Network+ Module 3 SUPER STUDIER

rogue DHCP server

DHCP client will acept IP info from the first DHCP it hears, sometimes resulting in adding the wrong one. Someone in teh org brings in a home router and plugsit into the network or someone is attacking your server

Address Resolution Protocol (ARP)

How TCP/IP network figures out the MAC address based on the destination IP address. Sends request packet to all network elements, asks for MAC address from specific IP

network block

IANA passes out IP addresses in contiguous chunks called these (class A - E IP addresses)

subnetting

IP addresses and chopping it up into multiple smaller groups. CIDR and subnetting are virtually the same thing. CIDR is done by an ISP-itis given a block of addresses, subnets the block into multiple subnets, and then passes out the smaller individual subnets to customers.

private IP addresses

IP addresses used in networks that either aren't connected to the internet or include computers they want to hide from the rest of the internet. 10.0.0.0 - 10.255.255.255 CLASS A, 172.16.0.0-172.31.255.255 CLASS B, 192.168.0.0-192.168.255.255 CLASS C

IP addressing

IP packet is completely encapsulated inside Ethernet frame. Frame has both a destination MAC address and a source MAC address, while IP packet encapsulated in Ethernet frame has both a source IP address and a destination IP address

IP exclusion

If IP address configured for static that you don't want DHCP server to issue, IP exclusion is used.

segment

TCP chosp up data into these, gives them a sequence number, and then verifies that all of these were received. If it goes missing, the receiving system must request the missing these.

IP helper

TO make DHCP relay-capable device work, you must give the relay the IP address of the real DHCP server, also known as the IP helper address

convergence

(steady state) meaning the updating of the routing tables for all the routers has completed. Assuming nothing changes in terms of connections, the routing tables will not change. In this example, ti takes three iterations to reach convergence.

ephemeral port numbers

1024-5000

Internet Protocol version 4 (IPv4)

192.168.1.115, four values ranging from 0 to 255, separated by three periods.

routing information protocol (RIP) v1

1980s, predeccessors go back to 60s. Max hop count of 15, so your router will not talk to another touer more than 15 routers away. This plagues RIP because a routing table request can literally loop al the way around back to the initial router.

host ID

202.120.10.x, x is host ID, combined with the network ID creates individual system's IP address

dynamic port numbers or private port numbers

49152-65535

*Classless

Another name for CIDR address, meaning the subnet used down not conform to the big three on the classful side.

MAC reservation

Assigns a specific IP address to a specific MAC address. ANytime system with that MAC address makes a DHCP request the DHCP reservation guarantees that the system will get the same IP address.

path vector

BGP is a path vector routing protocol

link state

OSPF and IS-IS, route changes are announced and forwarded as they appear. More efficient routing protocol.

american registry for internet numbers (ARIN)

Regional internet registry that parcels out IP addresses to large ISPs in NOrth America

DHCP lease

Set for a fixed amount of time, one to eight days. Near end of lease, DHCP client sends another DHCP request message

*DHCP relay

Sometimes orgs require many DHCP servers, relay accepts DHCP broadcasts from clients and then sends them via unicast addresses directly to the DHCP server. TO make relay-capable device work, you must give the relay the IP address of the real DHCP server, also known as the IP helper address.

subnet mask

string of ones followed by some number of zeroes, 32 bits, TPed into every TCP/IP host. Helps computer know if IP address is local or long distance.

destination LAN IP

a defined entwork ID. Every network ID directly connected to one of the router's ports is always listed here.

gateway router

acts as the default gateway for a number of client computers

RIPv2

adopted in 94, current version of RIP. works the same as v1 but VLSM has been added and authentication is built into the protocol.

yost cable

also known as rollover cable. classic cisco console cable.

connection

another name for session, refers to teh connection in general, rather than anything specific to TCP/IP.

router

any piece of hardware or software that forwards packets based on their destination IP address. Routers work at the network layer of the OSI model and at the internet layer of the TCP/IP model

Dynamic Host Configuration Protocol (DHCP)

automatically assigns an IP address whenever a computer connects to the network. Any network using DHCP consists of a DHCP server and lots of DHCP clients. Clients request IP info from DHCP servers. DHCP servers in turn pass out IT information to the clients. Most hosts are DHCP clients (desktops, laptops, and mobile devices). most networks have a single DHCP server that often is built into a router for SOHO networks or runs on a server

exterior gateway protocol (EGP)

autonomous systems communicate with each other using a protocol called exterior gateway protocol (EGP). The network or networks within an AS communicate with protocols as well; these are called generically interior gateway protocols (IGPs)

classless inter-domain routing

based on concept called subnetting: taking single class of IP addresses and chopping it up into multiple smaller groups. Done by ISP - it is given a block of addresses, subnets the block into multiple subnets, then passes out the smaller individual subnets to customers.

interface

tells router which of its ports to use.

routing table

the actual instructions that tell teh router what to do with incoming packets and where to send them

automatic private IP addressing (APIPA)

based on concept called subnetting; take single class of IP addresses and chop it up into multiple smaller groups. Done by the ISP - it is given a block of addresses, subnets the block into multiple subnets, then passes out the smaller individual subnet

connection-oriented

both sides of the communication acknowledge each other before conducting communication

Cisco IOS

cisco's proprietary OS that most their products (routers) run.

enhanced interior gateway routing protocol (EIGRP)

cisco's proprietary protocol. Back in teh days when RIP was dominant, there was outcry for an improved RIP, but OSPF wasn't yet out. Cisco being the dominant router company in the world came out with IGRP, replaced EIGRP.

TCP Three-way handshake

client sends syn segment to web server, server responds with sync, ack. Client then sends single ack and immediately requests that server begin the web page.

transmission control protocol (TCP)

connection-oriented protocol used with TCP/IP is called this. Gets application's data from one machine to another reliably and completely

user datagram protocol (UDP)

connectionless oriented protocol is called this.

bandwidth

connections handle more data than others

classful

describes the traditional class blocks A-E

port forwarding

designate a specific local address for various network services. Computers outside the network can request a service using the public IP address of the router and the port number of the desired service. The port-forwarding router would examine the packet, look at the list of services mapped to local addresses, and then send that packet along to the proper recipient.

*DHCP four-way handshake (DORA)

discover, offer, request and acknowledgement.

dotted decimal notation

dotted octet numbering system: shortway way for people to discuss and configure the binary IP addresses computers use. 11000000 = 192

hop

each time a packet goes through a router.

transmission control protocol (TCP)

enables connection-oriented communication in networks that use the TCP/IP protocol suite. TCP is by far the most common type of session on a typical TCP/IP network.

internet group management protocol (IGMP)

enables routers to communicate with hosts to determine a group membershi. IE multicast is in the Class D range.

trivial file transfer protocol (TFTP)

enables transfer files from one machine to another. Using UDP, doesn't have any data protection, so you would never use TFTP between computers across the Internet. The typical scenario for using TFTP is movign files between comptuers on the same LAN, where the chances of losing packets is very small. POrt 69.

broadcast

every computer on the LAN hears the message

intermediate system to intermediate system (IS-IS)

extremely similar to OSPF. Uses the concept of areas and send-only updates to routing tables. Dev'd at roughly same time as OSPF and works with IPv6 from the start. De facto standard for ISPs. Link state dynamic routing protocol.

hop count

fundamental metric value for the number of routers a packet will go through on the way to its destination network.

next hop

gateway: IP address for the next hop router; in other words where the packet should go. If the outgoing packet is fora network ID that's not directly connected to the router, gateway column tells the router the IP address of a router to which to send thispacket. That router then handles the packet, and your router is done. If network ID is directly connected to the router, then you don't need a gateway. If there is no gateway needed, most routing tables put either 0.0.0.0 or On-link in this column

border gateway protocol (BGP)

glue of internet, connecting all of the autonomous sytems. Current version of BGP is BGP-4. Internet has settled on this protocol for communication between each AS.

delay

hundreds issues occur that slow down network connections between routers. issues collectively are known as latency

socket

in TCP/IP, session ifno (IP address and port number) stored in RAM is called a socket or "endpoint"

ipconfig

in windows use to display IP and mac address (ifconfig for MAC and Linux)

HTTP (hypertext transfer protocol)

is the underlying protocol used by the web, and it runs, by default, on TCP port 80.

registered ports

less common tcp/ip apps can register their ports with the IANA. unlike well known ports, anyone can use these port numbers for their servers or for ephemeral numbers on clients. Most OS steer away from using these port numbers for ephemeral ports. Opting instead for the dynamic/private port numbers.

internet control message protocol (ICMP)

these features are called automatically by applications as needed without direct user action, includes ping utility

subnet mask

to define a network ID, you need a subnet mask

dynamic NAT (DNAT)

many computers can share a pool of routable IP addresses that number fewer than the computers. The NAT might have 10 routable IP addresses, for example, to serve 40 computers to the LAN. LAN traffic uses the internal, private IP addresses. When PC request info beyond network, NAT doles out a routable IP address from its pool for that communication, Also called pooled NAT.

static NAT

maps a single routable (that is, not private) IP address to a single machine, enabling you to access that machine from outside the network. The NAT keeps track of teh IP address or addresses and applies them permanently on a one-to-one basis with computers on the network.

open shortest path first (OSPF)

most common IGP in the world. Most large enterprises use OSP on their internal networks. Even an AS< while still using BGP on its edge routers, will use OSPF internally because OSPF was designed from the ground up to work within a single AS>OSPF converges dramatically faster and is much more efficient than IRP. Odds are good that if you are using dyanmic, you're using OSPF. They send out hello packets, looking for other OSPF routers. After two adjacent routers form a neighborship through hello packets, exchange info about routers and networks through link state advertisement (LSA) packets. LSAs sourced by each router and are flooded from router to router through each OSPF area.

dynamic routing

most routers have the ability to update their routes dynamically with dynamic routing protocols

protocol suite

no single protocol could do everything a network needed to do, so companies lumped together all their necessary protocols under this term.

unicast

one computer sends a message directly to another user

autonomous system (AS)

one or more networks that are governed by a single dynamic routing protocol within that AS. Does not deliver data between each other using IP, but rather use a special globally unique autonomous system number (ASN) assigned by IANA. Originally a 16-bit number, current ASNs are 32 bits, displayed as two 16 bit numbers separated by a dot.

static addressing

one way to give a host an IP address, subnet mask, and default gateway, by typing them in manually

internet assigned numbers authority (IANA)

org formed to track and disperse IP addresses. Oversees five regional internet registries (RIRs) that parcel out IP addresses to large ISPs and major corporations

*network ID

part of IP addres that is hsared among network ie 202.120.10. is network portion fo IP address. Having a host ID of 0 is reserved for network ID's

well-known port numbers

port number is 16-bit value between 0 and 65535. port numbers from 0 to 1023 are well known.

metric

relative value that defines the cost of suing this route. Lowest routes always win. Routers always use route with the metric of 1, unless it stop working.

NAT translation table

router compares the incoming destination port and source IP address to the entry in the NAT translation table to determine which IP address to put back on the packet. It then sends the packet to the correct computer on the network.

default gateway

router interface that connects a single LAN to the router is known as this. Same network ID as the host

managed devices

routers and advanced switches that have some form of configuration interface

static routes

routers have static routes, either detected by the router at setup or manually entered.

network address translation (NAT)

routers running NAT hide the IP addresses of computers on the LAN but still enable those computers to communicate with the broader internet. Not routing, but a separate technology.

distance vector

routing protocols that calculate the total cost to get to particular network ID and compare that cost to the total cost of all the other routes to get to that same network ID. router then chooses the route with the lowest cost.

user datagram protocol

runs a distant second place to TCP in terms of the number of apps that use it. Used for sessions that don't require the overhead of all that connection-orietned stuff

dynamic addressing

server program running on a system that automatically passes out all the IP info to systems as they boot up or connect to a network

protocol

set of rules and software written to follow these rules are broken down into individual rules or languages are called this.

my traceroute (MTR)

similar to traceroute, but dynamic, continually updating the route that you've selected. You wont' find MTR in windows, rather Linux instead.

session

single communication between a computer and another computer. when you open a web page, that's a session. When you call your friend via the internet, that's a session.

open port

socket respond to any IP packets destined for that socket's port number is called an open port or listening port.

cost

some routing protocols use a cost metric for the desirability of that particular route. A route through a low-bandwidth connection, for example, would have a higher cost value than a route through a high-bandwidth connection. A network administrator can also manually add cost to routes to change the route selection.

zero-configuration networking (zeroconf)

special IP address generated when DHCP client tries to get a DHCP address and fails.

connectionless

start sending data and hope they hear it

network management software (NMS)

tools that describe visualize and configure their entire network. Knows how to talk to your routers, switches, and even PCs to give you an overall view of your network. NMS manifests as a web site where admins may inspect the status of the network and make adjustments as needed.

netstat

universal "show me the endpoint" utility. Netstat works at the command line, show two connections, computer IP address, port #.

port address translation

uses port numbers to map traffic from specific machines in teh network,f orm of NAT that hadnles one to many connections.

route redistribution

when a router takes routes it has learned by one method, say RIP or a statically set route, and announces those routes over another protocol such as OSPF, called route and redistribution. Feature can come in handy when you have a mix of equipment and protocols in your network, such as occurs when you switch vendors or merge with another org.

DHCP scope

when a technician installs a range or pool of IP addresses, this is called a DHCP scope. Passes out other info, like default gateway, DNS server, network time server and so on.

loopback address

when you tell a device to ping 127.0.01, you're telling that device to send the packets to itself

multicast

where a single computer sends a packet to a group of interested computers. How routers talk to each other

internet control message protocol (ICMP)

works at layer 3 to deliver connectionless packets. Handles mundane issues such as host unreachable messages. Ping uses ICMP by sending ICMP packet called echo request to an IP address you specify.

internet protocol (IP)

works at the internet layer, taking data chunks from the transport layer, adding addressing, and creating the final IP packet. Then hands the IP packet to the link layer for encapsulation into a frame.

datagram

works best when you have a lot of data that doesn't need to be perfect or when the systems are so close to each other the chances of a problem occuring are too small to bother worrying about.

variable length subnet masking (VLSM)

you can vary the size ofthe subnets created with this. ISPs might do this to accommodate customer needs