Cisco Routing

Routing Protocols
Distance Vector Routing	Routing protocols that send their routing tables to their neighbors; uses the distance to a remote network to find the best path (RIP and IGRP) Counting to Infinity -Distance vector routing error that can be remedied by Maximum Hop Count, Split Horizons, Route Poisoning, and Hold-Down timers.
Link State Routing	Sends the state of its own interfaces to every router in the network; determines the entire network topology, then uses SPF (Shortest Path First) algorithm to find best route. (OSPF,EIGRP(hybrid DV+LS)) Link State routing problems -Router resource usage, bandwidth consumption, and update synchronization. Solutions -Lengthening the update frequency, exchanging route summaries, using time stamps, or using sequence numbers can remedy the problems.

Routing Problems:
Convergence	Time it takes all routers to receive an update and agree on optimal routes through the internetwork.
Routing Loops	When two or more routers have not yet converged and are broadcasting inaccurate routes.

Routing Problems&rsquor; Solutions:
Hold-downs	Prevent regular update messages from reinstating a route that is down.
Route Poisoning	If a router's connected network goes down, it sets its hop count to the maximum amount to make the network unreachable.
Split Horizons	Specify that a router can't send information about a route out the interface they originated from.
Maximum Hop Count	DV (RIP) permits hot count of up to 15. So a packet that is caught in a routing loop will only travel 15 hops, on the 16the network is deemed unreachable and the packet is discarded.

Configuring Routing Protocols
Configuring Static Routes Syntax: ip route [dest] [mask] [next_hop \| exit_int] Example: R_3(config)#ip route 192.168.1.0 255.255.255.0 serial0
Configuring RIP (Routing Information Protocol): Syntax: Router(config)#router rip Router(config-router)#network <network #> Example: Router(config)#router rip Router(config-router)#network 10.0.0.0 Router(config-router)#network 192.168.1.0
Configuring IGRP (Interior Gateway Routing Protocol) Syntax: Router(config)#router igrp <autonomous system #> Router(config-router)#network <network #> Example: Router(config)#router igrp 200 Router(config-router)#network 10.128.22.0 Router(config-router)#network 192.168.1.0

Routing Protocols&rsquor; Administrative Distances

Route Source	Default Distance
Connected interface	0
Static Route	1
EIGRP	90
IGRP	100
OSPF	110
RIP	120
External EIGRP	170
Unknown	255

Name Resolution (DNS)

Creating a Host Table

Syntax:

ip host name <tcp port #> <ip address>

The example turns off domain lookups and doesn&rsquor;t specify a port number because port 23 ( telnet ) is used by default.

Example:

Router_2#configure terminal

Router_2(config)#no ip domain-lookup

Router_2(config)#ip host router_3 192.168.1.6

Using DNS lookups

Router_2(config)#ip domain-lookup

Router_2(config)#ip name server 192.168.1.5

Router_2(config)#ip domain-name foo.bar

Subnet Masking

Process

1.) How many subnets?

2(masked bits)-2 = Subnets

2.) How many valid hosts per subnet?

2(unmasked bits)-2=Hosts

3.) What are the valid subnets?

256-(subnet base)=Base number

4.) What are the valid hosts in the subnets?

All numbers between subnets minus the all 1s (.255) and all 0s (.0) host addresses.

5.) What is broadcast address of the subnet?

All the host bits turned on.

Example

255.255.255.192 = 11111111.1111111.1111111.11000000

1.) (22)-2= 2 Subnets

2.)(26)-2= 62 Hosts per subnet

3.) 256 -192= 64 (.01000000) {For the first subnet}

4.) 65 to 126 (.01000001 to .01111110) Valid hosts in the subnets

5.) 127 (.01111111) Broadcast