EIGRP on sub interfaces - split horizon

[John Peterson]

I have come across a network which is use sub interfaces for their links to form relationship with router, would we need to disable split horizon on the interface as we also have other relationships from the same physical interface but different sub interface. From the school days I was always told to disable split horizon with updates would go out the same interface. But they did not mention if it matter to be a physical or sub interface?

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[smitesh kharecha]

Hi John,

Yes you need to disable split-horizon.

It would be on main physical interface.

Regards,

Smitesh

[Richard Burts]

I do not agree with Smitesh. As far as EIGRP is concerned different subinterfaces are different interfaces. There is no need to disable split horizon if your router is configured with multiple subinterfaces.

HTH

Rick

[Alessio Andreoli]

Hi,
I agree with Rick. EIGRP does not have any issue with sub interfaces and split horizon. That could be more an ospf issue over a FR network on a multipoint configuration

Alessio

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[cadet alain]

Hi Alessio,

talking about OSPF here may be a little bit ambiguous for the OP because he might think that split-horizon is part of OSPF which it ain't as it is purely a distance-vector feature.

EDIT: split-horizon is implemented in OSPF but only for LSAs for not advertising back in backbone area a LSA advertised into a non backbone area.

  but i consider that it is a special case and that it doesn't relate to split-horizon in distance vector protocols.

Regards.

Alain

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[Julio Carvajal]

Hello John,

Do not worry for split-horizon on this scenario as you are running over a completely different interface ( Sub-interface).

You should worry about if you were receiving the EIGRP updates on the same sub-interface where it needs to go out.

In your case it will take another road,

Regards,

Julio