[PLUG] Cannot set mtu in profile.d on Ubuntu 8.10

Kaustubh Gadkari kaustubh.gadkari at gmail.com
Tue Apr 13 00:23:06 PDT 2010


On Tue, Apr 13, 2010 at 1:09 AM, Abhijit Bhopatkar
<bain at devslashzero.com> wrote:
>> 1. Even though I understand that the VPN server adds headers and hence the
>> need to lower the MTU, I cannot understand why communication stalls when I
>> talk to CVS in such a situation, and it does not stall with regular internet
>> traffic.
>
> The cvs will have a huge bulk traffic going in and out. The main
> problem with MTU is not at server or client side, but is usually in
> the middle, the routers. The problem is that some routers on the
> network are not able to handle large packets very well. They start
> building up huge chains of backlog packets and eventually cause TCP
> retransmissions.

Usually, routers will drop packets that they cannot handle on the fast
path (on the line cards' switching fabric). This causes TCP to
timeout, causing retransmissions.

That apart, I would guess that since only the CVS traffic is affected,
there is something wrong/badly configured at the router/server at the
CVS end. A MTU of 1200 (which solves the problem, as Parag stated) is
ridiculously low.

Kaustubh

-- 
Kaustubh Gadkari
kaustubh [dot] gadkari [at] gmail [dot] com



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