mtu mis-match

Thu Mar 20 09:29:19 UTC 2008

On Mar 19, 2008, at 8:05 PM, ann kok wrote:

>
> Hi
>
> I have this problem about mtu mismatch
>
> Some DSL clients, some are working fine.
> (browsing...ping ...)
>
> Some DSL clients have this problem
> they can't browse the sites.
> they can ssh the host but couldn't run the command in
> the shell prompt
> ping packet are working fine (no packet lost)
>
> Why?
> but I still don't know why mtu can cause this problem
>
> Thank you for your help

Sounds like the old PPPoE issue : 1500 vs 1492.
It usually is dealt with on a per destination basis:

For a given destination (the ones that are causing problems to you)  
start with :
ping -D -s 1500 <your_destination> and lower the -s value until the  
ping goes through.
-D forces "don't fragment bit"
-s manages packetsize

When your ping reaches your destination, your -s size is good (for  
that destination only...).

Greg VILLAIN
Independent Network & Telco Architecture Consultant

Greg VILLAIN
Independant Network & Telco Architecture Consultant
+33 6 87 48 66 14