Lectures notes for 2010 - KTH

3 When retransmitting to a remote address for which the IP datagram
appears too large for the path MTU to that address, the IP datagram
should be retransmitted without the DF bit set, enabling it to be
fragmented. While initial transmissions of IP datagrams must have
DF set.
4 Sender maintains an association PMTU (= smallest PMTU discovered
for all of the peer’s destination addresses); when fragmenting
messages this association PMTU is used to calculate the size of each
fragment ⇒ retransmissions can sent to an alternate address without
encountering IP fragmentation
Maguire Path MTU Discovery 6: 36 of 44
maguire@kth.se 2010.03.21 Internetworking/Internetteknik