To move the CCNA examination, you've got to know the role of the bandwidth command with IGRP and EIGRP and when to make use of 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 additionally related on a different subnet, 172.12.13.0 /24. The bandwidth of this connection is 512 KBPS. R2 and R3 are also related by an Ethernet segment, 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.zero The "1" within the router igrp command refers to the Autonomous System (AS). IGRP is a classful routing protocol, so wildcard masks aren't used within the community statements. R2conf t R2(config-if)router igrp 1 R2(config-router)network 172.12.0.zero 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)community 172.23.0.zero Run present ip route on R1. R1 will see three equal-cost paths to the Ethernet network. IGRP supports load-sharing over up to four 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. (You can even run show ip route igrp to be able to see solely the IGRP routes.) R1show ip route igrp I 172.23.0.0/sixteen [100/8576] by way of 172.12.123.2, 00:00:02, Serial0 [100/8576] via 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 in the routes are the Administrative Distance and the IGRP metric, in that order. Notice that classful masks are in use. IGRP doesn't help variable-size subnet masks (VLSM). There are two serial connections between R1 and R3. IGRP is assuming that both lines are T1 strains, running at 1544 KBPS. The 172.12.13.0 community is participating in equal-value load sharing because of IGRP's bandwidth assumption - that every one serial interfaces are related to T1 lines. To give IGRP a more correct image of the community's bandwidth, configure bandwidth 512 on R1 and R3's Serial1 interface (the interfaces on the 172.12.13.zero 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 each one serial traces 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 desk 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] through 172.12.123.2, 00:00:17, Serial0/0 The routing table is cleared with clear ip route *. To see solely the routes acquired in IGRP updates as a substitute of your complete desk, run present ip route igrp. One of the paths to 172.23.0.0 is now gone - the route that went by way of the 172.12.13.0 network. Now that IGRP sees that link as slower than the others, equal-value load balancing won't happen over the 172.12.13.zero network. It's necessary to understand that the bandwidth command does not actually change the bandwidth of the connection; it adjustments IGRP's assumption of what the bandwidth is. Within the subsequent part of this IGRP load-balancing tutorial, we'll check out find out how to configure unequal-price 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 deal with 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 is advisable find out 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 idea: If the loopback interface on a router is down, that means the router is unavailable as a whole. In contrast, 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 will be taught 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 want to get clear on now, though. You're most likely accustomed to loopback interfaces on a PC, and may even know that the deal with vary 127.0.0.zero is reserved for loopback addressing. Note that this reserved deal with vary doesn't apply to loopbacks on Cisco units, however. If you try and assign an handle from this range to a Cisco loopback interface, you get this end result: 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 handle 127.1.1.1 255.255.255.0 Not a sound host tackle - 127.1.1.1 The range 127.0.0.0 is reserved for host loopbacks (comparable to PCs), not routers or switches. Probably the most generally used deal with from this vary is 127.0.0.1 - when you can't ping that on a workstation, meaning you possibly can't ping yourself, which suggests 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 way to CCNA exam
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To get your CCNA, you've got to know easy methods to configure equal cost load balancing. Learn all about it from Chris Bryant, CCIE 12933.
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