Strange MTU-ish problem

[Paul Flo Williams]

Timothy Murphy 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.