Cisco CCNA Exam Tutorial: IGRP And Equal Cost Load Balancing
To skip the CCNA examination, you’ve bought to comprehend the role of the bandwidth command with IGRP and EIGRP and while to exploit it. In this instructional, we’ll configure IGRP over a frame relay hub-and-spoke community utilising the subsequent networks:
R1 (the hub), R2, and R3 are going for walks IGRP over the 172.12.123.zero /24 network. This is a T1 line.
R1 and R3 are also connected on a distinctive subnet, 172.12.thirteen.zero /24. The bandwidth of this connection is 512 KBPS.
R2 and R3 are also attached through an Ethernet section, 172.23.0.zero /sixteen.
We’ll configure IGRP on R1, R2, and R3 with the router igrp 1 command. IGRP will run on all interfaces within the 172.12.zero.zero and 172.23.zero.zero community.
R1#conf t
R1(config)#router igrp 1
R1(config-router)#network 172.12.0.zero
The 1 in the router igrp command refers back to the Autonomous System (AS). IGRP is a classful routing protocol, so wildcard mask don't seem to be used inside the community statements.
R2#conf t
R2(config-if)#router igrp 1
R2(config-router)#community 172.12.zero.zero
R2(config-router)#network 172.23.zero.0
R3#conf t
R3(config-if)#router igrp 1
R3(config-router)#network 172.12.zero.0
R3(config-router)#community 172.23.0.0
Run educate ip course on R1. R1 will see three equivalent-expense paths to the Ethernet community. IGRP helps load-sharing over up to 4 equivalent-cost paths by default, so all three paths appear within the routing table. R1 may even see a course to the loopback handle on R2 and two routes to the loopback tackle on R3. (You might also run convey ip direction igrp so we can see best the IGRP routes.)
R1#convey ip course igrp
I 172.23.0.zero/16 [100/8576] thru 172.12.123.2, 00:00:02, Serial0
[one hundred/8576] by way of 172.12.13.three, 00:00:02, Serial1
[a hundred/8576] by means of 172.12.123.3, 00:00:01, Serial0
Remember that the numbers inside the brackets following the community wide variety within the routes are the Administrative Distance and the IGRP metric, in that order.
Note that classful masks are in use. IGRP does no longer support variable-length subnet mask (VLSM).
There are two serial connections between R1 and R3. IGRP is assuming that each traces are T1 traces, working at 1544 KBPS. The 172.12.thirteen.zero network is engaging in equivalent-charge load sharing by means of IGRPs bandwidth assumption – that every one serial interfaces are connected to T1 strains.
To supply IGRP a more right image of the networks bandwidth, configure bandwidth 512 on R1 and R3s Serial1 interface (the interfaces Click to find out more at the 172.12.thirteen.zero network).
R1(config)#interface serial1
R1(config-if)#bandwidth 512
R3(config)#interface serial 1
R3(config-if)#bandwidth 512
IGRPs assumption that every one serial lines run at 1544 KBPS is overridden by means of the bandwidth 512 command. IGRP now believes this line runs at 512 KBPS.
To see the impression of this command, clean your routing table on R1.
R1#clean ip route *
I 172.23.zero.zero/sixteen [100/8576] as a result of 172.12.123.3, 00:00:24, Serial0/0
[one hundred/8576] by the use of 172.12.123.2, 00:00:17, Serial0/0
The routing table is cleared with clean ip course *. To see purely the routes bought in IGRP updates in place of the comprehensive desk, run exhibit ip path igrp.
One of the trails to 172.23.0.0 is now long past – the course that went thru the 172.12.thirteen.zero network. Now that IGRP sees that hyperlink as slower than the others, identical-fee load balancing will now not happen over the 172.12.thirteen.0 network.
Its valuable to notice that the bandwidth command does not truly replace the bandwidth of the connection; it differences IGRPs assumption of what the bandwidth is.
In the subsequent portion of this IGRP load-balancing instructional, we’ll take a look at the way to configure unequal-settlement load balancing.