The lab was pretty straightforward , configured interfaces and clients then configured EIGRP routing protocol. Routing protocols are needed to share routing information between routers so they will know how to reach a particular network when asked. EIGRP is a Cisco proprietary meaning it will only work with Cisco routers.
I created an Autonomous system of 51 and created an instance of it on each router with their corresponding networks. For example on Corp Router:
Corp(config)# router eigrp 51
Corp(config-router)# network 10.1.1.0 0.0.0.255
Corp(config-router)# network 10.1.2.0 0.0.0.3
Corp(config-router)# network 10.1.3.0 0.0.0.3
Corp(config-router)# network 10.1.4.0 0.0.0.3
Corp(config-router)# network 10.1.5.0 0.0.0.3
Corp(config-router)# no auto-summary
The lab in this book made all networks /24 (253 usable hosts), I went ahead and made links between routers /30 (2 usable hosts), taking advantage of EIGRP ability to do VLSM.
Using wildcard masks , I was able to clarified a particular VLSM subnet instead of its classful boundary.
Correct= 0.0.0.3 -> 255.255.255.252
Wrong= 10.1.1.0 -> 255.0.0.0
Wild cards don't automatically fix the auto-summary nature of EIGRP because EIGRP does auto-summary by default; we must disable it if we want to use discontiguous networks.
Corp(config-router)# no auto-summary
EIGRP uses three tables to maintain neighbors and routes, topology table, neighbor table and route table.
Neighbor Table contains information it has gather from adjacent neighbors including interface and address of the neighbor, along with sequence numbers to pack acknowledge update packets. This table in stored in RAM. Below is an output from my lab of the table. H in the table shows the order it which a neighbor was found.
Corp#show ip eigrp neighbors
IP-EIGRP neighbors for process 51
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.1.5.2 Fa0/0 10 00:35:46 40 1000 0 20
1 10.1.3.2 Se0/0/1 14 00:35:38 40 1000 0 23
2 10.1.2.2 Se0/0/0 10 00:35:37 40 1000 0 22
3 10.1.4.2 Se0/2/0 11 00:35:36 40 1000 0 18
*Note* IP is needed after the show command because EIGRP can support multiple protocols
Topology table contains destinations routes advised by neighbors per PDM using DUAL. PDM stands for protocol dependent module and it use to keep track of each protocol instance for EIGRP (IP, IPv6) DUAL is the Diffusing Update Algorithm used to calculate the best route and can determine the next best route if the best route goes down. The best route is called the feasible distance (FD) and the backup route to a network is called the feasible successor (FS), both which are stored in the topology table. Passive (P) means the route is being used while Active (A) means a route is being search for.
Corp#show ip eigrp topology
IP-EIGRP Topology Table for AS 51
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - Reply status
P 10.1.5.0/30, 1 successors, FD is 28160
via Connected, FastEthernet0/0
P 10.1.2.0/30, 1 successors, FD is 2169856
via Connected, Serial0/0/0
P 10.1.3.0/30, 1 successors, FD is 2169856
via Connected, Serial0/0/1
P 10.1.4.0/30, 1 successors, FD is 2169856
via Connected, Serial0/2/0
P 172.16.10.0/24, 1 successors, FD is 30720
via 10.1.5.2 (30720/28160), FastEthernet0/0
P 192.168.20.0/24, 2 successors, FD is 2172416
via 10.1.3.2 (2172416/28160), Serial0/0/1
via 10.1.2.2 (2172416/28160), Serial0/0/0
P 192.168.10.0/24, 2 successors, FD is 2172416
via 10.1.3.2 (2172416/28160), Serial0/0/1
via 10.1.2.2 (2172416/28160), Serial0/0/0
P 192.168.30.0/24, 1 successors, FD is 2172416
via 10.1.4.2 (2172416/28160), Serial0/2/0
P 192.168.40.0/24, 1 successors, FD is 2172416
via 10.1.4.2 (2172416/28160), Serial0/2/0
P 10.1.1.0/24, 1 successors, FD is 25625600
via Connected, Vlan1
Next post will be on into load balancing with EIGRP.
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