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" <[email protected]>
To: <[email protected]>
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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