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Frame Relay Hub-Spoke and Split Horizon September 19, 2008

Posted by ZoeL in Cisco.
Tags: , , ,

Frame-relay Hub-Spoke dan Split Horizon.
Sebagai contoh 3 buah router terkoneksi ke switching Frame-Relay. Router Hub menjadi jembatan penghubung dua buah router yang berfungsi sebagai spoke.

Problem adalah, ketika routing dynamic diaktifkan, secara default routing dinamik memiliki fitur pencegah loop yang aktif mengawasi setiap interface. Fitur ini disebut Split Horizon. Ketika Split horizon melihat ada route advertisement yang di kirim dan di terima di inteface yang sama, split horizon berasumsi terjadi looping dan advertisement akan di stop. Ini tentu bermasalah ketika kita mengaplikasikan topology network berbentuk Frame Relay Hub-Spoke.

Router yang menjadi Hub tidak memperbolehkan 2 router spoke untuk berkomunikasi, karena router melihat advertisement yang dikirim ternyata kembali lagi ke interface yang sama. Untuk mencegah hal ini, tambahkan “no ip split-horizon” interface ke arah router spoke.

Untuk Routing EIGRP, split horizon bisa dimatikan per-interface. Sedangkan Routing RIP, split horizon hanya bisa dimatikan per proses routing.

Sedikit catatan tambahan dari milis:

The main things to remember with split horizon:

1) You should remember that physical FR interface has “ip split-horizon”
enabled by default. Pay attention to this with RIP configurations.

2) EIGRP has different command for split horizon; it is on by default
on every interface

3) You need to disable split-horizon if you want to advertise secondary IP
back the same interface.

4) A way to work out H&S problem w/ split-horizon is update unicasting.

5) Split-horizon applies to redistributed routes. That is, if if you receive
via one interface and try send them back the same interface,
redistibuting into
another protocol, you need to disable split horizon. Protocols need to
distance-vector, of course 🙂

6) Split-horizon is turned on for RIPng on every inteface by default. You
can disable it only per-process.

Take a look at the docCD on what split-horizon does, by disallowing
advertising what it receives on an interface to be sent out the same
interface. So if you are on hub and spoke, for example, and need to get
the inform from a spoke to another spoke (received at the hub, set up as
multipoint)….you will need to disable it




1. Matt Hanson - September 19, 2008

Good writing. Keep up the good work. I just added your RSS feed my Google News Reader..

Matt Hanson

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