Daniel Roesen dr at
Tue Feb 3 10:52:34 CET 2009

On Tue, Feb 03, 2009 at 10:35:26AM +0100, Alexander Gall wrote:
> No, I think Geoff did a "show interface tunnel" but that MTU is
> irrelevant, I think.

Oh indeed, I was thinking of "sh ip(v6) interface TunnelX".

I do see the same bogus MTU of 1514 on "physical" Tunnel interface
level as well (encaps GRE here, so it seems to be ).

> But beware, if that value is the same as the default derived from
> the egress interface, the "ipv6 mtu" statement does not appear in
> the configuration and the MTU changes dynamically when the egress
> interface changes (which can be a problem in certain cases).

Argh, I never saw this happen... need to lab that. Is that consistent
behaviour across all IOS?

IOS trying to be smart is harmful at best. :-(

Best regards,

CLUE-RIPE -- Jabber: dr at -- dr at IRCnet -- PGP: 0xA85C8AA0

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