does every node knows the topology (map) of the whole network?
Each node floods its local link state - on receiving a new LS message, routers forward the message to all its neighbours apart from the one it received the message from. Can now find the shortst path.
Link state routing
Each node maintains its local link state - a list of its directly attached links and their costs. Each node forwards info it knows onto next nodes it didn't receive data from.
hop
Each route the packet takes to reach the destination host
Generalized Forwarding and SDN
Each router contains a flow table that is computed and distributed by a logically centralized routing controller
8
Echo
0
Echo Reply Packet
0 -> 8
Echo Reply from Echo Request
8
Echo request Packet
Enablepmtudiscovery
Enables or disables pmtu discovery on the host
what does EIGRP stand for?
Enhanced Interior Gateway Routing Protocol
What does the Checksum field provide?
Error detection for the ICMP header
What is the mathematical principle behind distance vector routing?
Eventually ask nodes will converge to the same route if nodes keep making updates
Distance vector routing
Every node can talk to its immediate neighbours, providing updates about the "whole" network to its neighbours
Define connection state information
Every time a connection is established or released, the forwarding table entry must be updated.
Consider a datagram that is 1500 bytes long that needs to travel through a network with MTU of 620 bytes (Assume no options used=the header is 20 bytes long + at most 600 bytes of the data can be accommodated in a packet) the original packet will be divided into three fragments: -Fragment 1 (offset 0) has 600 bytes; Fragment 1 (Offset 0/8 = 0) -Fragment 2 (offset 600) has 600 bytes; Fragment 2 (Offset 600/8 = 75) -Fragment 3 (offset 1200) has 300 bytes; Fragment 3 (Offset 1200/8 = 150) *Each fragment contains a header that duplicates most of the original header (20bytes in this case)
Example of MTU Practice
Describe IPv6 format
Expanded Addressing: Source and destination address increased from 32 to 128 bits Streamlined 40-byte header: Faster processing for each IP datagram Flow label and priority: Describes what kind of data will be sent (e.g. video treated as flow, emails not flow). This label specifications are still being discussed today. BIG DIFFERENCES: - No more fragmentation, packet is dropped if too large for the output link of the router - No more checksum since Transport Layer already handles this function - No more options field
describes a mechanism to build low-loss, low-delay, low-jitter, assured bandwidth E2E service within a particular DS domain : used for a traffic class that is required to be granted enough resources to ensure that it receives its minimum guaranteed rate : ex; voice :codepoint is 000010
Expedited Forwarding PHB
allows end-to-end notification of network congestion without dropping packets -00: indicates that the node is non-ECN capable, or non-ECN transport (Non-ECT) -01: ECN capable transport, ECT(0) -10: ECN capable transport, ECT(1) -11: Congestion encountered (CE)
Explicit Congestion Notification (ECN)
ICMP type numbers
ICMP type numbers
Differentiated Services (DS) in IPv4
Formerly called the Type of Service (ToS) field, the DS field is an 8-bit field used to determine the priority of each packet. The first 6 bits identify the Differentiated Services Code Point (DSCP) value that is used by a quality of service (QoS) mechanism. The last 2 bits identify the explicit congestion notification (ECN) value that can be used to prevent dropped packets during times of network congestion.
What do switches do?
Forward packets
Forwarding is carried out in the ... plane whilst routing is carried out in the .... plane?
Forwarding - data plane Routing - control plane
Driving Analogy for forwarding and routing
Forwarding is the process of getting through a single street while routing is the process of planning how to get from starting point to destination.
Difference between fowarding and routing
Forwarding is the transfer of a packet from an incoming link to an outgoing link within a SINGLE router. "Picking which output link to use from the given input" Routing involves ALL network routers that use routing protocols to determine the paths that packets take from source to destination. "Finding the overall path"
Imagine that you are a router and you receive a IP datagram that is larger than the output link's MTU. What do you do?
Fragment the data of the IP datagram into 2 smaller datagrams and send both of these smaller fragments to the output link.
In an IP router, does the software or hardware implement the data plane, where per-packet processing is carried out (implements what is in the routing table)?
Hardware
10
Host Admin Blocked
7
Host Unknown
Code 1
Host Unreachable
indicates the IP version number
IPv4 header-version 4bits
Why change from IPv4 to IPv6?
IPv4 is running out of available addresses. IPv6 addresses are increased from 32 to 128 bits.
Integrated security
IPv6 natively supports authentication and privacy capabilities.
Fields used in IPV4 Headings when a packet has to be fragmented due to MTU
Identification Flags Fragment Offset
IP Header
Identifies the packet characteristics.
Why is there an issue of there being an inconsistent link-state database in link state routing?
If a link goes down, some routers would know about failure before others - the shortest paths are therefore no longer consistent, causes loops
Parameter problem
If a router or the destination host discovers an ambiguous or missing value in the field of the datagram,it discards the datagram and sends the parameter message back to the source
Gateway on routing list
Lists the address used by the local computer to get to a remote network destination. If a destination is directly reachable, it will show as "on-link" in this column.
IPv4 packet has two parts
IP Header Payload
A remote host is determined by
IP address and subnet mask of the destination device.
Limitations of IPV4
IP address depletion Internet routing table expansion Lack of end-to-end connectivity
: the concept of networks and hosts (A host is any device on the network that can transmit and receive IP packets : IP address permits to be uniquely identified
IP addressing
ICMP
IP protocol for error and information messages (ping)
-Each byte of the address is represented by its decimal value and the different values are separated by dots in the form a.b.c.d -Valid IP addresses range from 0.0.0.0 to 255.255.255.255
IP version 4, IPv4, Addressing
used to define quality of service (QoS) for different network applications
IPv4 header-DSCP (Differentiated Services Code Point) 6bits
indicates the final destination of the packet
IPv4 header-Destination address 32bits
used to practice end-to-end notification of network congestion without dropping packets
IPv4 header-ECN (Explicit Congestion Notification) 2bits
:used to control or identify fragments :They are (in order, from most significant to least significant) -bit 0: Reserved and must be set to zero -bit 1: Don't Fragment (DF); f the DF flag is set, and fragmentation is required to route the packet, then the packet is dropped -bit 2: More Fragments (MF) : flags are used to fragment and reassemble packets *fragment(n)a part broken off; a small, detached portion; an imperfect part
IPv4 header-Flags 3bits
indicates where this fragment belongs in original packet; measured in 64-bit (or 8-byte) units : flags are used to fragment and reassemble packets
IPv4 header-Fragment Offset 13bits
used for error detection of the header
IPv4 header-Header Checksum 16bits
indicates packet header length in 32-bit words
IPv4 header-IHL (IP Header Length) 4bits
indicates which packet fragments belong together to avoid mismatch; it is incremented with each packet transmitted : flags are used to fragment and reassemble packets
IPv4 header-Identification 16bits
used to encode options requested by sender and is particularly used for source routing in which the IP addresses to visit are placed in the field. (Field may be empty)
IPv4 header-Options variable
used to ensure that packet header is a multiple of 32 bits
IPv4 header-Padding variable
indicates the higher-level protocol (TCP or UDP) should receive packet
IPv4 header-Protocol 8bits
indicates the originator of the packet
IPv4 header-Source address 32bits
indicates amount of time packet is allowed to stay in network
IPv4 header-Time to Live 8bits
specifies packet length in bytes of the header and data
IPv4 header-Total length 16bits
Gateway
Lists the address used by the local host to forward packets to a remote network destination. On-link indicates that the host is currently connected to it.
Roundabout Analogy for input ports, output ports, and switching fabric (Router Architecture)
Imagine a roundabout with an attendant at its entry station. The car arrives at the roundabout and the attendant looks up your final destination and tells you which roundabout exit to take. You then go through the roundabout and take the corresponding exit. Entry station is the input ports Roundabout is the switching fabric Roundabout Exit is the output ports
De-encapsulation
If the destination IP address within the header matches its own IP address, the IP header is removed from the packet. After the packet is de-encapsulated by the network layer, the resulting Layer 4 PDU is passed up to the appropriate service at the transport layer.
In connectionless the sender doesn't know?
If the receiver is present If the packet arrived If the receiver can read the packet
What is the problem with distance vector routing?
If use maximum capacity metric, cost doesn't change around loop - so might send back round due to link being max capacity and looping round. Routers might lie.
ICMP
Internet Control Message Protocol: Used with devices to communicate to each other. Ping is part of ICMP. Devices automatically use ping to ensure devices are connected.
Metric on routing list
Lists the cost of each route and is used to determine the best route to a destination.
Metric
Lists the cost of each route to a destination. Lower numbers indicate preferred routes.
What is difference between forwarding and routing in terms of routers communicating?
In forwarding, individual routers use the routing state to send packets on - has to happen whenever packets arrive. Whereas in routing, route is established already, packet only has to follow on that path.
History of IPV6
In the early 1990s, the Internet Engineering Task Force (IETF) grew concerned about the issues with IPv4 and began to look for a replacement
Improvements in IPV6
Increased address space Improved packet handling Eliminates the need for NAT Integrated security
Per-router control plane
Individual routing algorithm components in each and every router interact in the control plane
Name four components of a router
Input Ports: Performs the lookup function via forwarding table to determine which output port will be used for an incoming packet. Switching Fabric: Connects input ports to output ports Output Ports: Stores packets received from the switching fabric and transmits packets to output port Routing Processor: Executes routing protocols and maintains routing tables
What constitutes the data plane in a router?
Input linecards, interconnect fabric, output linecards
Describe how the forwarding table is setup when the address is 32-bits
Instead creating a forwarding table that's 2^32 entries, you can split the address into ranges. Look at the diagram below
3 sections of routing menu
Interface List IPv4 Route Table - Lists all known IPv4 routes, including direct connections, local network, and local default routes. IPv6 Route Table - Lists all known IPv6 routes, including direct connections, local network, and local default routes.
Define interface
Interface is the boundary between the host and its physical link. IP addresses are assigned to each interface. Since routers have multiple links, routers need multiple interfaces to use those links.
What are the routing protocols used inside a routing domain
Interior Gateway Protocols (IGP)
What are Exterior Gateway Protocols also known as?
Interior-Domain Routing Protocols
What are nterior Gateway protocols also know as?
Interior-Domain Routing Protocols
ICMP
Internet Control Message Protocol
What does ICMP stand for?
Internet Control Message Protocol
Redirect data gram for the network
Type 5 code 0 points to a better route to the destination network
The fields used to identify and validate the packet include:
Internet Header Length (IHL) eferred to as the Packet Length, this 16-bit field defines the entire packet (fragment) size, including header and data, in bytes. The minimum length packet is 20 bytes (20-byte header + 0 bytes data) and the maximum is 65,535 bytes. Header Checksum - The 16-bit field is used for error checking of the IP header. The checksum of the header is recalculated and compared to the value in the checksum field. If the values do not match, the packet is discarded.
IP
Internet Protocol
2 most common network layer protocols
Internet Protocol version 4 (IPv4) Internet Protocol version 6 (IPv6)
IF
Lists the interface numbers from the Interface List section of the netstat -r command. The interface numbers correspond to the network capable interface on the host, including Ethernet, Wi-Fi, and Bluetooth adapters.
Echo request and reply
It is used for diagnosis.This pair of messages are used by the network managers and users to identify the network problems
Time stamp request and reply
It is used to determine RTT needed for an IP datagram or synchronize the clocks in 2 machines
Address mask request and reply
It is used to know network address,subnet address and host ID
Router solicitation and advertisement messages
It is used to know the address of routers connected and to know if they are alive and functioning
Redirection
It is used to update the routing table of the host
IP was designed as a protocol with low overhead means what?
It provides only the functions that are necessary to deliver a packet from a source to a destination over an interconnected system of networks. The protocol was not designed to track and manage the flow of packets
A host can send a packet to
Itself,locally,and remotely
Difference between link state vs distance vector in terms of immediate neighbours?
LS - tell all nodes about your immediate neighbours vs in DV, just tell immediate neighbours about least cost distance to all nodes.
Disadvantages of LS over DV
LS has higher messaging overhead (lots of info from telling all nodes), LS has higher processing complexity (has to be done in all routers)
Advantages of LS over DV
LS is less vulnerable to looping - nodes have global info linking
Difference between Link State Routing algorithm and Distance Vector algorithm
LSR = centralised solution, each node tries to find its own best route to the next place vs distance vector is a distributed protocol where nodes collectively try to find best route to destination.
What's inside a router?
Linecards for input, route/control processor, interconnect (switching fabric), linecards for output
LSP
Link State Package
What are the intra-domain routing protocols that each AS runs?
Link State protocol (e.g. Open Shortest Path First), Distance vector protocol (e.g. Routing Info Protocol)
Network Destination
Lists the reachable networks.
Network Destination on routing list
Lists the reachable networks.
Routing Table
MAC table is data link layer Routing Table is network layer. Routing tables use IP addresses
tracert
MS trace route command
Define network service model
The network service model defines the characteristics of end-to-end transport of packets between sending and receiving end systems.
What are some functions of the Network Layer?
Services provided to the transport layer Routing Connection Management (if applicable) Flow Control Error Control Node Identification (Addressing) Segmentation / Reassembly
What metrics might you use in distance vector routing?
Minimise latency, minimise loss rate, minimise price
224-239.0.0.0
Multicast IP range Class D
Generically speaking, what is the point of the network layer?
Naming + addressing
Code 0
Net Unreachable
NAT
Network Address Translation
9
Network Admin Block
6
Network Unknown
Does flooding happen in distance vector routing, and if not what happens instead?
No - instead each router exchanges distance vector info (provisional shortest paths to each other router) with its neighbouring routers
Connectionless
No connection with the destination is established before sending data packets. requires no initial exchange of control information to establish an end-to-end connection before packets are forwarded
Are the fields that fallow the CheckSum field always the same?
No they vary depending on the particular ICMP message that is sent
Router capacity formula
No. of external router ports * speed (line rate) of a port
What happens if the router malfunctions in DV?
Node can advertise incorrect path cost, each nodes''s table is used by others and the error propagates through the network :( the lie spreads...
What happens if the router malfunctions in LS?
Nodes can advertise incorrect link cost, each node computes only its own table
legacy network layer protocols
Novell Internetwork Packet Exchange (IPX) AppleTalk Connectionless Network Service (CLNS/DECNet)
Size of distance vector
Number of routers in the network
Message complexity in DV
O(#iterations * E)
Processing complexity in DV
O(#iterations * N)
How many messages are needed to flood link state messages
O(N * E) where N = no. nodes, E = no. edges in graph
How many entries are there in the forwarding table
O(N)
Message complexity in LS
O(N*E) messages
Processing complexity in LS
O(N^2)
10.0.0.0
Private Class A
172.16-31.0.0
Private Class B
192.168.0-255.0
Private Class C
Private or public 192.168.1.8/24
Private IP Address
Multicast
One to a group IP communications
Broadcast
One to many IP communications
What information is contained in a ICMP error report
Only information about processing of NON-ICMP IP datagrams
Media Independent
Operation is independent of the medium carrying the data.
Best Effort (unreliable)
Packet delivery is not guaranteed. IP does not have the capability to manage and recover from undelivered or corrupt packets. There is no synchronization data included in the packet header for tracking the order of packet delivery. There are also no acknowledgments of packet delivery with IP, and there is no error control data to track whether packets were delivered without corruption.
What is the basic transport unit (PDU) of the Network Layer?
Packets / Datagrams
12
Parameter Problem
What are the inter-domain protocols that establish routes between domains (i.e. AS's)?
Path vector e.g. Borer Gateway Protocol (BGP)
Destination unreachable fragmentation needed and don't fragment was set
Pmtu the router discards the packet if it is too large.
What is the problem with using metrics in distance vector routing?
Problem is if nodes use different criteria e.g. routing algorithm where paths are describes by delay, cost, loss.
Linecards for output
Processes packets before they leave
Linecards for input
Processes packets on their way in
How can you see ICMP messages?
Protocol Analyzers
Dynamic Host Configuration Protocol (DHCP)
Protocol that allows a host to obtain IP address automatically. Can be configured so host receives same or different IP address upon every connection
Internet Control Message Protocol (ICMP)
Protocol used by hosts and routers to communicate messages (typically error messages) to each other.
Route/control processor
Pushes forwarding tables to the linecards, making decisions over long time horizons (network change)
How might you combine more than one metric that you are trying to maximise/minimise?
Put weights next to each of metrics
Routing algorithm classification
Q: global or decentralized information? global: # all routers have complete topology, link cost info # "link state" algorithms decentralized: # router knows physicallyconnected neighbors, link costs to neighbors # iterative process of computation, exchange of info with neighbors # "distance vector" algorithms Q: static or dynamic? static: # routes change slowly over time dynamic: # routes change more quickly * periodic update * in response to link cost changes
a term used to characterize the performance of a network as seen by the users of the network
Quality of service (QoS)
5
Redirect
Autonomous System (AS)
Region of a network under a single administrative entity
Describe: Redirect
Reports alternate more optimal routes
Describe: Destination Unreachable
Reports on reasons why a network not is inaccessible. Important for troubleshooting
Interior routers in an AS
Responsible for constructing and updating the forwarding tables at routers
What constitutes the control plane in a router?
Route/control processor - part of network that deals with paths between hosts. Routing protocols are also part of the control plane, establishing paths between nodes.
10
Router solicitation
How do routers determine whether the arriving datagram is whole or a fragment?
Routers check the identifier, flags, and fragmentation offset of the datagram. The identification number identifies whether the datagrams is whole or fragmented. The offset specifies where the fragment fits in the original IP datagram. The flag bit is 1 if fragmented and flag bit is 0 if it is the last fragment.
Local network route
The network which the host is connected to is automatically populated in the host routing table.
What does adding weighted hop counts do?
Slows routes given a higher hop count
In an IP router, does the software or hardware implement the control plane, doing processing on changes in the network?
Software
What do routers do?
Routes packets - works in "control plane", computes paths the packets will flow.
Routing
Routing is the process of moving packets across a network from one host to a another
How is the forwarding table constructed in link state routing?
Run Djikstra to give the shortest path to all destinations from a node.
SDN perspective: SDN controller
SDN controller (network OS): # maintain network state information # interacts with network control applications "above" via northbound API # interacts with network switches "below" via southbound API # implemented as distributed system for performance, scalability, fault-tolerance, robustness
Forwarding decisions =
SIMPLE. Have to decide which outgoing port to use in single transmission time.
What are the two issues in link state routing?
Scalability, Transient disruptions
IPsec
Security when transferring packets that encrypt the payload of the datagram that can only be decrypted by the sender. Sublayer underneath IP networking layer.
average response time
Sending several Requests one after another allows for measuring an ____________ (measured in ms)
How can you edit ICMP messages?
Software thats made to edit ICMP
4
Source Quench
Source quench
Source quench message in ICMP is used to add a kind of flow control to the IP. When the router or host discards the datagram due to congestion,it sends a source quench message to the sender of the datagram
Next Hop
The next place the router needs to go to to deliver the packet. Think of hops as the number of routers that it goes to
Network Address Translation (NAT)
Standard that enables local-area network (LAN) to use one set of IP address for internal traffic and another set of IP addresses for external traffic. Two purposes: 1. Acts like a firewall for hiding internal IP addresses 2. Enables use of more internal IP addresses. Companies outside with the same IP address will not conflict the internal IP address Uses the NAT Translation Table for WAN to LAN IP address conversion
Stateless Address Autoconfiguration?
Stateless Address Autoconfiguration (SLAAC): - Hosts can obtain an IPv6 address without DHCP server 1. DHCPv6 Client issues RS (router solicitation) which requests for a RA (router advertisement) 2. Router responds with RA containing prefix, prefix length, other info 3. Client will generate its own global IPv6 address from prefix in RA
Define subnet mask
Subnet masks denote which part of the address denotes the subnet address. E.G. 223.1.1.0 /24 where /24 denotes that the 24 leftmost bits define the subnet address If another host wanted to connect to this subnet, the IP address of the host must have the address of 223.1.1.xxx
Define subnet
Subnets are the interfaces used to connect hosts and routers. Example shown below.
Name three switching techniques of the switching fabric
Switching via memory: Interrupt is triggered to routing processor when packet arrives at input port, packet is copied into processor memory, processor uses destination address from packet header to lookup correct output port on forwarding table, packet is copied from memory to output port Switching via bus: Input port sends packet containing the output port header through a single shared bus. The output port the matches the packet header will keep the packet. This is similar to the roundabout analogy except only 1 car can access the roundabout at time Switching via an interconnection network / crossbar: Just look at the diagram
IP is the network layer service implemented by
TCP/IP protocol suite.
What can you use to stop loops from happening?
TTL
Header Checksum in IPv4
The 16-bit field is used for error checking of the IP header. The checksum of the header is recalculated and compared to the value in the checksum field. If the values do not match, the packet is discarded.
Identifier
The 16-bit long _________ field typically carries an OS-specific value (MS OS - 0x0100 or 256 decimal)
Sequence
The 16-bit long __________Number starts with certain initial value - incremented by a certain value in every Request sent (MS OS - increments by decimal 256)
Type, Code, and Checksum
The 4-byte long constant portion contains three required fields
Improved packet handling
The IPv6 header has been simplified with fewer fields. This improves packet handling by intermediate routers and also provides support for extensions and options for increased scalability/longevity.
Who does the ICMP report reachability information to?
The Originator Only
What does the response time from a ping request show you?
The Round Trip time the request took to get their and back
Describe: Time Exceeded
The Time To Live (TTL) value expired in transit
variable portion
The _________________contains message-specific fields that carry additional information
192.168.10.10
The address of the local host.
What do routers select to send on to other nodes in distance vector routing?
The best option from the set of options it has (i.e. shortest path to each node)
Global routing state
The collection of routing state in each of the routers
Define router forwarding plane
The collective functions of the input ports, output ports, and switching fabric
What is the main difference of the connection setup in the transport layer vs network layer?
The connection setup in the transport layer do not involve routers while network layer connection setup includes each router along the path that are fully aware of all the VCs passing through it.
If the control plan fails, what happens to the data path?
The data path is not affected - will keep going using the last table update
default gateway.
The router connected to the local network segment and forwards packets out to a remote destination because a host device does not maintain routing information but default gateway does
Local default route
The default route represents the route that packets must take to reach all remote network addresses. The default route is created when a default gateway address is present on the host. The default gateway address is the IP address of the network interface of the router that is connected to the local network. The default gateway address can be configured on the host manually or learned dynamically.
how to determine class of IPv4 address
The first octet determines class of the ip address
Fragmentation Reassembly Time Exceeded
The host returns a ____________________message to the sender (Type = 11, Code = 1)
255.255.255.255
The last two addresses represent the limited broadcast IP address values for use through either the loopback interface (127.0.0.1) or the host IP address (192.168.10.10). These addresses can be used to find a DHCP server before the local IP is determined.
maximum transmission unit (MTU)
The maximum size of the packet the media can carry
Routing
The network layer provides services to direct packets to a destination host on another network and chooses the best path.
Redirect data gram for the host
Type 5 code 1 shows a better route to the destination host
Redirect data gram for the type of service and network
Type 5 code 2 points to a better route to the destination network using the desired tos level
Next Header in IPV6
This 8-bit field is equivalent to the IPv4 Protocol field. It indicates the data payload type that the packet is carrying, enabling the network layer to pass the data to the appropriate upper-layer protocol. This field is also used if there are optional extension headers added to the IPv6 packet.
Hop Limit in IPV6
This 8-bit field replaces the IPv4 TTL field. This value is decremented by one by each router that forwards the packet. When the counter reaches 0 the packet is discarded and an ICMPv6 message is forwarded to the sending host, indicating that the packet did not reach its destination.
Describe how datagram networks work
The sender end system stamps the packet with its destination address and pops the packet into the network. Each router that passes the packet determines the output link by looking at their forwarding table. Information may arrive out of order. *Note that datagram networks do not maintain connection state information
an observable forwarding behavior of a network node toward a group of IP packets that have the same DSCP value
The six DSCP are used to define a per-hop behavior (PHB); PHB:
Stateful DHCP
The standard DHCP server consisting of DORA (Discover, Offer, Request, ACK)
Where is the routing table located?
The the memory of the router
0x01
The value _________ in an IP header's Protocol field informs a receiver that an ICMP header follows
192.168.10.0 - 192.168.10.255
These addresses all relate to the host and local network. All packets with destination addresses that fall into this category will exit out of the 192.168.10.10 interface.
224.0.0.0
These are special multicast class D addresses reserved for use through either the loopback interface (127.0.0.1) or the host IP address (192.168.10.10).
ff00::/8
These are special reserved multicast class D addresses equivalent to the IPv4 224.x.x.x addresses.
127.0.0.0- 127.255.255.255
These loopback addresses all relate to the direct connection and provide services to the local host.
Remote routes
These routes come from remote networks connected to other routers. Routes to these networks can either be manually configured on the local router by the network administrator or dynamically configured by enabling the local router to exchange routing information with other routers using dynamic routing protocols
Communication administratively prohibited messages
These three messages may help revealing the traffic filtering policy used - often disabled administratively
Destination Address in IPV6
This 128-bit field identifies the IPv6 address of the receiving host.
Source Address in IPV6
This 128-bit field identifies the IPv6 address of the sending host.
Fragment Offset in IPv4
This 13-bit field identifies the order in which to place the packet fragment in the reconstruction of the original unfragmented packet.
Payload Length in IPV6
This 16-bit field is equivalent to the Total Length field in the IPv4 header. It defines the entire packet (fragment) size, including header and optional extensions.
Identification in IPv4
This 16-bit field uniquely identifies the fragment of an original IP packet.
Flow Label in IPV6
This 20-bit field provides a special service for real-time applications. It can be used to inform routers and switches to maintain the same path for the packet flow so that packets are not reordered.
Flags in IPv4
This 3-bit field identifies how the packet is fragmented. It is used with the Fragment Offset and Identification fields to help reconstruct the fragment into the original packet.
Protocol in IPv4
This 8-bit binary value indicates the data payload type that the packet is carrying, which enables the network layer to pass the data to the appropriate upper-layer protocol. Common values include ICMP (1), TCP (6), and UDP (17).
Traffic Class in IPV6
This 8-bit field is equivalent to the IPv4 Differentiated Services (DS) field. It also contains a 6-bit Differentiated Services Code Point (DSCP) value used to classify packets and a 2-bit Explicit Congestion Notification (ECN) used for traffic congestion control.
Version in IPV6
This field contains a 4-bit binary value identifying the IP packet version. For IPv6 packets, this field is always set to 0110.
Direct connection
This is a route to the loopback interface (127.0.0.1)
::1/128
This is equivalent to the IPv4 loopback address and provides services to the local host.
::/0
This is the IPv6 equivalent of the local default route.
2001:0:9d38:953c:2c30:3071:e718:a926/128
This is the global unicast IPv6 address of the local computer.
2001::/32
This is the global unicast network prefix.
fe80::2c30:3071:e718:a926/128
This is the link local IPv6 address of the local computer.
fe80::/64
This is the local link network route address and represents all computers on the local link IPv6 network.
11
Time Exceeded
TTL
Time To Live
13
Timestamp
14
Timestamp Reply
What are Interior Gateway protocols used for?
To exchange routing information within an Autonomous System
What is the role of the network layer?
To move packets from a sending host to a receiving host using its two primary functions: forwarding and routing.
0 1 2; precedence 3 4thbit; D: Delay bit; when set it means to minimize delay 4 5thbits; T: Throughput bit; when set it means to maximize throughput 5 6thbits; R: Reliability bit; when set it means to maximize reliability 7,8 bits are reserved
ToS field
What is ICMP most commonly used for?
Troubleshooting, Connectivity Tests, Path Discovery
RIP communications are UDP based (T or F)
True
an 8-bit field in which the 3 most significant bits are called the IP precedence bits
Type of Service (ToS) field in the original IP header specifications => Differentiated Services (DiffServ)
0x08
Type values __________ identify ICMP Request
0x00
Type values ___________ identify ICMP Reply
Describe: Router Discovery
Used to discover information about routers on the local network segment
What are Exterior Gateway Protocols ?
Used to exchange routing inforamtion between autonomous systems.
Describe: Echo Request/Reply
Used to test reachability. Ping and Trace route are utilities that use this
UDP
User Datagram Protocol
How does a TraceRoute work?
Using the ICMP Echo request While manipulating the TTL value in the IP header
Traceroute
Utility to trace each router hop
Name the three phases in a virtual circuit
VC Setup: Transport layer contacts network layer, network layer determines path between sender and receiver, network layer determines VC number for each link in that path, forwarding table is updated. Data Transfer: Start transferring packets when the connection is established VC Teardown: The VC connection is released and the forwarding table is updated
Significant fields in the IPv4 header include
Version Differentiated Services (DS) Time-to-Live (TTL) - Contains an 8-bit binary value that is used to limit the lifetime of a packet. It is specified in seconds but is commonly referred to as hop count. The packet sender sets the initial time-to-live (TTL) value and is decreased by one each time the packet is processed by a router, or hop. If the TTL field decrements to zero, the router discards the packet and sends an Internet Control Message Protocol (ICMP) Time Exceeded message to the source IP address. The traceroute command uses this field to identify the routers used between the source and destination. Protocol - This 8-bit binary value indicates the data payload type that the packet is carrying, which enables the network layer to pass the data to the appropriate upper-layer protocol. Common values include ICMP (1), TCP (6), and UDP (17). Source IP Address - Contains a 32-bit binary value that represents the source IP address of the packet. Destination IP Address - Contains a 32-bit binary value that represents the destination IP address of the packet.
Describe the IPv4 datagram
Version #: (4-bits) whether it's IPv4 or IPv6 Header length: 4-bits that determine where in the IP datagram the data actually begins Type of service: Bits used to describe which type of datagram is to be used (low delay, high throughput, reliability, etc) Datagram length: Deterimes the total length of IP datagram measured in bytes. Field is 16-bits long Identifier, Flags, Frag Offset: Used for IP fragmentation Time-to-live: How long the datagram can circulate before it is dropped Protocol: Field used to dictate which transport layer protocol will be used (e.g. 6 for TCP and 17 for UDP) Header Checksum: Detects bit errors of the datagram. If the checksum does not match with the computed checksum, error is detected. Source / Destination IP addresses: As it says Options: As it says Data (Payload): As it says *IP datagram carries 20 bytes of header. If TCP segment, datagram carries 40 bytes of header.
Time exceeded
When a datagram reaches the router,the time to live field gets decremented by 1,when the value reaches 0,a time exceeded message must be sent by the router to the original source
Destination unreachable
When a host cannot deliver or the router cannot route the datagram sends a destination unreachable message back to the source host who initiated the datagram
In connectionless the reciever doesn't know?
When it is coming
How does a routing loop occur?
When one router believes the best path to a network is via a second router, and at the same time, the second router believes the best path to that network is through the first router
Function of DHCP servers
Whenever a hosts connects or disconnects, the DHCP servers will allocate or deallocate an IP address
Software defined networking (SDN)
Why a logically centralized control plane? # easier network management: avoid router misconfigurations, greater flexibility of traffic flows # table-based forwarding (recall OpenFlow API) allows "programming" routers * centralized "programming" easier: compute tables centrally and distribute * distributed "programming: more difficult: compute tables as result of distributed algorithm (protocol) implemented in each and every router # open (non-proprietary) implementation of control plane
Where are ICMP messages located?
Within the IP datagram payload
Pmtu of 576
X.25 mtu size - minimum size that must be supported by any tcp/ip host
Do we construct a forwarding table at each node in Link state routing?
Yes
Can packet loss occur in the routing process?
Yes, if there is no memory available for input queues and output queues, packet loss will occur.
Net Unreachable
_________ (Type = 3, Code = 0) - sent by a router that knows the destination network but believes the route to it is down this time (or too far to reach)
Time to Live Exceeded
_________ in Transit message to the sender (Type = 11, Code = 0)
Host Unreachable
___________(Type = 3, Code = 1) - sent by a router that doesn't know the destination network or is unable to locate the destination host
Port Unreachable
___________(Type = 3, Code = 3) - sent by a host that isn't running the UDP service requested by the client
Checksum
a 16-bit value for integrity verification for the ICMP header only (similar to IPv4, deprecated)
What is a Border Gateway Protocol?
a Distance vector protocol and is the replacement for EGP
What is RIP?
a basic distance vector routing protocol
Routing Table
a data file in RAM that is used to store route information about directly connected network, as well as entries of remote networks the device has learned about
Who must manage issues in IP
a higher level protocol aka TCP aka a Connection-oriented protocols, require that control data be exchanged to establish the connection.
Interfaces in IPv6 commonly have two IPv6 addresses
a link local address and a global unicast address
What does the TraceRoute utility identify?
a path from the sender to the target host
The network layer encapsulates what
a segment with an IP header=packet or Transport Layer PDU+IP header=packet.
the definition of Internet Protocol for this layer (layer3-network layer)
a simple connectionless datagram protocol that provides no error recovery and no delivery guarantee
The process of mapping the IP Address to the MAC Address for actual delivery of frames : address resolution is done through dynamic binding, which is required because the NIC may be changed
address resolution
Public IP address
addresses that are displayed directly to the internet.
two things what the network layer is concerned
addressing and routing
routing algorithms
algorithms that calculate the paths taken by packets as they flow from a sender to a receiver. May be centralized (e.g., with an algorithm executing on a central site and downloading routing information to each of the routers) or decentralized (i.e., with a piece of the distributed routing algorithm running in each router)
Code
an 8-bit value that identifies a message subtype within specific type given by the Type value
Type
an 8-bit value that identifies a type of the ICMP message (specific values are managed by IANA)
fragmenting the packet or fragmentation.
an intermediate device, usually a router, must split up a packet when forwarding it from one medium to a medium with a smaller MTU.
Internetworking: key feature
hides network differences with a common protocol
Gateway address
ip address of the host that enables access to the internet or to other networks. Gateway address should always be on the same network as the computer connecting to it.
DNS server address
ip address of the host that takes care of domain name translation to IP
routers
base their forwarding decision on the value in the network-layer (layer 3) field
trace
cisco route command
show ip route command on router
command can be used to display the routing table of a router.
Internetworking
connecting different networks
Input port functions
decentralized switching: # using header field values, lookup output port using forwarding table in input port memory ("match plus action") # goal: complete input port processing at 'line speed' # queuing: if datagrams arrive faster than forwarding rate into switch fabric # destination-based forwarding: forward based only on destination IP address (traditional) # generalized forwarding: forward based on any set of header field values
Directly Connected Routes
directly connected, physical plug in
Addressing end devices
end devices must be configured with a unique IP address for identification on the network. An end device with a configured IP address is referred to as a host.
default route
equivalent for default gateway, it has to be the same and match
ICMP: primary purpose
error report and testing
Switching via memory
first generation routers: # traditional computers with switching under direct control of CPU # packet copied to system's memory # speed limited by memory bandwidth (2 bus crossings per datagram)
1st part: Network Address 2nd part: Host Address
format of IP address
IPv4 history
has been in use since 1983 when it was deployed on the Advanced Research Projects Agency Network (ARPANET),
MTU: desirable packet size
larger b/c more efficient
DHCP: purpose
lease IP addresses to nodes
transport layer
manages the data transport between the processes running on each host
Every network specifies the maximum length of packets that pass through it
maximum transfer unit (MTU)
Metric
mesurement, how routeres measure their conection
192.168.10.0
network address
SDN perspective: control applications
network-control apps: # "brains" of control: implement control functions using lower-level services, API provided by SND controller # unbundled: can be provided by 3rd party: distinct from routing vendor, or SDN controller
ARP: purpose
node uses it to map a local IP address to its Link Layer addresses
Private IP address
one that is not displayed directly to the internet and is normally behind a firewall
Making routing scalable
our routing study thus far - idealized # all routers identical # network "flat" ... not true in practice scale: with billions of destinations: # can't store all destinations in routing tables! # routing table exchange would swamp links! administrative autonomy # internet = network of networks # each network admin may want to control routing in its own network
Loopback
ping yourself, testing yourself
IPv6 datagram format
priority: identify priority among datagrams in flow flow Label: identify datagrams in same "flow." (concept of"flow" not well defined). next header: identify upper layer protocol for data
pp38-
private internets
Routing
process of deciding in which direction to send traffic
Forwarding
process of sending a packet on its way
extension headers (EH)
provide optional network layer information. used for fragmentation, security, to support mobility, and more.
Network Address Translation (NAT)
provides a way for multiple devices to share a single public IP address.
The network layer, or OSI Layer 3
provides services to allow end devices to exchange data across the network. to transport packets between hosts while placing as little burden on the network as possible. The network layer is not concerned with, or even aware of, the type of communication contained inside of a packet
Subnets
recipe # to determine the subnets, detach each interface from its host or router, creating islands of isolated networks # each isolated network is called a subnet
Total Length in IPv4
referred to as the Packet Length, this 16-bit field defines the entire packet (fragment) size, including header and data, in bytes. The minimum length packet is 20 bytes (20-byte header + 0 bytes data) and the maximum is 65,535 bytes.
Command that shows routing table
route print or netstat -r
9
router Advertisements
remote Routes
routes that are not directly connected, at least one other router
router
select paths for and direct packets toward the destination host in a process known as routing. Only concerned with layer 3 network layer and doesn't touch the segment.
:method used to convey number of bits for a given network :describes how the host address bits have been partitioned: how many bits are used for the subnet and how many bits are used for the actual host address
subnet mask
-It uses the same dotted-decimal notation as the IP address -Each bit in the IP address has a corresponding mask bit -If a bit in the IP address is part of the network address, including the subnet, its mask bit is set to 1; otherwise it is set to 0 -Thus, only the bits used for the actual host address have their mask bits set to 0; all other bits have their mask bits set to 1
subnet mask operates in the following manner
:a networking technique used to simplify network administration : worked by borrowing bits from the host address to create two or more subnetworks (or subnets), leaving the network address space untouched since network addresses are unique :permits us to divide the original host address space into two subspaces: a subnet address space and a new host address space
subnetting
-version; 4bits -IHL (IP Header Length); 4bits -DSCP (Differentiated Services Code Point); 6 bits -ECN (Explicit Congesting Notification); 2bits -Total length; 16 bits -Identification; 16 bits -Flags; 3bits -Fragment Offset; 13 bits -Time to Live; 8bits -Protocol; 8bits - Header Checksum; 16bits -Source address; 32 bits -Destination address; 32 bits -Option; variable -Padding; variable
the format of IPv4 header
node.
the host or computer portion of the address
one major characteristic of the media that the network layer considers
the maximum size of the PDU that each medium can transport. This characteristic is referred to as the maximum transmission unit (MTU). The network layer then determines how large packets should be.
Encapsulation
the network layer adds IP header information, such as the IP address of the source (sending) and destination (receiving) hosts. After header information is added to the PDU, the PDU is called a packet.
routing
the network layer must determine the route or path taken by packets as they flow from a sender to a receiver. They do this through routing algorithms. For example, a routing algorithm would determine the path along which packets flow from H1 to H2.
net.
the network portion of the ip address
If reliability overhead were included in IP
then communications that do not require connections or reliability would be burdened with the bandwidth consumption and delay produced by this overhead.
ICMP: stack
top of IP stack
link-layer switch
type of packet switches that base their forwarding decision on values in the fields of the link-layer (layer 2) frame
Source Tree
union of all shortest paths from a source
Sink Tree
union of all shortest paths towards a destiation
IPv4: Networking layer
uses datagrams
command traceroute field
uses this field to identify the routers used between the source and destination.
forwarding
when a packet arrives at a router's input link, the router must move the packet to the appropriate output link. For example, a packet arriving from Host H1 to Router R1 must be forwarded to the next router on a path to Host H2.
Longest prefix matching
when looking for forwarding table entry for given destination address, use longest address prefix that matches destination address.
Command: route print
windows only
Core router
within single AS, join routers together