Viewing the routing updates your router is sending and receiving is an invaluable tool. The fol-lowing debug commands will give you a step-by-step account of what is happening between your router and its neighbors.
Dallas#debug ip eigrp
IP-EIGRP Route Events debugging is on
16:04:19: IP-EIGRP: 10.10.10.0/24 - do advertise out Serial2/0.1 16:04:19: IP-EIGRP: 192.168.24.0/24 - do advertise out Serial2/0.1 16:04:19: IP-EIGRP: Int 192.168.24.0/24 metric 128256 - 256 128000 16:04:19: IP-EIGRP: Processing incoming UPDATE packet
16:04:19: IP-EIGRP: Int 20.20.20.0/24 M 1889792 - 1249792 640000 SM 128256 - ➥256 128000
16:04:19: IP-EIGRP: Int 20.20.20.0/24 metric 1889792 - 1249792 640000 16:04:19: IP-EIGRP: Processing incoming UPDATE packet
16:04:19: IP-EIGRP: Int 192.168.24.0/24 M 4294967295 - 1657856 4294967295 ➥SM 429 4967295 - 1657856 4294967295
The debug ip eigrp command allows you to view the routing updates sent between the router and its neighbors. The information contained is the routes and their corresponding met-ric the router has received along with what routes the router is going to send out and the inter-face that will advertise the route. Recall that the value 4,294,967,295 represents infinity for IGRP and EIGRP, thus an unreachable advertisement.
The debug eigrp packets command can be used to view the following types of packets sent between the router and its neighbors:
Hello
Update
Request
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Query
Reply
The update and query messages are all considered reliable EIGRP messages.
This means that the receiving router must send back an acknowledgment to the message.
Here’s an example of the output of the debug eigrp packets command:
Dallas#debug eigrp packets EIGRP Packets debugging is on
(UPDATE, REQUEST, QUERY, REPLY, HELLO, IPXSAP, PROBE, ACK, STUB, ➥SIAQUERY, SIAREPLY)
Dallas#
16:07:43: EIGRP: Received HELLO on Serial2/0.1 nbr 10.10.10.1
16:07:43: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ ➥un/rely 0/0
16:07:43: EIGRP: Sending HELLO on Loopback0
16:07:43: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 16:07:43: EIGRP: Received HELLO on Loopback0 nbr 192.168.24.1 16:07:43: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0
16:07:43: EIGRP: Packet from ourselves ignored 16:07:44: EIGRP: Sending HELLO on Serial2/0.1
16:07:44: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 16:07:47: EIGRP: Received HELLO on Serial2/0.1 nbr 10.10.10.1
16:07:47: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ ➥un/rely 0/0
You can also view the number of EIGRP packets sent and received on the router. The show ip eigrp traffic command displays the number of packets sent and received for each of these packet types:
Hello
Update
Query
Reply
ACKs
The next example shows the output for the show ip eigrp traffic command:
Dallas#show ip eigrp traffic
IP-EIGRP Traffic Statistics for process 100 Hellos sent/received: 632/622
Updates sent/received: 19/18
Summary 139
Queries sent/received: 0/0 Replies sent/received: 0/0 Acks sent/received: 8/11
There is one more command I’m going to explain. The show ip eigrp events command is an undocumented command. This command displays a log of every EIGRP event—when routes are injected and removed from the routing table and when EIGRP adjacencies reset or fail. This information can be used to see if there are routing instabilities in the network. Here’s an example of the output from this command:
Dallas#show ip eigrp events Event information for AS 100:
1 16:14:45.007 Poison squashed: 192.168.24.0/24 reverse 2 16:14:44.967 Change queue emptied, entries: 1
3 16:14:44.967 Metric set: 20.20.20.0/24 1889792 4 16:14:44.967 Update reason, delay: new if 4294967295 5 16:14:44.967 Update sent, RD: 20.20.20.0/24 4294967295 6 16:14:44.967 Update reason, delay: metric chg 4294967295 7 16:14:44.967 Update sent, RD: 20.20.20.0/24 4294967295 8 16:14:44.967 Route install: 20.20.20.0/24 10.10.10.1 9 16:14:44.967 Find FS: 20.20.20.0/24 4294967295 10 16:14:44.967 Rcv update met/succmet: 1889792 128256 11 16:14:44.967 Rcv update dest/nh: 20.20.20.0/24 10.10.10.1 12 16:14:44.967 Metric set: 20.20.20.0/24 4294967295
13 16:14:42.059 Peer up: 10.10.10.1 Serial2/0.1 14 16:14:39.963 Peer down end, handle: 0 15 16:14:39.963 NDB delete: 20.20.20.0/24 1
16 16:14:39.963 Poison squashed: 20.20.20.0/24 rt gone 17 16:14:39.963 RDB delete: 20.20.20.0/24 10.10.10.1 18 16:14:39.963 Not active net/1=SH: 20.20.20.0/24 0 19 16:14:39.963 FC not sat Dmin/met: 4294967295 1889792 20 16:14:39.963 Find FS: 20.20.20.0/24 1889792
21 16:14:39.963 Peer down: 10.10.10.1 Serial2/0.1
As I stated at the beginning of this section, there are many tools available for verifying and troubleshooting EIGRP. Remember, the tools covered here are not the only ones. I know all this information can be overwhelming at first, but with time and practice it will become second nature.
Summary
Was that some cool information or what? EIGRP is a Cisco proprietary routing protocol. Guess what that means? It means if you have a multi-vendor network, you’re probably not going to want to use EIGRP.
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So if you can’t use it in a multi-vendor environment, why would you want to use it at all? EIGRP provides the best of both distance-vector and link-state routing protocols. That’s right—EIGRP is a hybrid routing protocol. EIGRP, unlike other routing protocols, allows for unequal-cost load bal-ancing. That means that EIGRP can use multiple links to load balance information across, even if the links do not have the same cost.
Another big draw to EIGRP is its ease of configuration. When using EIGRP, you need to determine what autonomous system number you want to use. This number needs to be the same on all the routers you want sharing the routing information. Once you’ve made this determi-nation, you are ready to start configuring EIGRP.
In order to configure EIGRP, you first need to enable it on the device. Once you’ve enabled EIGRP on the device, you then need to specify the networks on the router you want participat-ing in EIGRP. It’s important to remember that the network statement in EIGRP doesn’t tell EIGRP which network to advertise. What the network statement does do is to tell EIGRP which interfaces to allow to participate in EIGRP. EIGRP then looks at the network address and mask that the interface belongs to and advertises that network address and mask.
Congratulations! You have now made it through EIGRP. EIGRP will be on the BSCI exam;
however, IGRP will not. Even though IGRP is not covered on the exam, it is still important to know in order to understand EIGRP. Remember, EIGRP is simply an enhancement to IGRP.
Exam Essentials
Know the key differences between IGRP and EIGRP. There are two key differences between IGRP and EIGRP: IGRP is a classful pure distance-vector routing protocol and EIGRP is a classless hybrid distance-vector routing protocol. Classful routing protocols do not send sub-net mask information in their routing updates, whereas classless routing protocols do send subnet mask information.
Understand how DUAL operates. When EIGRP learns the network topology, it will run the DUAL algorithm to determine the best route to a destination. This best route becomes the suc-cessor route. Other routes to the same destination that have an advertised distance less than the feasible distance of the successor route will become feasible successor routes. DUAL will not run again until all the routes to the destination are lost.
Understand how to configure EIGRP. One of the most attractive features of EIGRP is its ease of configuration. To configure EIGRP, you first need to enable it on the device with the router eigrp as# command. Next you need to specify the interfaces to participate in EIGRP with the network command. That’s all there is to basic EIGRP configuration.
Understand how to verify and troubleshoot proper operation of EIGRP. After the configu-ration of the network, you should be able to verify proper opeconfigu-ration of EIGRP. You can still use the standard verification commands such as show ip route and show ip protocols. In addi-tion to those commands, such EIGRP specific commands as show ip eigrp traffic and show ip egrp events can be used.