Exam: 640-802
Exam Objective: Configure, verify, and troubleshoot EIGRP
Contents
- Introduction
- Technology Background
- Lab Scenario
- Lab Objectives
- Lab Solution
Introduction
EIGRP is a Cisco proprietary enhanced distance vector (hybrid) routing protocol. It is a classless protocol which sends output updates at startup and when there is a change in the network. The maximum hop count for EIGRP is 255. It supports various Routed protocols such as IPv4, IPv6, Appletalk, etc. It uses proprietary Reliable Transport Protocol (RTP) to send updates and Diffusing Update Algorithm (DUAL) to find the best path.Technology Background
EIGRP is started on a router using the "router eigrp <as>" command. AS stands for Autonomous system.AS defines an EIGRP network. Routers belonging to different Autonomous Systems do not share routing information.Once EIGRP has been started, network can be defined using the "network <address> <wildcard mask>". Wildcard mask is optional if you are using default subnet mask for the address class.
As soon as the network statement is added, EIGRP will start on interface which belongs to the Network configured with the network command. EIGRP will start sending out Hello packets to multicast address 224.0.0.10 to discover neighboring routers running EIGRP.
If it receives an ACK or Hello from another router in the same EIGRP AS then it will form an adjacency with it and the routers will exchange their full routing table.
EIGRP maintains a table of all its neighbors. This table can be viewed using the "show ip eigrp neighbor" command.
Routes received from neighbors are stored in a local topology table.
The route received from the neighbor will have a metric attached to it. This is the metric that is applicable on the advertising router. This is called the Reported Distance (RD). The receiving route will need to add the metric of the link between itself and the advertising router. If multiple paths are learned to a remote network then the path with best metric (RD + metric to the advertising router) is selected. This metric is the Feasible Distance (FD).
The path with the best metric is called the Successor. This is the route which will be presented to the router for the routing table. All other route to the same remote network will be kept as Feasible Successors as long as their RD is lower than the FD. Feasible successor is the route which will be used when the Successor is lost. EIGRP will keep upto 6 successors in the topology table.
EIGRP uses a combination of Bandwidth, Delay, Load and Reliability to calculate the metric of a route. Metric is the cost of using that route.
EIGRP topology table can be viewed using "show ip eigrp topology" command.
An important thing to note about EIGRP communication between two routers is that it is done using a Multicast to 224.0.0.10 IP address. If a route does not get Hellos from an adjacent router for a configured period then it will remove it from its neighbor table and also remove all routes learned from it.
Similarly if an EIGRP update is not acknowledged by an adjacent neighbor then update will be resent using a unicast packet up to 16 times. If the adjacent router still fails to acknowledge the update then the adjacency will be torn down and all routes learned from that neighbor will be flushed.
We learned previously that EIGRP will select the route with the best metric. What if there are multiple routes to the same destination with the same metric? EIGRP can load-balance over a maximum of 6 such equal cost paths. By default it is configured to load balance between 4 paths. This can be changed using the following command:
Router(config)#router eigrp 1
Router(config-router)#maximum-paths 6
As mentioned earlier EIGRP has a maximum hop count of 255 but the default maximum hop count is 100. This can be changed using the following command:
Router(config)#router eigrp 1
Router(config-router)#metric maximum-hops 255
The number 255 can be anything from 1 to 255.
EIGRP can be disabled on an interface using the "passive-interface <interface>" command in the EIGRP configuration mode. This will stop EIGRP from sending and receiving Hello packets on an interface. This means that EIGRP will not for adjacency on that interface and hence will not send or receive routes.
Lab Scenario
We want to use EIGRP in the network shown in Figure 2. Your task is to configure EIGRP on all routers such that:- Traffic from 192.168.1.0/24 never goes through RouterC to reach 192.168.7.0/24
- RouterB never load-balances between the two paths to 192.168.7.0/24
- RouterA should not form adjacency if Hello packets are received on its fa0/1 interface
- RouterC and RouterD should not form adjacency if Hello packets are received on their fa0/2 interfaces.
Figure 2
Lab Objectives
- Configure EIGRP is AS 100 on all routers and advertise all connected routes
- Set maximum hop to 2 on RouterA
- Set maximum-paths to 1 on RouterB
- Configure fa0/1 as passive on RouterA
- Configure fa0/2 as passive on RouterC and RouterD
Lab Solution
First we need to enable EIGRP on all routers and advertise their connected routes:RouterA(config)#router eigrp 100
RouterA(config-router)#network 192.168.1.0
RouterA(config-router)#network 192.168.2.0
RouterB(config)#router eigrp 100
RouterB(config-router)#network 192.168.2.0
RouterB(config-router)#network 192.168.3.0
RouterB(config-router)#network 192.168.5.0
RouterC(config)#router eigrp 100
RouterC(config-router)#network 192.168.3.0
RouterC(config-router)#network 192.168.4.0
RouterC(config-router)#network 192.168.6.0
RouterD(config)#router eigrp 100
RouterD(config-router)#network 192.168.5.0
RouterD(config-router)#network 192.168.6.0
RouterD(config-router)#network 192.168.7.0
We need to ensure that traffic from 192.168.1.0/24 never cross RouterC on the way to 192.168.7.0/24. RouterB will have the path form RouterC as a feasible successor to 192.168.7.0/24. This path will be advertised to RouterA if RouterB's fa0/2 link goes down.
The difference between the two paths for RouterA is the hop count. If we restrict the hop count to 2 on RouterA then the path to 192.168.7.0/24 from RouterC will never be used because its hop count is higher.
RouterA(config)#router eigrp 100
RouterA(config-router)#metric maximum-hops 2
We can stop RouterB from load-balancing by setting maximum-paths to 1 instead of default 4 :
RouterB(config)#router eigrp 100
RouterB(config-router)#maximum-paths 1
Finally we can make the given interfaces passive by using the following commands:
RouterA(config)#router eigrp 100
RouterA(config-router)#passive-interface fa0/1
RouterC(config)#router eigrp 100
RouterC(config-router)#passive-interface fa0/2
RouterD(config)#router eigrp 100
RouterD(config-router)#passive-interface fa0/2
Let's verify configuration by looking at the routing table of each router:
RouterA#show ip route
--output truncated--
Gateway of last resort is not set
D 192.168.4.0/24 [90/309760] via 192.168.2.2, 00:01:59, FastEthernet0/0
D 192.168.5.0/24 [90/284160] via 192.168.2.2, 00:01:59, FastEthernet0/0
D 192.168.6.0/24 [90/309760] via 192.168.2.2, 00:01:59, FastEthernet0/0
D 192.168.7.0/24 [90/286720] via 192.168.2.2, 00:01:59, FastEthernet0/0
C 192.168.1.0/24 is directly connected, FastEthernet0/1
C 192.168.2.0/24 is directly connected, FastEthernet0/0
D 192.168.3.0/24 [90/307200] via 192.168.2.2, 00:01:59, FastEthernet0/0
RouterB#show ip route
--output truncated--
Gateway of last resort is not set
D 192.168.4.0/24 [90/284160] via 192.168.3.2, 00:02:12, FastEthernet0/1
C 192.168.5.0/24 is directly connected, FastEthernet0/2
D 192.168.6.0/24 [90/284160] via 192.168.5.2, 00:02:12, FastEthernet0/2
D 192.168.7.0/24 [90/30720] via 192.168.5.2, 00:02:12, FastEthernet0/2
D 192.168.1.0/24 [90/307200] via 192.168.2.1, 00:02:12, FastEthernet0/0
C 192.168.2.0/24 is directly connected, FastEthernet0/0
C 192.168.3.0/24 is directly connected, FastEthernet0/1
RouterC#show ip route
--output truncated--
Gateway of last resort is not set
C 192.168.4.0/24 is directly connected, FastEthernet0/2
D 192.168.5.0/24 [90/284160] via 192.168.3.1, 00:03:22, FastEthernet0/1
C 192.168.6.0/24 is directly connected, FastEthernet0/0
D 192.168.7.0/24 [90/284160] via 192.168.6.2, 00:03:21, FastEthernet0/0
D 192.168.1.0/24 [90/332800] via 192.168.3.1, 00:02:49, FastEthernet0/1
D 192.168.2.0/24 [90/307200] via 192.168.3.1, 00:03:22, FastEthernet0/1
C 192.168.3.0/24 is directly connected, FastEthernet0/1
RouterD#show ip route
--output truncated--
Gateway of last resort is not set
D 192.168.4.0/24 [90/284160] via 192.168.6.1, 00:03:35, FastEthernet0/0
C 192.168.5.0/24 is directly connected, FastEthernet0/1
C 192.168.6.0/24 is directly connected, FastEthernet0/0
C 192.168.7.0/24 is directly connected, FastEthernet0/2
D 192.168.1.0/24 [90/332800] via 192.168.5.1, 00:02:59, FastEthernet0/1
D 192.168.2.0/24 [90/307200] via 192.168.5.1, 00:03:35, FastEthernet0/1
D 192.168.3.0/24 [90/307200] via 192.168.6.1, 00:03:35, FastEthernet0/0
[90/307200] via 192.168.5.1, 00:03:35, FastEthernet0/1
We can further verify the configuration using "show ip protocols" command:
RouterA#sh ip protocols
Routing Protocol is "eigrp 100"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 2
EIGRP maximum metric variance 1
Redistributing: eigrp 100
EIGRP NSF-aware route hold timer is 240s
Automatic network summarization is in effect
Automatic address summarization:
192.168.1.0/24 for FastEthernet0/0
Maximum path: 4
Routing for Networks:
192.168.1.0
192.168.2.0
Passive Interface(s):
FastEthernet0/1
Routing Information Sources:
Gateway Distance Last Update
192.168.2.2 90 00:06:31
Distance: internal 90 external 170
RouterB#sh ip protocols
Routing Protocol is "eigrp 100"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 100
EIGRP NSF-aware route hold timer is 240s
Automatic network summarization is in effect
Automatic address summarization:
192.168.5.0/24 for FastEthernet0/0, FastEthernet0/1
192.168.3.0/24 for FastEthernet0/0, FastEthernet0/2
192.168.2.0/24 for FastEthernet0/1, FastEthernet0/2
Maximum path: 1
Routing for Networks:
192.168.2.0
192.168.3.0
192.168.5.0
Routing Information Sources:
Gateway Distance Last Update
192.168.3.2 90 00:07:25
192.168.2.1 90 00:07:26
192.168.5.2 90 00:07:26
Distance: internal 90 external 170
RouterC#show ip protocols
Routing Protocol is "eigrp 100"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 100
EIGRP NSF-aware route hold timer is 240s
Automatic network summarization is in effect
Automatic address summarization:
192.168.6.0/24 for FastEthernet0/1
192.168.4.0/24 for FastEthernet0/0, FastEthernet0/1
192.168.3.0/24 for FastEthernet0/0
Maximum path: 4
Routing for Networks:
192.168.3.0
192.168.4.0
192.168.6.0
Passive Interface(s):
FastEthernet0/2
Routing Information Sources:
Gateway Distance Last Update
192.168.3.1 90 00:09:16
192.168.6.2 90 00:09:16
Distance: internal 90 external 170
RouterD#show ip protocols
Routing Protocol is "eigrp 100"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 100
EIGRP NSF-aware route hold timer is 240s
Automatic network summarization is in effect
Automatic address summarization:
192.168.7.0/24 for FastEthernet0/0, FastEthernet0/1
192.168.6.0/24 for FastEthernet0/1
192.168.5.0/24 for FastEthernet0/0
Maximum path: 4
Routing for Networks:
192.168.5.0
192.168.6.0
192.168.7.0
Passive Interface(s):
FastEthernet0/2
Routing Information Sources:
Gateway Distance Last Update
192.168.5.1 90 00:10:08
192.168.6.1 90 00:10:08
Distance: internal 90 external 170
References:
Enhanced Interior Gateway Routing Protocol
http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml
Configuring EIGRP
http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfeigrp.html
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