On Oct 26, 2013, at 12:14 PM, Yaron Sheffer <[email protected]> wrote:
> > > On 2013-10-25 23:51, Yoav Nir wrote: >> >> On Oct 25, 2013, at 11:23 PM, Yaron Sheffer <[email protected]> wrote: >> >>>> >>>> Section 2.5.1 recommends using 1280-byte max IP datagram size for >>>> IPv6 (based on RFC 2460), and 576 bytes (based on RFC 1122). The big >>>> difference between those two RFCs is not some technical difference >>>> between IPv6 and IPv4, but that the former was written in 1998 while >>>> the latter is from 1989. By 1998 it was reasonable to mandate >>>> infrastructure that could handle 1280-byte datagrams. This has become >>>> more true, not less in the 15 years since RFC 2460. Pretty much all >>>> networks today can carry IPv6, and any network that can carry >>>> 1280-byte IPv6 packets, can just as well carry 1280-byte IPv4 >>>> packets. I don't think there's any point in still making this >>>> distinction today. >>>> >>>> >>> This draft is about broken networks/devices that are unable to handle IPv4 >>> fragments. Can we really assume that they can carry IPv6 traffic? >>> >>> Yes, RFC 1122 is very old, but if we recommend a larger size I would like >>> to see better justification. >> >> The original IKEv1 fragments were inspired by broken home routers that >> wouldn't keep enough state to NAT fragments. They still worked on Ethernet >> and 802.11 and had 1500-byte MTU. >> >> The current work was inspired by CGNs doing the same thing. They also deal >> with 1500-byte Ethernet. >> >> 1280 leaves room for various tunnels, encapsulations and what not. >> >> Of course, if your implementation is running in some constrained environment >> (like the Internet of Things on 802.15.4) you may need different MTUs. But >> on the open Internet? You just don't see PMTUs that small anymore. >> >> Yoav >> > If we give a recommendation, I think it should be based on measured data. See > for example Sec. 5.5 of > http://nlnetlabs.nl/downloads/publications/pmtu-black-holes-msc-thesis.pdf > Thanks for the link. And only 1 (out of >1150) probes found a PMTU in IPv4 smaller than 1280, and that was 1280. More than 2/3 were exactly 1500, and the vast majority was over 1400. Smallest they found was 1240. Any reason to set the limit (much) below that? Yoav _______________________________________________ IPsec mailing list [email protected] https://www.ietf.org/mailman/listinfo/ipsec
