[j-nsp] IPv6 MTU issue

[Alex]

My wild guess is that you are hitting a network of FreBSD/Olive/Linux IPv6 
routers with certain cards where when 802.1Q is enabled, MTU is 
automatically reduced by 4 bytes.
You can simulate it with Olive by enabling "vlan-tagging" on Intel PRO/100 
card.
My $0.02
Thanks
Alex


----- Original Message ----- 
From: "Gökhan Gümüs" <ggumus at gmail.com>
To: <juniper-nsp at puck.nether.net>
Sent: Friday, October 21, 2011 11:25 AM
Subject: [j-nsp] IPv6 MTU issue


> Dear all,
>
> I have an issue with IPv6 MTU.
>
> When i make a traceroute to one destination, the MTU size is reduced from
> 1500 to 1496, somehow...?
>
> What makes it worse is that hop which drops the MTU does not send ICMP
> "packet too long" message back..
>
> gg# scamper -I "trace -P udp -M abc
> traceroute from xxx to abc
> 1  s  0.192 ms [mtu: 1500]
> 2  d  0.356 ms [mtu: 1500]
> *3  f  1.422 ms [mtu: 1500]*
> *  4  g  1.107 ms [*mtu: 1496]*
> 5  h  1.145 ms [*mtu: 1496]
>
>
> On the link where MTU drops, output is as follows,
>
> Protocol inet, MTU: 1500
>
> Protocol inet6, MTU: 1500
>
>
>
> Software version is 10.0R4.7.
>
>
>
> Anybody has an experience on this behaviour before.
>
>
>
> Thanks and regards,
>
> Gokhan
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