Ole, thanks so much for your warm help. > The next steps for tunnels, to help avoid fragmentation is to add some sort of > tunnel path MTU discovery.
It looks very interesting and helpful. And I'm looking forward to seeing it. However, we fail to send big packet greater than MTU now, for example, We have MTU = 1500, when 1500bytes packets are encapped by vxlan protocol, of course, the size of packets is bigger than MTU at the time , it looks that sending packets fails now. BTW Is DPDK IP fragment/reassembly supported in VPP now? Thanks Zhiyong > -----Original Message----- > From: vpp-dev@lists.fd.io [mailto:vpp-dev@lists.fd.io] On Behalf Of Ole Troan > Sent: Wednesday, September 26, 2018 7:06 PM > To: Yang, Zhiyong <zhiyong.y...@intel.com> > Cc: vpp-dev@lists.fd.io; Kinsella, Ray <ray.kinse...@intel.com> > Subject: Re: [vpp-dev] one question about IP fragment > > Zhiyong, > > > When I use vxlan in both VM and physical machine , packet > > drop issue > is come across, after setting VPP MTU = 1600, this issue will disappear. As > we > all know, some of routes on the network doesn’t support more than 1518 bytes > packet. > > Should I try to use IP fragment in this case? Or any other better solution? > Does VPP IP fragment work now? If yes, Could you show me how to configure? > Thank you very much. > > Fragmentation now works. Currently both for IPv4 and IPv6 packets are > fragmented in ip{4,6}_rewrite. Note that only locally originated IPv6 packets > can > be fragmented, and only IPv4 packets with DF = 0. > Assuming the above two restrictions are adhered to, if the VXLAN node sent > packets larger than the outgoing interface MTU they should be fragmented now. > There is no configuration for fragmentation. (Although I am thinking of > adding a > knob, with default disabled). > > For reassembly, VPP has a short-coming, It can only reassemble as an input > feature, meaning all fragments, even though not destined for the VPP instance > itself are reassembled. > I think Juraj is working on a fix for that. > > The next steps for tunnels, to help avoid fragmentation is to add some sort of > tunnel path MTU discovery. > > But in short, you are much better off with a well managed MTU, than you are > with fragmentation. > See our draft in intarea for a list: > https://tools.ietf.org/html/draft-ietf-intarea- > frag-fragile-00 > > Cheers, > Ole
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