[c-nsp] Ping test with DF bit and MTU / IP MTU value

[Pshem Kowalczyk]

Hi,

On 19 January 2011 15:20, Muhammad Atif Jauhar <atif.jauhar at gmail.com> wrote:
> Hi,
>
> I am testing the link and face issue.
>                  1. while performing ping test without df bit, I am able to
> ping with size upto 18024
>                  2. while performing ping test with df bit, I am able to
> ping with size 1520
>                  3. while performing ping test with df bit, I am able to
> ping with size more than 1520
>
> *Kindly let me know, why I am not able to ping with DF bit with size more
> than 1520 (MTU value). How can I troubleshoot the issue. *

Points 2 and 3 seem to be contradictory. Assuming that you actually
meant that you can not ping with packets bigger then 1520 with the DF
bit set - this is expected behaviour. The DF bit tells the routers
that they can not fragment that packet (which they do if the DF is not
set). As your MTU is 1520 the biggest packet with DF bit set can only
be 1520. Anything bigger won't be forwarded.

kind regards
Pshem