Frame Relay - Split Horizon. Do they forward route update by default or not?
vazurahan
Member Posts: 23 ■□□□□□□□□□
in CCNA & CCENT
It says on this Cisco page that "IP split horizon checking is disabled by default for Frame Relay encapsulation, so routing updates come in and out the same interface."
Comprehensive Guide to Configuring and Troubleshooting Frame Relay [Frame Relay] - Cisco Systems
It says on the Todd Lammle book that you have to use point-to-point Interfaces to resolve Split Horizon issues.
I'm guessing if you received routing update on a physical or multi-point interface then it won't forward it back to that same interface. So what does "IP split horizon checking is disabled by default for Frame Relay encapsulation, so routing updates come in and out the same interface." mean?
Comprehensive Guide to Configuring and Troubleshooting Frame Relay [Frame Relay] - Cisco Systems
It says on the Todd Lammle book that you have to use point-to-point Interfaces to resolve Split Horizon issues.
I'm guessing if you received routing update on a physical or multi-point interface then it won't forward it back to that same interface. So what does "IP split horizon checking is disabled by default for Frame Relay encapsulation, so routing updates come in and out the same interface." mean?
Comments
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SharkDiver
Member Posts: 844
Good question.
I am not really sure what is meant by that.
I found the same phrase on Cisco's website here:
Frame Relay Frequently Asked Questions [Frame Relay] - Cisco Systems
Do they maybe mean that Split Horizon is disabled for routing updates, but not for actual data packets?
Either way, pay attention to what they say about EIGRP. Apparently, Split Horizon needs explicitly disabled for EIGRP.
Anyone else able to shed some light on this? -
Monkerz
Member Posts: 842
I believe split horizon is disabled by default on a physical interface, but subinterfaces have it enabled by default which would require 'no ip split-horizon'.