The Big show and Big D

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Configuring IGRP

Configuring basic IGRP is a two-step process. Configuring IGRP calls for the definition of an autonomous system (AS). By definition, an autonomous system is a set of routers under a single administrative technical authority. IGRP, EIGRP, and BGP all use the concept of autonomous systems, but BGP is the only routing protocol that actually utilizes the AS in routing decisions. It is not required to have a registered AS when configuring IGRP or EIGRP.

This following two-step process can be followed by an optional third step to fine-tune IGRP to specific environments:

Step 1. Enable IGRP and define an autonomous system on the router. This is accomplished with the router igrp autonomous_system_id global command.

Step 2. Add the networks that you want to run IGRP on. This is accomplished with the network a.b.c.d command from the config-router# mode. When you enter the network statements, it is necessary to enter only the major class boundary.

Step 3. Optional: Fine-tune IGRP metrics with bandwidth statements, or configure IGRP timers and options.

Example 10-1 illustrates the IGRP configuration from Figure 10-1.

Example 10-1 IGRP Configuration
  ! hostname igrp_rtr   !    router igrp 2001 graphics/u2190.gif IGRP routing process     network 172.16.0.0 graphics/u2190.gif Networks running IGRP     network 172.18.0.0    network 206.191.241.0   !   ip classless   ip default-network 206.191.241.0 graphics/u2190.gif Default Network   !  

Before moving on to configuring other IGRP options, let's take a look at the "Big D" and the "Big show" commands for IGRP.

The "Big show" and "Big D" for IGRP

Troubleshooting IGRP is similar to troubleshooting RIP. Most of the configuration errors around IGRP involve a bad network statement, discontinuous subnets, or inconsistent bit masks across the IGRP domain. The following is list of what I find to be the most useful show and debug commands for IGRP.

  • show ip protocols [ summary ]

  • Router#show ip route

  • Router(config-router)#debug ip igrp [ transactions events ]

The sections that follow explain these commands in greater detail.

show ip protocols [summary] Command

This command displays all routing protocols, detailed timer and metric information, as well as routing update information. Example 10-2 lists the output of the show ip protocols command.

Example 10-2 Output of the show ip protocols Command
 igrp_rtr#  show ip protocols   Routing Protocol is "igrp 2001" graphics/u2190.gif AS number   Sending updates every 90 seconds, next due in 19 seconds graphics/u2190.gif Update Timer   Invalid after 270 seconds, hold down 280, flushed after 630 graphics/u2190.gif Other 3 timers  Outgoing update filter list for all interfaces is   Incoming update filter list for all interfaces is   Default networks flagged in outgoing updates   Default networks accepted from incoming updates  IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 graphics/u2190.gif Metrics  IGRP maximum hopcount 100   IGRP maximum metric variance 1   Redistributing: igrp 2001  Routing for Networks: graphics/u2190.gif Networks IGRP is routing for  172.16.0.0     172.18.0.0     206.191.241.0  Routing Information Sources: graphics/u2190.gif Networks reporting routes  Gateway         Distance      Last Update     172.18.1.55          100      00:00:29     206.191.241.42       100      00:00:06     172.18.1.7           100      00:01:06     172.16.2.4           100      00:38:38     172.16.1.1           100      00:50:01  Distance: (default is 100) graphics/u2190.gif Administrative Distance  igrp_rtr# 
show ip route Command

This command lists the router's current routing table and the one that it uses to make forwarding decisions. The output lists what routing protocol the route is from ”in this case, I for IGRP. The number behind the route is the administrative distance of the route followed by the composite metric of IGRP. The via field explains who the route is from, how long ago an update was received, and by what interface it was received. Example 10-3 lists the output of the show ip route command. In this example, the route 206.191.241.0/24 is the default route, marked by the *. It has an administrative distance of 100 and a composite metric of 1200. The IGRP neighbor informing the router about the route is 172.18.1.5. The last update about the route occurred 52 seconds ago, through the Ethernet 0 port.

Example 10-3 show ip route Command Output
 r7#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is 172.18.1.5 to network 206.191.241.0  I*   206.191.241.0/24 [100/1200] via 172.18.1.5, 00:00:52, Ethernet0  I    172.16.0.0/16 [100/1200] via 172.18.1.5, 00:00:53, Ethernet0      172.18.0.0/24 is subnetted, 3 subnets I       172.18.18.0 [100/1600] via 172.18.1.55, 00:00:29, Ethernet0 C       172.18.19.0 is directly connected, Loopback20 C       172.18.1.0 is directly connected, Ethernet0 r7# 
Router(config-router)#debug ip igrp [ transactions events ] Command

The debug ip igrp transactions command shows detailed information about the routing updates being sent and received by the various interfaces. The debug ip igrp transactions command provides comprehensive routing detail, listing the networks and composite metric of each network. Both the commands show which interfaces are sending and receiving routes. The debug ip igrp events command provides only what type of routes are being advertised and received. Example 10-4 lists the output of the debug ip igrp transactions command, whereas Example 10-5 lists the output of debug ip igrp events. Use Figure 10-1 as reference for this output, which was performed on the igrp_router.

Example 10-4 debug ip igrp transactions Command Output
 01:40:07: IGRP: received update from 206.191.241.42 on Ethernet0 01:40:07:       network 172.16.0.0, metric 1121211 (neighbor 1121111) 01:40:27: IGRP: sending update to 255.255.255.255 via Ethernet0 (206.191.241.46) 01:40:27:       network 172.16.0.0, metric=1100 01:40:27:       network 172.18.0.0, metric=1100 01:40:27: IGRP: sending update to 255.255.255.255 via Ethernet1 (172.18.1.5) 01:40:27:       network 172.16.0.0, metric=1100 01:40:27:       exterior 206.191.241.0, metric=1100 01:40:27: IGRP: sending update to 255.255.255.255 via Ethernet3 (172.16.2.5) 01:40:27:       subnet 172.16.1.0, metric=1100 01:40:27:       network 172.18.0.0, metric=1100 01:40:27:       exterior 206.191.241.0, metric=1100 01:40:27: IGRP: sending update to 255.255.255.255 via Ethernet5 (172.16.1.5) 01:40:27:       subnet 172.16.2.0, metric=1100 01:40:27:       network 172.18.0.0, metric=1100 01:40:27:       exterior 206.191.241.0, metric=1100 igrp_rtr# 
Example 10-5 debug ip igrp events Command Output
 02:52:53: IGRP: sending update to 255.255.255.255 via Ethernet0 (206.191.241.46) 02:52:53: IGRP: Update contains 0 interior, 2 system, and 0 exterior routes. 02:52:53: IGRP: Total routes in update: 2 02:52:53: IGRP: sending update to 255.255.255.255 via Ethernet1 (172.18.1.5) 02:52:53: IGRP: Update contains 0 interior, 1 system, and 1 exterior routes. 02:52:53: IGRP: Total routes in update: 2 02:52:53: IGRP: sending update to 255.255.255.255 via Ethernet3 (172.16.2.5) 02:52:53: IGRP: Update contains 1 interior, 1 system, and 1 exterior routes. 02:52:53: IGRP: Total routes in update: 3 02:52:53: IGRP: sending update to 255.255.255.255 via Ethernet5 (172.16.1.5) 02:52:53: IGRP: Update contains 1 interior, 1 system, and 1 exterior routes. 02:52:53: IGRP: Total routes in update: 3 02:52:55: IGRP: received update from 172.18.1.7 on Ethernet1 02:52:55: IGRP: Update contains 1 interior, 0 system, and 0 exterior routes. 02:52:55: IGRP: Total routes in update: 1 
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CCIE Practical Studies, Volume I
CCIE Practical Studies, Volume I
ISBN: 1587200023
EAN: 2147483647
Year: 2001
Pages: 283
Authors: Karl Solie

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