Question on path mtu and IP fragmentation in Linux kernel 3.0

[Sudharsan Vijayaraghavan]

Hi,

i find that even when /proc/sys/net/ipv4/ip_no_pmtu_disc is 0 (default
value), that
is path mtu is enabled, IP layer fragments the packets if it exceeds MTU

For example MTU is 1500, i do ping -s 15000 <ip addr>, IP layer nicely fragments
the packets, how is that possible?

Does that mean PATH MTU is excercised earlier for that route and lowest MTU is
already negotiated for the destination IP address, thats dst_mtu is
already calculated

Please give expert comments

Thanks,
Sudharsna