SamDobs Pursuit of Happyness through Techyness....

In this Post I will show you How to Set DF bit on a Windows Machine (Windows 7).

Below is the PING options output:

H:\>ping

Usage: ping [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS]
            [-r count] [-s count] [[-j host-list] | [-k host-list]]
            [-w timeout] [-R] [-S srcaddr] [-4] [-6] target_name

Options:
    -t             Ping the specified host until stopped.
                   To see statistics and continue - type Control-Break;
                   To stop - type Control-C.
    -a             Resolve addresses to hostnames.
    -n count       Number of echo requests to send.
    -l size        Send buffer size.
    -f             Set Don't Fragment flag in packet (IPv4-only).
    -i TTL         Time To Live.
    -v TOS         Type Of Service (IPv4-only. This setting has been deprecated
                   and has no effect on the type of service field in the IP Head
er).
    -r count       Record route for count hops (IPv4-only).
    -s count       Timestamp for count hops (IPv4-only).
    -j host-list   Loose source route along host-list (IPv4-only).
    -k host-list   Strict source route along host-list (IPv4-only).
    -w timeout     Timeout in milliseconds to wait for each reply.
    -R             Use routing header to test reverse route also (IPv6-only).
    -S srcaddr     Source address to use.
    -4             Force using IPv4.
    -6             Force using IPv6.


Now let's do a Ping test to Yahoo with MTU Size 1470 with DF Bit set.

H:\>ping yahoo.com -f -l 1470

Pinging yahoo.com [98.138.253.109] with 1470 bytes of data:
Reply from 98.138.253.109: bytes=1470 time=352ms TTL=39
Reply from 98.138.253.109: bytes=1470 time=442ms TTL=39

Ok, that's working so now let's do another test with 1500.

H:\>ping yahoo.com -f -l 1500

Pinging yahoo.com [98.138.253.109] with 1500 bytes of data:
Reply from 135.75.222.106: Packet needs to be fragmented but DF set.
Reply from 135.75.222.106: Packet needs to be fragmented but DF set.
Reply from 135.75.222.106: Packet needs to be fragmented but DF set.
Reply from 135.75.222.106: Packet needs to be fragmented but DF set.

HTH...

Sam