Exam 2
This routing algorithm is the de-facto standard BETWEEN DIFFERENT Autonomous Systems (AS)
Border Gateway Protocol (BGP)
What is FF:FF:FF:FF:FF:FF, and when would it be used?
Broadcast MAC ARP, D in DHCP
For a network of 172.16.0.0/12, what is: 172.31.255.255
Broadcast address
Describe how a switch knows which MAC addresses are attached to which ports
Builds a switching table automatically... but describe how it works
The following devices process "network layer" information: A. Hubs B. Switches C. Routers D. Hosts
C. Routers and D. Hosts
Slash notation for networks, for example /24
CIDR
______ allows for devices on the network to resolve their own collisions
DHCP
Network Layer
Data Plane, Control Plane, IP addressing, CIDR Notation, Subnetting
Data Plane vs. Control Plane
Data Plane: - Local (per router) - Forwarding Control Plane: - Network-Wide - Routing
OSPF uses a link-state algorithm called ________ algorithm RIP uses a distance vector algorithm called ________ algorithm
Dijkstra's algorithm and Bellman-Ford
This type of routing algorithm exchanges messages between nearby routers, but only for routes to the "next hop"
Distance Vector (Bellman-Ford algorithm)
eBGP
External BGP connection that spans to ASs
ARP matches and links MAC address to IP address (T/F)
FALSE
10.210.55.122 is routable on the internet (T/F)
False
A host can only get its IP address from a network admin (T/F)
False, DHCP
A switch builds and maintains a ______
Forwarding and routing (algorithm/protocols)
What are the key functions of a router?
Forwarding and routing (algorithms/protocols)
Explain the difference between a hub, a switch and a router in terms of the OSI or TCP/IP Data Model
Hub - Layer 1 - repeats electric signal Switch - Layer 2 - only sends data to the MAC addresses as required Router - Layer 3 - determines the route to the destination and sends the data there.
Software Defined Networking (SDN)
Implemented in remote servers, installs forwarding tables in routers
Traditional Routing Algorithms
Implemented in routers
iBGP
Internal BGP session between routers within same ASs
Decentralized
Iterative process of computation, exchange of info with neighbors - Routers initially only know link costs to attached neighbors - distance vector algorithm
In ______ algorithms, all routers have complete topology. In ______ algorithms, router only knows physically connected neighbors.
Link State And Distance Vector
This type of routing algorithm requires all of the routers to build a complete map of the network
Link State Algorithm (Dijkstra's algorithm)
Other not internet- routable addresses
Loopback address (localhost) -127.0.0.1 Link local addresses -169.254.0.0/16 - confusing concept but means that the device could not obtain an IP address
The MAC Address is assigned by
Manufacturer
For a network of 192.168.1.0/24, what is: 192.168.1.0
Network address
Private IP addresses
Not routable on the internet
In the design a simplified network that has several internal routers, and more than one external connection to the Internet... Describe which routing algorithms run on each router.
OSPF on the internal routers OSPF and BGP on the External Routers
This is an example of an interior gateway routing algorithm
Open Shortest Path First (OSPF)
BGP Session
Routers exchange BGP messages over semi-permanent TCP connection, advertise paths to different destination network prefixes
dynamic layer
Routes change more quickly - periodic updates or in response to link cost changes
The ______ algorithm is the determination of the end-to-end path that data should take. This process results in the creation of a ______ table.
Routing Algorithm Creates the Forwarding Table
Control Plane Function
Routing Algorithms, Network Configuration and Management
Scalable routing: Intra-AS/Intra-domain
Routing within same domain - all routers in the AS must run the same protocol - Gateway router at edge of AS had links to gateways in other AS's -determines entries for devices within AS
Data Plane Functions
Routing, Addressing, Forwarding
______ is the process of moving packets from a router's input to the appropriate output. It uses the ______ table.
The forwarding process uses the forwarding table
Link Layer
The shared channel problem; Ethernet, LAN/VLANs, Broadcast Channels
A link-state algorithm requires an entire map of the network before routing tables can be shared (T/F)
True
In a MAC address, what do the first 3 bytes represent?
Who the manufacturer is
SDN: Data Plane Switches
forwarding table computed and installed under controller supervision
Public IP addresses
routable on the internet
Scalable routing: Inter-AS/inter-domain
routing between domains - gateways perform this (in addition too intra-AS) - determines entries for external devices
Describe how the ARP protocol works
•Node does not know the MAC address for an associated IP address •Node sends ARP request to the broadcast Ethernet address •All devices receive this request •The IP owner replies back with an ARP reply
Name the non-routable private IPv4 CIDR ranges, including link-local. There are 5 total networks
- 10.0.0.0/8 - 172.16.0.0/12 - 192.168.0.0/16 - 127.0.0.0/8 - 169.254.0.0/16
IPv6
- 128 bit address written in hexadecimal form - 2001:0df8:00f2::06ee:0000:0f11 - MAC addresses (link layer) look similar but are not related - Created because the world was running out of IPv4 addresses
IPv4
- 32 bit written in dotted decimal notation - 192.168.1.1
LAN; MAC/Ethernet/Physical address
- 48 bit address used to locally get a frame from one interface to another physically-connected interface - burned in NIC-ROM, sometimes software-settable
NAT (Network Address Translation)
- All devices in local network have addresses in a private IP address space that can only be routed in a local network - just one IP address needed from provided ISP for all devices - All datagrams leaving local network will have same source NAT IP address but different source port numbers
Which routing protocol advertises routes between autonomous systems and its subnets
- BGP
Network Layer Service Model: the internet
- Best effort Service - No guarantees of successful delivery of datagrams, timing or order of delivery, or bandwidth available for end to end flow - Simple to use - Bandwidth is sufficient - App-layer service allows connection from various locations -congestion control of elastic services
Switches vs. Routers
- Both are store-and-forward -- routers: network layer devices (examine network-layer headers) -- switches: link-layer devices (examine link-layer headers) - both have forwarding tables -- routers: compute tables using routing algorithms, IP addresses -- switches: learn forwarding table using flooding, learning, MAC addresses
IP addressing and Subnets: INTERFACE
- Connection between host/router and physical link - IP address associated with each host or router interface - Routers typically have multiple interfaces, a host only has one or 2
Multiple access protocols
- Distributed algorithms that determine how nodes share a channel -- communication done on channel - cable access network -> FDM, TDM, and random access
Function of routers in the network layer
- Examine header fields in IP datagrams passing through, move datagrams from input ports to output ports to get them to their final destination
Bellman-Ford Algorithm
- From time-to-time, each node sends its own distance vector estimate to neighbors so they can update their own distance vector - iterative, asynchonous - distributed, self-stopping each node notifies its neighbors only only when its DV has changed
4 layers of the control plane
- Global, Dynamic, Decentralized, Static
With _____, only one side can transmit. With _____ both sides can transmit at the same time
- Half-duplex - Full-duplex
Multiprotocol Label Switching (MPLS)
- High-speed IP forwarding using fixed length labels (rather than shortest prefix matching/destination IP address) -- faster lookup -- Still works alongside IP -Allows for more flexibility better lookup and reroute times
DHCP: 1 of 2 ways to get IP address
- Host dynamically obtains IP address from network server when it joins the network - can renew its lease on address in use - only holds address while connected/on so they can be reused - Process: Discover, Offer, Request, Acknowledge (DORA)
Routing among hosts, in the same AS is ______ routing. Routing among AS'es is _____ routing
- Intra-AS - Inter-AS
Software defined (SDN)
- Logically centralized control, remote controller computes, installs forwarding tables in routers
LANs
- MAC/Ethernet/Physical address - Ethernet - Switches
SDN controller (data plane)
- Maintains network wide state info through distributed database - interacts with network control apps (control plane) and network switches (data plane)
Network Management
- Old, slow way: configure each device individually via the CLI - New, fast way to use SNMP to execute common operations (assigning an address to a router interface) for centralized and management - Communication occur in many ways, server to client request/response, client to server trap (one-way) - MIB contains information used to configure a specific model/vendor specific commands
Open Flow Protocol
- Operates between switch and controller - uses TCP - 3 types of messages: --- Controller-to-switch --- Switch-to-controller/asynchronous --- symmetric (misc)
Forwarding (going through)
- Packet arrives at a single router in the network, router examines a portion of the packets destination address and forwards the packet to an adjacent router - uses forwarding table to map destination addresses and find outbound link for a packet
Intra-AS routing - OSPF
- Publicly available - Classic link-state protocol must be aware of cost of each link in network -- each router constructs a complete topological map of the entire system - Uses Dijkstra's algorithm to computer forwarding table -- installs lowest cost routes into forwarding table (data plane)
The link layer
- Responsible for transferring datagrams between two adjacent devices over a link -flow control, error detection, error correction
Link State
- Rotes determined with knowledge of all routers in the network - each router floods link state advertisements (its routing table) to all routers in the network - uses Dijkstra's algorithm
Distance Vector
- Routes determined by information from direct neighbors - each router sends distance and vector information to its neighbors - uses bellman ford algorithm - distance- link cost - vector- interface
LAN; Switches
- Store and forward ethernet frames - Plug-and-play, self learning devices records sender location pairs in table - hosts have dedicated, direct connection
NAT Translation Table
- Stores source IP address/port# and NAT IP address/port # translation pairs - Remote/client servers use NAT IP address/port # to send datagram, NAT router will translate and forward matching IP address/port # within local network
Inter-AS routing : Border Gateway Protocol (BGP)
- The protocol that glues the thousands of ISPs in the internet together - Selects routes based on: --- local preference value attribute/policy decision --- shortest AS-PATH --- Closest Next-Hop router (hot potato routing) --- Additional criteria
Network Layer: Control Plane 2 approaches
- Traditional per-router control - Software defined (SDN)
Network Layer Data Plane
- Transports segments from sender to receiver, then passes them to the link layer - receiver delivers the segments to transport layer - every internet device had network layer protocols
IP addressing and Subnets: CIDR
- a.b.c.d/x where x is the # of its in the subnet part of the address - 192.168.1.0/24, the first 24 bits of the address are the network portion
VLANs
- allow multiple virtual local area networks to be defined over a single physical local area netowrk infrastructure -increased efficiency, security, and privacy - port based: switch ports group so that a single switch operates as multiple switches -- Forwarding between VLANs done through routing -- Trunk Port (802.1q) carries frames between VLANs defined over multiple switches- adds VLAN tag information
IPv4 vs IPv6
- both address types IF hosts and networks on network layer
Dijkstra algorithm
- centralized network topology - all nodes have same info - computers least cost paths from one node (source) to all other nodes - Each router must broadcast its link state information to other n routers - Iterative: after k iterations, know least cost path to k destinations
Multiple Access Protocols 3
- channel partitioning protocol: divide channel into smaller portions, allocate each to a node for exclusive use -- TDMA, FDMA - Random access protocols: Channel undivided, allow collision and recover from them -- ALOHA, slotted ALOHA -- CSMA, CSMA/CD - Taking turns protocols: nodes take turns, those with more to send have longer turns -- polling, token-passing
Public and Private IP Addresses
- defined by RFC 1918 - 10.0.0.0/8 - 172.16.0.0/12 - 192.168.0.0/16
IP addressing and Subnets: SUBNET
- device interfaces that can reach each other without passing through an intervening router
LAN; Ethernet
- dominant wired LAN technology - unreliable, connectionless -unslotted CSMA/CD with binary backoff
Routing (planning)
- end-to-end process determine the shortest path from routers to the destinations using routing algorithms - Uses shortest paths to configure forwarding tables in routers
Traditional per-router control plane approach
- individual routing algorithm components in each router
The internet: Scalable Routing
- routing aggregated into regions known as domains/autonomous systems (AS) - allows connection across the internet while still maintaining admin control within ones own network - Forwarding table is configured by both intra and inter-AS routing algorithms -Most common protocols: -- routing information protocol (RIP) -- Enhanced interior gateway routing protocol (EIGRP) -- Open shortest path first (OSPF)
Internet control message protocol (ICMP)
- used by hosts and routers to communicate network-level info (error reporting, pings) - Messages carried in IP datagrams - Message= type+code+first 8 bytes of datagram causing error - real world use: ping and traceroute
Address Resolution Protocol (ARP)
-ARP table : translates IP/Network- layer address to MAC/link-layer address for nodes on a subnet - each IP node (host or router) on LAN has one - also stores TTL; time after which address mapping will be forgotten - ARP request sent to all nodes on a LAN via a broadcast frame
Link Layer parts
-Node: hosts, switches, routers, access points - Link: communication channel that connects adjacent nodes along a path - Datagram encapsulated-> frame -- MAC addresses in frame header - Implement in network interface card (NIC) attached to host's system buses -- Ethernet, WIFI card/chip
CSMA
-Simple CSMA: listens before transmitting -- if channel sensed idle, entire frame is transmitted; otherwise it is deferred - CSMA/CD: added collision detection, for wired/Ethernet connections -- collided transmissions are aborted to reduce channel wastage -- collision can still occur, but amount of time wasted in event of one is reduced -- better performance than ALOHA - CSMA/CA: collision avoidance, for wireless connections -- uses
Which subnet size has more host addresses: /20 or /22
/22
DHCP process (DORA)
1. (arriving client): broadcast- is there a DHCP server out there 2. (server): Reply with IP address to use 3. (arriving client): confirms IP to use 4. (server): informs its ok (step 1 and 2 can be skipped if client reuses a previous allocated network address)
IPv4 addresses are ___ bits long
32
An IPv4 address contains _____ bits and is generally formatted ______
32 bits, and is formatted as four octets, separated by dots " . ". E.g. 130.203.151.88
A MAC Address has ____ bits (Ethernet/802.11)
48
A _____ is a grouping of IP addresses. Its size is determined by the number of _____ in the subnet mask that is represented in ____ notation. (E.g. /25 has 128 possible addresses)
A subnet size is determined by the number of bits in the subnet mask, and is represented in CIDR notation.
global layer
All routers have complete topology, link cost info - Link state algorithms