Cisco CCNA Exam Tutorial: IGRP And Equal Value Load Balancing
Cisco CCNA Exam Tutorial: IGRP And Equal Value Load Balancing
To move the CCNA examination, you've got to know the role of the bandwidth command with IGRP and EIGRP and when to use it. On this tutorial, we'll configure IGRP over a frame relay hub-and-spoke community utilizing the following networks:
R1 (the hub), R2, and R3 are working IGRP over the 172.12.123.0 /24 network. It is a T1 line.
R1 and R3 are also related on a special subnet, 172.12.13.0 /24. The bandwidth of this connection is 512 KBPS.
R2 and R3 are also related by an Ethernet phase, 172.23.0.zero /16.
We'll configure IGRP on R1, R2, and R3 with the router igrp 1 command. IGRP will run on all interfaces in the 172.12.0.zero and 172.23.0.zero network.
R1conf t
R1(config)router igrp 1
R1(config-router)community 172.12.0.0
The "1" in the router igrp command refers to the Autonomous System (AS). IGRP is a classful routing protocol, so wildcard masks are usually not used within the community statements.
R2conf t
R2(config-if)router igrp 1
R2(config-router)network 172.12.0.0
R2(config-router)community 172.23.0.zero
R3conf t
R3(config-if)router igrp 1
R3(config-router)network 172.12.0.zero
R3(config-router)network 172.23.0.zero
Run present ip route on R1. R1 will see three equal-value paths to the Ethernet network. IGRP helps load-sharing over as much as 4 equal-value paths by default, so all three paths appear in the routing table. R1 may also see a path to the loopback address on R2 and routes to the loopback tackle on R3. (It's also possible to run present ip route igrp with a view to see solely the IGRP routes.)
R1show ip route igrp
I 172.23.0.0/16 [100/8576] through 172.12.123.2, 00:00:02, Serial0
[100/8576] by way of 172.12.13.3, 00:00:02, Serial1
[100/8576] through 172.12.123.3, 00:00:01, Serial0
Keep in mind that the numbers within the brackets following the community number within the routes are the Administrative Distance and the IGRP metric, in that order.
Notice that classful masks are in use. IGRP does not help variable-length subnet masks (VLSM).
There are serial connections between R1 and R3. IGRP is assuming that each lines are T1 strains, running at 1544 KBPS. The 172.12.13.0 community is collaborating in equal-value load sharing because of IGRP's bandwidth assumption - that every one serial interfaces are linked to T1 lines.
To give IGRP an extra accurate image of the community's bandwidth, configure bandwidth 512 on R1 and R3's Serial1 interface (the interfaces on the 172.12.13.0 network).
R1conf t
R1(config)interface serial1
R1(config-if)bandwidth 512
R3conf t
R3(config)interface serial 1
R3(config-if)bandwidth 512
IGRP's assumption that every one serial lines run at 1544 KBPS is overridden by the bandwidth 512 command. IGRP now believes this line runs at 512 KBPS.
To see the impact of this command, clear your routing table on R1.
R1clear ip route *
R1show ip route igrp
I 172.23.0.0/16 [100/8576] through 172.12.123.three, 00:00:24, Serial0/zero
[100/8576] via 172.12.123.2, 00:00:17, Serial0/0
The routing table is cleared with clear ip route *. To see only the routes obtained in IGRP updates as a substitute of your entire desk, run present ip route igrp.
One of the paths to 172.23.0.0 is now gone - the route that went by means of the 172.12.13.0 network. Now that IGRP sees that link as slower than the others, equal-value load balancing is not going to happen over the 172.12.13.zero network.
It's necessary to understand that the bandwidth command does not truly change the bandwidth of the connection; it changes IGRP's assumption of what the bandwidth is.
Within the subsequent part of this IGRP load-balancing tutorial, we'll check out how one can configure unequal-cost load balancing.
As a CCNA candidate, you almost certainly have some background in PC hardware and workstation support. If that's the case, you're already conversant in loopback interfaces, significantly 127.0.0.1, the loopback address assigned to a PC.
Whenever you're studying all about the completely different physical interfaces in your CCNA exam - serial, ethernet, and BRI, amongst others - there's one logical interface it's worthwhile to learn about, and that is - you guessed it! - the loopback interface.
What is not as immediately obvious is why we use loopback interfaces on routers and switches to begin with. Many of the Cisco router features that can use loopbacks are intermediate and superior options that you'll learn about in your CCNP and CCIE studies, however these options all come back to one fundamental concept: If the loopback interface on a router is down, meaning the router is unavailable as a whole.
In distinction, a physical interface being down doesn't imply the router itself is out of commission. A router's ethernet port can go down, however the different bodily interfaces on that router are nonetheless operational. Since a loopback interface is logical, there's nothing bodily that may go incorrect with it.
As I discussed, you may learn completely different Cisco router and swap options that utilize loopback interfaces as you climb the Cisco certification ladder. There's one false impression about Cisco loopback interfaces that you simply need to get clear on now, though. You're probably accustomed to loopback interfaces on a PC, and may even know that the address vary 127.0.0.0 is reserved for loopback addressing.
Notice that this reserved deal with vary doesn't apply to loopbacks on Cisco gadgets, however. Should you try and assign an handle from this range to a Cisco loopback interface, you get this outcome:
R1conf t
Enter configuration commands, one per line. Finish with CNTL/Z.
R1(config)interface loopback0
R1(config-if)ip deal with 127.0.0.2 255.255.255.0
Not a sound host deal with - 127.0.0.2
R1(config-if)ip deal with 127.1.1.1 255.255.255.0
Not a valid host handle - 127.1.1.1
The range 127.0.0.0 is reserved for host loopbacks (akin to PCs), not routers or switches. Probably the most generally used address from this range is 127.0.0.1 - in the event you can't ping that on a workstation, meaning you possibly can't ping yourself, which implies there's a problem with the TCP/IP set up itself.
Keep these details in thoughts on the examination and within the workplace, and you're on your method to CCNA exam
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