EIGRP Auto Summarization

EIGRP Auto Summarization

Router(config-router)#no auto-summary	Turns off the auto-summarization feature. Networks are summarized at the classful boundary by default
Router(config)#int fa 0/0
Router(config-if)ip summary-address eigrp 100 10.10.0.0 255.255.0.0	Enables manual summarization on this specific interface for the given address and mask

Caution:

EIGRP automatically summarizes networks at the classful boundary. A poorly designed network with discontiguous subnets could have problems with connectivity if the summarization feature is left on. You could have two routers advertise the same network172.16.0.0/16when in fact the intention is for the routers to advertise two different networks172.16.10.0/24 and 172.16.20.0/24.

Recommended practice is that you turn off automatic summarization, use the ip summary-address command, and summarize manually what you need to.

Configuring EIGRP

Configuring EIGRP

Router(config)#router eigrp 100	Turns on the EIGRP process
	100 is the autonomous system (AS) number, which can be a number between 1 and 65535
	All routers in the same AS must use the same AS number
Router(config-router)#network 10.0.0.0	Specifies which network to advertise in EIGRP
Router(config-router)#eigrp log-neighbor-changes	Logs any changes to an EIGRP neighbor adjacency

Tip:

The eigrp log-neighbor-changes command, although optional, is recommended to help with troubleshooting.

Router(config-router)#no network 10.0.0.0	Removes the network from the EIGRP process
Router(config)#no eigrp 100	Disables routing process 100
Router(config-if)#bandwidth x	Sets the bandwidth of this interface to x kilobits to allow EIGRP to make a better routing decision

Tip:

The bandwidth command is used for metric calculations only. It does not change interface performance.

Configuration Example: RIP Ver 2 Routing

Configuration Example: RIP-2 Routing

Figure A shows the network topology for the configuration that follows, which shows how to configure RIP-2 using the commands covered in this chapter.

Figure 8-1. Network Topology for RIP-2 Routing Configuration

Boston Router

Boston>en
Boston#config t
Boston(config)#router rip	Enables RIP routing
Boston(config-router)#version 2	Enables RIP-2
Boston(config-router)#network 172.16.0.0	Advertises directly connected networks (classful address only)
Boston(config-router)#no auto-summary	Turns off autosummarization
Boston(config-router)#exit
Boston(config)#exit
Boston#copy run start

Buffalo Router

Buffalo>en
Buffalo#config t
Buffalo(config)#router rip	Enables RIP routing
Buffalo(config-router)#version 2	Enables RIP-2
Buffalo(config-router)#network 172.16.0.0	Advertises directly connected networks (classful address only)
Buffalo(config-router)#no auto-summary	Turns off autosummarization
Buffalo(config-router)#Cntl+z	Exits back to privileged mode
Buffalo#copy run start

Bangor Router

Bangor>en
Bangor#config t
Bangor(config)#router rip	Enables RIP routing
Bangor(config-router)#version 2	Enables RIP-2
Bangor(config-router)#network 172.16.0.0	Advertises directly connected networks (classful address only)
Bangor(config-router)#no auto-summary	Turns off autosummarization
Bangor(config-router)#Cntl+z	Exits back to privileged mode
Bangor#copy run start

RIP Version 2: Optional Commands

RIP Version 2: Optional Commands

Router(config-router)#no version 2	Changes back to RIP-1
Router(config-router)#version 1	Changes RIP routing to RIP-1
Router(config-router)#no auto-summary	RIP-2 summarizes networks at the classful boundary. This command turns autosummarization off
Router(config-router)#auto-summary	Re-enables autosummarization at the classful boundary

RIP Version 2: Mandatory Commands Networking How-to

RIP Version 2: Mandatory Commands


Router(config)#router rip

Turns on the RIP routing process; the same command as used for RIP Version 1 (RIP-1)


Router(config-router)#version 2

Turns on Version 2 of the routing process. Version 1 is default


Router(config-router)#network w.x.y.z

w.x.y.z is the network number of the directly connected classful network you want to advertise

Troubleshooting RIP Networking How-to

Troubleshooting RIP Issues

Router#debug ip rip	Displays all RIP activity in real time
Router#show ip rip database	Displays contents of the RIP database

RIP Version 2 Networking How-to

RIP Version 2

Note:

RIP-2 is not currently part of the CCNA certification exam. Commands are listed here for reference only.

Router(config-router)#version 2	RIP will now send and receive RIP-2 packets globally
Router(config-if)#ip rip send version 1	Interface will send only RIP-1 packets
Router(config-if)#ip rip send version 2	Interface will send only RIP-2 packets
Router(config-if)#ip rip send version 1 2	Interface will send both RIP-1 and RIP-2 packets
Router(config-if)#ip rip receive version 1	Interface will receive only RIP-1 packets
Router(config-if)#ip rip receive version 2	Interface will receive only RIP-2 packets
Router(config-if)#ip rip receive version 1 2	Interface will receive both RIP-1 and RIP-2 packets

RIP Routing: Optional Commands Networking How-to

RIP Routing: Optional Commands Router(config)#no router rip Turns off the RIP routing process Router(config-router)#no network w.x.y.z Removes network w.x.y.z from the RIP routing process Router(config-router)#passive-interface s0/0 RIP updates will not be sent out this interface Router(config-router)#neighbor a.b.c.d Defines a specific neighbor with which to exchange information Router(config-router)#no ip split-horizon Turns off split horizon (on by default) Router(config-router)#ip split-horizon Re-enables split horizon Router(config-router#timers basic 30 90 180 270 360 Changes timers in RIP: 30 = Update timer (in seconds) 90 = Invalid timer (in seconds) 180 = Hold-down timer (in seconds) 270 = Flush timer (in seconds) 360 = Sleep time (in milliseconds) Router(config-router)#maximum-paths x Limits the number of paths for load balancing to x (4 = default, 6 = maximum) Router(config-router)#default-information originate Generates a default route into RIP

RIP Routing: Mandatory Commands Networking How-to

RIP Routing: Mandatory Commands

Router(config)#router rip	Enables RIP as a routing protocol
Router(config-router)#network w.x.y.z	w.x.y.z is the network number of the directly connected network you want to advertise

Note:

You need to advertise only the classful network number, not a subnet:

Router(config-router)#network 172.16.0.0 

not

Router(config-router)#network 172.16.10.0 

If you advertise a subnet, you will not receive an error message, because the router will automatically convert the subnet to the classful network address.

IP Classless Command Networking How-to

IP Classless

Router(config)#ip classless

Instructs IOS to forward packets destined for an unknown subnet to the best supernet route


Router(config)#no ip classless

Turns off the ip classless command


Note:
A supernet route is a route that covers a range of subnets with a single entry.

Note:
The ip classless command is enabled by default in Cisco IOS Software Release 11.3 and later.

Verifying Static Routes Networking How-to

Verifying Static Routes


Router#show ip route --------> Displays contents of IP routing table


Note:

The codes to the left of the routes in the table tell you from where the router learned the routes. A static route is described by the letter S.

Routing: Default Routing Networking How-to

Default Routing

Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.10.2	Send all packets destined for networks not in my routing table to 172.16.10.2
Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0	Send all packets destined for networks not in my routing table out my Serial 0/0 interface

Routing: Static Routing Networking How-to

Static Routing

When using the ip route command, you can identify where packets should be routed to in two ways:

• The next-hop address

• The exit interface

Router(config)#ip route 172.16.20.0 255.255.255.0 172.16.10.2	172.16.20.0 = destination network
	255.255.255.0 = subnet mask
	172.16.10.2 = next-hop address
	Read this to say: To get to the destination network of 172.16.20.0, with a subnet mask of 255.255.255.0, send all packets to 172.16.10.2
Router(config)#ip route 172.16.20.0 255.255.255.0 s0/0	172.16.20.0 = destination network
	255.255.255.0 = subnet mask
	s0/0 = exit interface
	Read this to say: To get to the destination network of 172.16.20.0, with a subnet mask of 255.255.255.0, send all packets out interface Serial 0/0

The permanent Keyword (Optional)

Router(config)#ip route 172.16.20.0 255.255.255.0 172.16.10.2 permanent	Specifies that the route will not be removed, even if the interface shuts down

Without the permanent keyword in a static route statement, a static route will be removed if an interface goes down. If you don't tighten those serial cables or if you have a bad connector on a UTP cable, a cable can easily become loose, causing an interface to go down. But plugging the cable back in does not add that static route back into the routing table. The only way to get that route back into the table is to reload the router or use the permanent keyword in your ip route command. This option is especially useful when the night janitor knocks a cable loose and replaces it, hoping no one will notice. Can your network afford to lose a route for a few hours until the next morning when you or your IT staff comes in to work? The permanent keyword is also useful in helping to avoid constant shortest path first (SPF) calculations in OSPF when there is a flapping link; if the link goes down, the route will stay in the routing table.

However, you must be careful when using this optional keyword. You might want that route to be removed from the routing table. You might also want to know why the night janitor was in your wiring closet in the first place.

Static Routes and Administrative Distance (Optional)

Router(config)#ip route 172.16.20.0 255.255.255.0 172.16.10.2 200	Specifies that an administrative distance of 200 has been assigned to this route.

Note:

By default, a static route is assigned an administrative distance (AD) of 1. Administrative distance rates the "trustworthiness" of a route. AD is a number from 0-255, where 0 is absolutely trusted, and 255 cannot be trusted at all. Therefore, an AD of 1 is an extremely reliable rating, with only an AD of 0 being better. An AD of 0 is assigned to a directly connected route. The following table lists the administrative distance for each type of route.

Route Type	Administrative Distance
Connected	0
Static	1
EIGRP Summary Route	5
EBGP	20
EIGRP (Internal)	90
IGRP	100
OSPF	110
IS-IS	115
RIP	120
EGP	140
On-Demand Routing	160
EIGRP (External)	170
iBGP (External)	200
Unknown	255

Tip:

By default, a static route will always be used instead of a routing protocol. By adding an AD number to your ip route statement, however, you can effectively create a backup route to your routing protocol. If your network is using EIGRP, and you need a backup route, add a static route with an AD greater than 90. EIGRP will be used because its AD is better (lower) than the static route. But if EIGRP goes down, the static route will be used in its place. This is known as a floating static route.

Configuration Example: Basic Router Configuration

Figure A shows the network topology for the configuration that follows, which shows a basic router configuration using the commands covered in this chapter.

Figure A. Network Topology for Basic Router Configuration

Boston Router

Router>en	Enters privileged mode
Router#clock set 18:30:00 15 Nov 2004	Sets local time on router
Router#config t	Enters global config mode
Router(config)#hostname Boston	Sets router name to Boston
Boston(config)#no ip domain-lookup	Turns off name resolution on unrecognized commands (spelling mistakes)
Boston(config)#banner motd #	Creates an MOTD banner
This is the Boston Router.
Authorized Access Only
#
Boston(config)#clock timezone EST 5	Sets time zone to Eastern Standard Time (5 from UTC)
Boston(config)#enable secret cisco	Enables secret password set to cisco
Boston(config)#service password-encryption	Passwords will be given weak encryption
Boston(config)#line con 0	Enters line console mode
Boston(config-line)#logging sync	Commands will not be interrupted by unsolicited messages
Boston(config-line)#password class	Sets password to class
Boston(config-line)#login	Enables password checking at login
Boston(config-line)#line vty 0 4	Moves to virtual Telnet lines 0 through 4
Boston(config-line)#password class	Sets password to class
Boston(config-line)#login	Enables password checking at login
Boston(config-line)#line aux 0	Moves to line auxiliary mode
Boston(config-line)#password class	Sets password to class
Boston(config-line)#login	Enables password checking at login
Boston(config-line)#exit	Moves back to global config mode
Boston(config)#no service password-encryption	Turns off password encryption
Boston(config)#int fa 0/0	Moves to Fast Ethernet 0/0 mode
Boston(config-if)#desc Engineering LAN	Sets locally significant description of the interface
Boston(config-if)#ip address 172.16.10.1 255.255.255.0	Assigns IP address and subnet mask to the interface
Boston(config-if)#no shut	Turns on the interface
Boston(config-if)#int s0/0	Moves directly to Serial 0/0 mode
Boston(config-if)#desc Link to Buffalo Router	Sets locally significant description of the interface
Boston(config-if)#ip address 172.16.20.1 255.255.255.0	Assigns IP address and subnet mask to the interface
Boston(config-if)#clock rate 56000	Sets a clock rate for serial transmission. DCE cable must be plugged into this interface
Boston(config-if)#no shut	Turns on the interface
Boston(config-if)#exit	Moves back to global config mode
Boston(config)#ip host buffalo 172.16.20.2	Sets a local host name resolution to IP address 172.16.20.2
Boston(config)#exit	Moves back to privileged mode
Boston#copy run start	Saves running-config to NVRAM

Erasing Configurations - Networking How-to

Erasing Configurations

Router#erase start	Deletes the startup-config file from NVRAM

Tip:

Running-config is still in dynamic memory. Reload the router to clear the running-config.

Saving Configurations - Networking How-to

Saving Configurations

Router#copy run start	Saves the running-config to local NVRAM
Router#copy run tftp	Saves the running-config remotely to TFTP server

exec-timeout Command - Networking How-to

exec-timeout Command

Router(config)#line con 0
Router(config-line)#exec-timeout 0 0	Sets time limit when console automatically logs off. Set to 0 0 (minutes seconds) means console never logs off
Router(config-line)#

Tip:

exec-timeout 0 0 is great for a lab because the console never logs out. This bad security is very dangerous in the real world.