On Thu, May 30, 2019 at 2:08 AM Steinar H. Gunderson <steinar+ker...@gunderson.no> wrote: > > Hi, > > I'm trying to connect some VMs over EoGRE (using gretap on my side): > > ip link add foo type gretap remote <remote> local <local> > > This works fine for large packets, but the system in the other end > drops smaller packets, such as ARP requests and small ICMP pings.
Is the other end Linux too? > > After looking at the GRE packets in Wireshark, it turns out the Ethernet > packets within the EoGRE packet is undersized (under 60 bytes), and Linux > doesn't pad them. I haven't found anything in RFC 7637 that says anything > about padding, so I would assume it should conform to the usual Ethernet > padding rules, ie., pad to at least ETH_ZLEN. However, nothing in Linux' IP > stack seems to actually do this, which means that when the packet is > decapsulated in the other end and put on the (potentially virtual) wire, > it gets dropped. The other system properly pads its small frames when sending > them. If the packet doesn't go through any real wire, it could still be accepted by Linux even when it is smaller than ETH_ZLEN, I think. Some hardware switches pad for ETH_ZLEN when it goes through a real wire. So, how is your packet routed between different VM? Via a Linux bridge? > > Is there a way to get around this, short of looping the packets out through a > physical wire to get the padding? Is it simply a bug? I've been testing with > 4.19.28, but it doesn't look like git master has any changes in this area. > It is still too early to say it is a bug. Is this a regression? Thanks.
