Tunnel Source

Answered Question
Jan 15th, 2009

Hi,

In a regualr gre point to point tunnel, what happens when you set the tunnel source to a loopback?

Thanks,

Richard

I have this problem too.
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Correct Answer by Joseph W. Doherty about 7 years 10 months ago

Yes, the loopback would become the tunnel's souce "egress", but it works like when we use loopbacks for other source addresses on the router. Traffic would flow across what it considers to be the best physical path physical interface toward tunnel's destination.

Correct Answer by Paolo Bevilacqua about 7 years 10 months ago

Nothing bad, it's actually the correct way to identify a router uniquely and independently for interfaces and their status.

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Correct Answer
Paolo Bevilacqua Thu, 01/15/2009 - 17:11

Nothing bad, it's actually the correct way to identify a router uniquely and independently for interfaces and their status.

richard.m.gilbert Fri, 01/16/2009 - 04:42

Thanks for the response. But, what actually happens with that. I guess I have misunderstood that command because I thought that when you applied the tunnel source ___ command that what ever interface put in that command would be the egress interface. I now realize that I must be wrong with that and am kinda confused about exactly what that command does now.

Richard

Correct Answer
Joseph W. Doherty Fri, 01/16/2009 - 05:24

Yes, the loopback would become the tunnel's souce "egress", but it works like when we use loopbacks for other source addresses on the router. Traffic would flow across what it considers to be the best physical path physical interface toward tunnel's destination.

richard.m.gilbert Fri, 01/16/2009 - 07:18

Thanks. So if I put in the tunnel source as fa0/0 and that interface goes down (physically or logically) then the tunnel doesn't have the flexibility to go out another port?

Joseph W. Doherty Fri, 01/16/2009 - 08:04

I believe that's true.

Of course, using a loopback for the tunnel source won't help you if there's only one physical path for the tunnel and that's the interface that's failed.

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