Strange MTU-ish problem

Timothy Murphy gayleard at eircom.net
Tue Jan 6 11:03:29 UTC 2009


Paul Flo Williams wrote:

>> [tim at mary tmp]$ ping -s 1466 -c 3 -M do www.google.com
>> PING www.l.google.com (74.125.39.104) 1466(1494) bytes of data.
>> From homegate.homenet.telecomitalia.it (192.168.1.1) icmp_seq=1 Frag
>> needed and DF set (mtu = 1492)
>> 
>> Incidentally, what exactly does "DF set" mean?
>> Is it telling me that DF is set,
>> or that it should be set (or even, should not be set)?
>> If the latter, how can I do that?
> 
> DF is the Don't Fragment bit in the IP header flags field. It's telling
> you that you set it (with -M do), so it can't fragment the packet.

But I get the DF set response even if I don't use the -M option:
----------------------------------------------------------
[tim at mary etc]$ ping -s 1466 www.google.com
PING www.l.google.com (74.125.39.99) 1466(1494) bytes of data.
>From homegate.homenet.telecomitalia.it (192.168.1.1) icmp_seq=1 Frag needed and DF set (mtu = 1492)
^C
----------------------------------------------------------

Nb I have solved the problem, as I mention elsewhere in the thread.







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