There is no option to set the DF bit in the regular PING tool in Linux/Debian, there are two alternatives. One is to use the HPING tool and the second good tool TRACEPATH.
Download the Debian package:
iputils-tracepath – Tools to trace the network path to a remote host
After the installation just run tracepath <destination> and the tool will provide path MTU discovery, here is an example:
debian@july:~# tracepath cisco.com
1: july.interhost.co.il (84.95.244.160) 0.204ms pmtu 1500
1: 84-95-244-2.reserved.interhost.co.il (84.95.244.2) 0.515ms
2: 80.179.229.1.static.012.net.il (80.179.229.1) 18.426ms
3: pt-212.199.73.69.static.012.net.il (212.199.73.69) 0.597ms
4: pos3-0.ar03.ldn01.pccwbtn.net (63.218.13.65) 74.534ms
5: 63.218.94.186 asymm 9 160.245ms
6: 63.218.94.186 asymm 9 159.253ms
7: ded4-g8-3-0.sntc01.pbi.net (151.164.41.165) asymm 11 227.422ms
8: 64.161.0.62 asymm 16 214.835ms
9: sjc5-dmzbb-gw1.cisco.com (128.107.224.105) asymm 15 214.120ms
10: sjce-dmzbb-gw1.cisco.com (128.107.224.2) asymm 15 212.825ms
11: sjck-dmzdc-gw1-gig1-1.cisco.com asymm 15 212.723ms
It will also finds asymmetric routes which is very useful too.