Cisco CCNA CCNP Certification Exam Lab: Frame Relay Subinterfaces And Split Horizon Computers Articles | July 24 Jon Flanagan Liverpool Jersey , 2006
To truly understand Frame Relay subinterfaces and split horizon, you've got to see both in action. Study for your exam and prepare for success with this fully illustrated lab from Chris Bryant, CCIE #12933.
Earning your Cisco CCNA and CCNP is a tough proposition, and part of that is the fact that you quickly learn that there?s usually more than one way to do things with Cisco routers ? and while that?s generally a good thing Joel Matip Liverpool Jersey , you better know the ins and outs of all options when it comes to test day and working on production networks. Working with Frame Relay subinterfaces and split horizon is just one such situation.
One reason for the use of subinterfaces is to circumvent the rule of split horizon. You recall from your CCNA studies that split horizon dictates that a route cannot be advertised out the same interface upon which it was learned in the first place. In the following example, R1 is the hub and R2 and R3 are the spokes. All three routers are using their physical interfaces for frame relay connectivity, and they are also running RIPv2 172.12.123.0 24. Each router is also advertising a loopback interface, using the router number for each octet.
R 1.1.1.1 [1201] via 172.12.123.1, 00:00:04, Serial0
The hub router R1 has a route to both loopbacks Emre Can Liverpool Jersey , but neither spoke has a route to the other spoke's loopback. That's because split horizon prevents R1 from advertising a network via Serial0 if the route was learned on Serial0 to begin with.
We've got two options here, one of which is to disable spilt horizon on the interface. While doing so will have the desired effect in our little network, disabling split horizon is not a good idea and should be avoided whenever possible. We?re not going to do it in this lab, but here is the syntax to do so:
R1(config)#interface serial0
R1(config-if)#no ip split-horizon
A better solution is to configure subinterfaces on R1. The IP addressing will have to be revisited Dominic Solanke Liverpool Jersey , but that's no problem here. R1 and R2 will use 172.12.123.0 24 to communicate, while R1 and R3 will use 172.12.13.0 24. R3's serial0 interface will need to be renumbered, so let's look at all three router configurations:
R3(config-if)#frame map ip 172.12.13.1 321 broadcast
R3(config-if)#frame map ip 172.12.123.2 321 broadcast
A frame map statement always names the REMOTE IP address and the LOCAL DLCI. Don't forget the broadcast option!
Show frame map shows us that all the static mappings on R1 are up and running. Note the "static" output, which indicates these mappings are a result of using the frame map command. Pings are not shown Divock Origi Liverpool Jersey , but all three routers can ping each other at this point.
R1#show frame map
Serial0 (up): ip 172.12.123.2 dlci 122(0x7A,0x1CA0), static,
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