On Fri, Jun 04, 2021 at 03:13:15PM +0100, Bob Briscoe wrote: > The L2TP RFC says sequencing /can/ be disabled for IP data, but it > doesn't say SHOULD or MUST. Is it possible that some operators enable > L2TP sequencing for IP data? And if so, do you know why they would? > Also, are you aware of any other types of tunnel that might try to keep > IP data packets in sequence?
How many intermediate headers are you considering between L2TP and where a carried IP header may exist? Maybe I'm getting the wrong end of the stick, but surely this engages the text from section 5.4 of RFC 2661: "For example, if the PPP session being tunneled is not utilizing any stateful compression or encryption protocols and is only carrying IP (as determined by the PPP NCPs that are established), then the LNS might decide to disable sequencing as IP is tolerant to datagram loss and reordering." This would then suggest if L2TP is carrying PPP, the PPP session is not multi-link, and is making use of compression (including one of the versions of IP header compression) in some form for IP packets, then reordering will impact the ability to decompress. So such an L2TP data session may well make use of sequence numbers to prevent reordering. I guess similarly in L2TPv3 when the PW is for PPP, and possibly also the fragmentation scheme in RFC 4623 which requires sequence numbers; and such PWE3 links could ultimately be carrying IP packets. DF (not an operator) _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
