Cisco Systems: Resolve IP Fragmentation, MTU, MSS, and PMTUD Issues with GRE and IPSEC

Resolve IP Fragmentation, MTU, MSS, and PMTUD Issues with GRE and IPSEC - Cisco Systems The purpose of this document is to present how IP Fragmentation and Path Maximum Transmission Unit Discovery (PMTUD) work and to discuss some scenarios involving the behavior of PMTUD when combined with different combinations of IP tunnels. The current widespread use of IP tunnels in the Internet has brought the problems involving IP Fragmentation and PMTUD to the forefront.