Hi, There is a proposal to use TCP MSS clamping to deal with MTU issues that comes from Dual-stack lite's tunnel encapsulation.
I think it would be good if TCPM could provide some feedback on this proposal. The relevant document and section: http://tools.ietf.org/html/draft-ietf-softwire-dual-stack-lite-00 7.4. MTU Using an encapsulation (IP in IP or L2TP) to carry IPv4 traffic over IPv6 will reduce the effective MTU of the datagrams. Unfortunately, path MTU discovery is not a reliable method to deal with this. As such a combination of solutions is suggested: o For TCP traffic, let the carrier-grade NAT rewrite the MSS in the first SYN packet to a lower value. o For non-TCP traffic, perform fragmentation and reassembly over the tunnel between the home gateway and the carrier grade NAT. In practice, this means put the IPv4 packet into a large IPv6 packet and fragment/reassemble the IPv6 packet at each endpoint of the tunnel. There is a performance price to pay for this. Fragmentation is not very expensive, but reassembly can be, especially on the carrier-grade NAT that would have to keep track of a lot of flows. However, such a carrier-grade NAT would only have to perform reassembly for large UDP packets sourced by customers, not for large UDP packets received by customers. In other words, streaming video to a customer would not have a significant impact on the performance of the carrier-grade NAT, but will require more work on the home gateway side. Cheers Magnus Westerlund IETF Transport Area Director & TSVWG Chair ---------------------------------------------------------------------- Multimedia Technologies, Ericsson Research EAB/TVM ---------------------------------------------------------------------- Ericsson AB | Phone +46 10 7148287 Färögatan 6 | Mobile +46 73 0949079 SE-164 80 Stockholm, Sweden| mailto: [email protected] ---------------------------------------------------------------------- _______________________________________________ Softwires mailing list [email protected] https://www.ietf.org/mailman/listinfo/softwires
