On 2019/01/11 22:13, Fredrik Gustavsson wrote: > Den fre 11 jan. 2019 kl 05:23 skrev Toshiaki Makita > <makita.toshi...@lab.ntt.co.jp>: >> >> On 2019/01/10 22:26, Fredrik Gustavsson wrote: >>> commit affede4a779420bd8510ab937251a3796d3228df >>> Author: Fredrik Gustavsson <gustf...@gmail.com> >>> Date: Tue Jan 8 11:21:39 2019 +0100 >>> >>> veth: Do not drop packets larger then the mtu set on the receiving side >>> >>> Currently veth drops all packets larger then the mtu set on the receiving >>> end of the pair. This is inconsistent with most hardware ethernet drivers >>> that happily receives packets up the the ethernet MTU independent of the >>> configured MTU. >>> >>> There should not be a need for dropping IP packets at receiver with >>> size > configured IP MTU, IP MTU is for fragmentation at sender side. >>> And IP packets with size > receiver L2 MTU will be dropped at sub-IP layer. >> >> But with current veth behavior setting MTU effectively sets MRU as well. >> This may be being used to drop unexpectedly long packets e.g. from >> containers on container host. If we unconditionally change this behavior >> it can cause regression on some environment. This should be an option at >> least. >> >> BTW there was a similar precedent attempt. You might want to take a look. >> >> https://www.mail-archive.com/netdev@vger.kernel.org/msg167636.html >> https://www.mail-archive.com/netdev@vger.kernel.org/msg167899.html >> > Good argument, but do you agree that it shouldn't be working like it > does?
Not sure. As discussed in the previous thread I think some hardware can limit MRU < 1500 by configuring MTU, so to me it is not especially odd. > But not sure if such a case would exist but breaking > compatitbility have been discussed in other threads. So your saying > that people have actually used it as a receiving limit for IP packets? No, I'm saying it can be used in that way. Even though we did not confirm if there really are people using features in a certain way, we usually assume there are, as long as the usage is possible, because so many people use Linux. -- Toshiaki Makita
