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frame relay mutlipoint subint.+RIP

hi,

i configured a FR multipoint subinterface to participate in RIP process. however i learned that, in this situation, split horizon rules prevent routing updates from being sent and received correctly. what should i do?

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: frame relay mutlipoint subint.+RIP

I believe that Ankur's response is suggesting configuring multiple point to point subinterfaces. While I would agree that in most cases this is the optimum solution, I believe that this misses the point of the original post. He specifically asked about configuring a multipoint subinterface and using RIP. In this situation split horizon is an issue. The solution is to manually turn of split horizon (no ip split-horizon configured on the subinterface). This will work and will allow RIP updates learned from one neighbor to be advertised to other neighbors on that subinterface. Be aware that when you turn off split horizon that you have removed one of the mechanisms that RIP uses to prevent routing loops and that you now have some potential exposure to this problem. So do it carefully - but you can do it.

HTH

Rick

3 REPLIES
Cisco Employee

Re: frame relay mutlipoint subint.+RIP

Hi Shadow,

Configuring Frame Relay subinterfaces ensures that a single physical interface is treated as multiple virtual interfaces. This capability enables us to overcome split horizon rules. Packets received on one virtual interface can now be forwarded out another virtual interface, even if they are configured on the same physical interface.

HTH

Ankur

Hall of Fame Super Silver

Re: frame relay mutlipoint subint.+RIP

I believe that Ankur's response is suggesting configuring multiple point to point subinterfaces. While I would agree that in most cases this is the optimum solution, I believe that this misses the point of the original post. He specifically asked about configuring a multipoint subinterface and using RIP. In this situation split horizon is an issue. The solution is to manually turn of split horizon (no ip split-horizon configured on the subinterface). This will work and will allow RIP updates learned from one neighbor to be advertised to other neighbors on that subinterface. Be aware that when you turn off split horizon that you have removed one of the mechanisms that RIP uses to prevent routing loops and that you now have some potential exposure to this problem. So do it carefully - but you can do it.

HTH

Rick

Silver

Re: frame relay mutlipoint subint.+RIP

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