Physical or Virtual L3 interfaces

Unanswered Question
Jan 29th, 2009

Hi Folks,

Have a question that I hope you can help with.

Have two 6500 switches that are directly connected via a GigE Link.

Running OSPF between the switches. At layer 3 the switches

are connected via a point-to-point connection.

I am considering two configuration options

1. Connect the switches using a L2 trunk and use virtual

interfaces for the point-to-point L3 connection.

2. Make the physical interfaces on the switches L3

(NOT Switch ports).

My question is which option is fastest to detect a fault (and recover) at L3

when the circuit goes down?

What is the difference in the times for the options?

Hope you can help.

Best regards,


I have this problem too.
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Giuseppe Larosa Fri, 01/30/2009 - 04:55

Hello Phil,

I wouldn't expect very big difference in times but one aspect to be considered is the

msfc autostate feature

interface vlan X is seen as up/up until there is at least one L2 port that is in spanning tree forwarding state for L2 Vlan X.

So interface SVI VLAN X may be kept up by the fact that L2 Vlan X is carried on some other L2 trunk.

A routed point-to-point interface goes down when the link is down for sure.

On the other side the L3 adjacency can be rebuild after STP convergence if there is an alternate L2 path.

Hope to help


pbelletty Fri, 01/30/2009 - 07:10

Hi Guiseppe,

Thanks for the reply. That was extremely helpful.

Much appreciated.



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