Silence on the Wire

Reliability or Performance: The DF Bit Controversy

Path MTU discovery (PMTUD) is a fingerprinting venue that is closely related to the IP fragmentation avoidance scheme described in Chapter 9.

Recent versions of the Linux kernel (2.2, 2.4, 2.6) and of Windows (2000 and XP) implement and enable PMTUD by default. Thus, unless this setting is changed, all traffic originating from them has a don’t fragment (DF) bit set. Again, the path discovery algorithm tends to cause issues in some rare but not entirely unheard of situations.

Path MTU Discovery Failure Scenarios

The problem with PMTUD is that it depends on the ability for the sender of a packet to receive the ICMP error message “fragmentation required but DF set” and to determine the optimal settings ...