Hi, Ole, > On Aug 8, 2025, at 12:26 AM, Ole Troan <otr...@employees.org> wrote: > >> Additionally: >> >>> On Aug 7, 2025, at 1:15 PM, Templin (US), Fred L >>> <Fred.L.Templin=40boeing....@dmarc.ietf.org> wrote: >>> >>> Many tunneling protocols live by “grace” and assume 1500 everywhere. But, >>> robust >>> tunneling protocols need to live by the “law”, and the law says 1280. >> >> And its subtle - for IPv4, they assume 1500 everywhere but it’s really 576 >> after reassembly at the receiver. >> >> For IPv6, it’s 1280 over each hop BUT up to 1500 after reassembly at each >> receiver. >> >> These and other aspects are why this isn’t just an op-ed. > > I think the current text is fine from a historical perspective. > For future recommendations I would prefer a recommendation that tunnels must > support link-layer segmentation and reassembly. > That could be UDP options FRAG or something else. > > Outer IP fragmentation is undesirable for multiple reasons. > E.g. a tunnel tail-end has to reassemble _before_ it can check if the > fragment chain belongs to a tunnel. Last I looked, a lot of IP fragments are > part of attacks, and they are costly to process. > > Ole
Tunnel fragments must be reassembled by the receiver - that’s a fundamental point of the document. The mechanism used for fragmentation and reassembly happens on the packet being tunneled, not within that packet. That is what outer fragmentation refers to - not necessarily fragmentation at the outermost IP layer. I.e., yes, we can avoid use of IP fragmentation IF there are other protocol layers available as part of tunnel encapsulation. But regardless of method used, the tunnel endpoint MUST do the reassembly. That clarification can be added. Joe _______________________________________________ Int-area mailing list -- int-area@ietf.org To unsubscribe send an email to int-area-le...@ietf.org
