[c-nsp] MTU settings/GRE tunnel

[Pavel Gulchouck]

  Hi,

On Thu, Sep 20, 2007 at 10:55:08AM +0100, Phil Mayers writes:
[...]
PM> So, ideally set your physical interface ip mtu to 1536, physical mtu to
PM> whatever IP overhead you have (e.g. 14 bytes on ethernet - 1550).

I set mtu on physical interface and on SVI to 4096, set
"ip mtu 1500" on gre tunnel but with no luck: MTU on tunnel
interface is 1514, and if I try to increase it router responses:
"% Interface Tunnel2 does not support adjustable maximum datagram size".
Ping between tunnel source and tunnel dest with size 4096 and df
is ok, but all 1500-bytes packets are fragmented while encapsulating
into the gre tunnel.
6500/sup720.
In addition I use ipsec (with SPA-IPSEC-2G), but MTU is unchangable
for unprotected gre tunnels too. MTU on virtual GE to ipsec module
is 9216.
Big unfragmented packets from remote router (7200) are successfully
receiving and decrypting.

Any suggestions?

-- 
Pavel