Route Information

Route Information
As stated earlier, you will receive most of your information about the operation of IGRP from
the routing table. In order to view the routing table, you need to enter the following command
in privileged EXEC mode:
Router#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, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
C 192.168.24.0/24 is directly connected, Loopback0
I 20.0.0.0/8 [100/7382] via 10.10.10.1, 00:00:43, Serial2/0.1
10.0.0.0/24 is subnetted, 1 subnets
C 10.10.10.0 is directly connected, Serial2/0.1
As you can see from the routing table, we have one route learned via IGRP. You will know the
routes learned via IGRP from the code of I in front of the route entry. The routing table is a very
important verification and troubleshooting tool, because it informs you of all the routes that have
been learned via IGRP that were considered the best for their respective destination network. If a
route is not there that you believe should be there, you need to start troubleshooting.
Interior Gateway Routing Protocol 115
Once you have viewed the routing table, you can enter the following command, using the
appropriate routing entry, to view more detailed information about a particular route:
Router#show ip route 20.0.0.0
Routing entry for 20.0.0.0/8
Known via "igrp 100", distance 100, metric 7382
Redistributing via igrp 100
Advertised by igrp 100 (self originated)
Last update from 10.10.10.1 on Serial2/0.1, 00:00:03 ago
Routing Descriptor Blocks:
* 10.10.10.1, from 10.10.10.1, 00:00:03 ago, via Serial2/0.1
Route metric is 7382, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 2048 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 0
This command can give you details about a particular route. The most important information
you can learn from this command is the details of the composite metric for the particular
route. The command informs you what the minimum bandwidth, cumulative delay, reliability,
load, and minimum MTU are for the particular routing entry’s path to the destination network.
Recall that the metric is computed as
[(10000000 ÷ minimum bandwidth) + (cumulative delay ÷ 10)] = [(10000000 ÷ 2048) +
(25000 ÷ 10)] = 4882.8125 + 2500 = 7382
Note that fractional values are truncated, not rounded.
Routing Protocol Information
You can also view information that is specific to routing protocols. There are two ways in which
to view this information. The first way to view this information is at the global level of the
router. Entering the following command, in privileged EXEC mode, provides you with specific
information about all routing protocols on the router:
Router#show ip protocols
Routing Protocol is "igrp 100"
Sending updates every 90 seconds, next due in 71 seconds
Invalid after 270 seconds, hold down 280, flushed after 630
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
IGRP maximum hopcount 100
IGRP maximum metric variance 1
Redistributing: igrp 100
116 Chapter 4  IGRP and EIGRP
Routing for Networks:
10.0.0.0
192.168.24.0
Routing Information Sources:
Gateway Distance Last Update
10.10.10.1 100 00:00:49
Distance: (default is 100)
As you can see, the router in this example is running only IGRP. If it had been running other
routing protocols, you would have seen information about each of the routing protocols on the
router. This command gives you the values set for all of your timers and shows what routes this
particular router is advertising to its neighbors. For IGRP and EIGRP, it also gives you the values
for maximum hop count and variance.
As seen earlier in this chapter, the other way to view specific routing protocol information
is at the interface level. The most important information you will receive from the following
command, entered in privileged EXEC mode, is what the bandwidth, delay, reliability, load,
and MTU are for that particular interface:
Router#show interface serial 2/0.1
Serial2/0.1 is up, line protocol is up
Hardware is DSCC4 Serial
Internet address is 10.10.10.2/24
MTU 1500 bytes, BW 2048 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation FRAME-RELAY
All of the commands covered so far give information about IGRP on the particular router. This
is important information, but if a route is not there that should be, it might not give you all the
information you need. The next section covers how to monitor what your router is sending to its
neighbors and also what it is receiving from its neighbors.