So far in this extended series we have set up some trunking and etherchannel in part 1, PPP in part 2, OSPF in part 3, and RIPv2 in part 4. In this part we will cover EIGRP, before we can then move on to redistributing our routing protocols into each other.

To remind ourselves of the topology here is the layout:

We will be using the following IP addressing schemes:

R4 – s0/2 – 10.25.1.1/24
R5 – s0/2 – 10.35.1.1/24
R8 – s0/0 – 10.25.1.2/24, s0/1 – 10.30.1.1/24. s0/2 – 10.31.1.1/24
R9 – s0/0 – 10.35.1.2/24, s0/1 – 10.30.1.2/24
R10 – s1/0 – 10.31.1.2/24

The exam guide lists the following as things we need to know for EIGRP:

2.50 Implement IPv4 Enhanced Interior Gateway Routing Protocol (EIGRP) 
   (a) Best path 
   (b) Loop-free paths 
   (c) EIGRP operations when alternate loop-free paths are available, and when they are not
   (d) EIGRP queries 
   (e) Manual summarization and autosummarization 
   (f) EIGRP stubs 

So what can we do with our EIGRP network to fulfil the requirements? We can set up an EIGRP stub on R10, using some loopbacks we can do some summarization, and tune our path selection between R5 and its connections between R4 and R9. So hopefully we can tick most of the boxes. First let’s get a brief overview of EIGRP. C and D would be best left (due to the length of discussion) for reading outside of this post, grab a copy of the Odom book for these.

A (very) brief overview of EIGRP

EIGRP is Cisco proprietary, its a hybrid routing protocol with features from both distance-vector and link-state protocols. EIGRP uses the DUAL (Diffusing Update Algorithm) to determine the best path to use, and to ensure a loop-free network. 

Like BGP, EIGRP will form neighbor relationships with adjacent routers in the same AS (Autonomous System). Traffic uses the IP address 224.0.0.10 via either multicast or unicast. Updates are only sent when a change occurs.

EIGRP supports VLSM, has an administrative distance of 90 for local routes, and 170 for routes that have originated outside of the local AS. Metrics used by EIGRP are bandwidth and delay, but can also factor in reliability, load and MTU.

I am not going to explain everything about EIGRP, as this would make for a very long post, there are a number of very good books on the subject and I would again refer you to the CCIE Routing and Switching guide by Wendell Odom for a complete explanation. Before we jump into the configuration I will briefly explain what the FD is though. The FD is the Feasible Distance, and this is the route with the lowest metric (therefore preferred) to each network, when it is added to the routing table it is known as the Successor. An alternate route is the Feasible Successor (FS)

Basic EIGRP configuration

According to our topology and IP addressing above the routers have been set up as follows:

R4 configuration
We start by assigning the IP address to the interface.

interface Serial0/2
 ip address 10.25.1.1 255.255.255.0

We then create the EIGRP process with an AS of 10.

R4(config)#router eigrp 10
R4(config-router)#no auto-summary
R4(config-router)#network 10.25.1.0 0.255.255.255

interface Serial0/2
 ip address 10.25.1.1 255.255.255.0
!
router eigrp 10
 network 10.0.0.0
 no auto-summary

interface Serial0/0
 ip address 10.20.1.2 255.255.255.0
 serial restart-delay 0
!
interface Serial0/1
 ip address 10.20.2.1 255.255.255.0
 serial restart-delay 0
!
interface Serial0/2
 ip address 10.35.1.1 255.255.255.0
 serial restart-delay 0
!
interface Serial0/3
 no ip address
 shutdown
 serial restart-delay 0
!
!
router eigrp 10
 network 10.0.0.0
 no auto-summary

interface Serial0/0
 ip address 10.25.1.2 255.255.255.0
!
interface Serial0/1
 ip address 10.30.1.1 255.255.255.0
!
interface Serial0/2
 ip address 10.31.1.1 255.255.255.0
!
router eigrp 10
 network 10.0.0.0
 no auto-summary

interface Serial0/0
 ip address 10.35.1.2 255.255.255.0
!
interface Serial0/1
 ip address 10.30.1.2 255.255.255.0
!
router eigrp 10
 network 10.0.0.0
 no auto-summary

interface Serial1/0 
 ip address 10.31.1.2 255.255.255.0
!
router eigrp 10 
 network 10.0.0.0
 no auto-summary

R5#conf t
R5(config)#int s0/2
R5(config-if)#bandwidth 64
R5(config-if)#exit
R5(config)#exit

R9#conf t
R9(config)#int s0/0
R9(config-if)#bandwidth 64
R9(config-if)#exit
R9(config)#

R5#conf t
R5(config)#int s0/0
R5(config-if)#shut
R5(config-if)#exit
R5(config)#exit
R5#

R5(config)#int s0/0
R5(config-if)#no shut
R5(config-if)#exit
*Nov  5 13:53:14.657: %LINK-3-UPDOWN: Interface Serial0/0, changed state to up
*Nov  5 13:53:15.661: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up
R5(config)#exit
R5#
*Nov  5 13:53:17.081: %SYS-5-CONFIG_I: Configured from console by console
*Nov  5 13:53:23.433: %DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 10.20.1.1 (Serial0/0) is up: new adjacency

R10(config)#int lo0
R10(config-if)#ip address 172.20.20.1 255.255.255.0
R10(config-if)#int lo1
R10(config-if)#ip address 172.20.30.1 255.255.255.0
R10(config-if)#exit
R10(config)#router eigrp 10
R10(config-router)#network 172.20.20.0 0.255.255.255
R10(config-router)#network 172.20.30.0 0.255.255.255
R10(config-router)#exit

R10(config)#int lo2
R10(config-if)#ip address 172.20.40.1 255.255.255.0
R10(config-if)#int lo3
R10(config-if)#ip address 172.20.41.1 255.255.255.0
R10(config-if)#exit
R10(config)#int s1/0
R10(config-if)#ip summary-address eigrp 10 172.20.40.0 255.255.254.0
R10(config-if)#exit

R10(config)#router eigrp 10
R10(config-router)#eigrp stub connected
R10(config-router)#
*Nov  5 13:35:44.125: %DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 10.31.1.1 (Serial1/0) is down: peer info changed
*Nov  5 13:35:45.021: %DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 10.31.1.1 (Serial1/0) is up: new adjacency
R10(config-router)#exit

R10(config-router)#eigrp stub connected summary
R10(config-router)#
*Nov  5 13:37:30.293: %DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 10.31.1.1 (Serial1/0) is down: peer info changed
*Nov  5 13:37:31.069: %DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 10.31.1.1 (Serial1/0) is up: new adjacency

R10(config)#router eigrp 10
R10(config-router)#eigrp stub