Hi Pim, There were some changes around tap creation which likely caused the issue - https://github.com/FDio/vpp/commit/cb19c526dd1c907569a00936c35e8c1b663008dd#diff-f7f8eb1b374b1dd5000dcb44b237615f6bb8c5d29aa022a92356161f6bb96e60L1073. Prior to that, hw was being set to point to the tap interface.
When the CI verify jobs finish and give your gerrit the +1, I'll merge it. Thanks, -Matt On Thu, Mar 5, 2026 at 6:56 PM Pim van Pelt via lists.fd.io <pim= [email protected]> wrote: > Hoi folks, > > I was playing around with af-packet and creating LCP pairs with them. > I noticed a bunch of errors with 'l3 mac mismatch' while multicast > worked, unicast did not. > > I saw commits 1412d24ba and 3e00a101be but they are innocent, rolling > them back in my build would not fix the situation. > > I realized that linux-cp has a bug in lcp_interface.c: > - After tap_create_if() on L1064, hw still points to the PHY's HW > interface from L841. > - The STATUS_L3 flag ends up on the PHY (in my case the AF_PACKET > interface), not on tapXXXX. Linux sends unicast with the peer's real > MAC, which mismatches the tap's synthetic 02:fe:... mac address and thus > gets dropped. Multicast is allowed to bypass DMAC checks, and thus > multicast works. > > The fix seems simple - look up a new hw from the args.sw_if_index (the > TAP) and set the flag on that one. Considering how long we've had Linux > CP and no changes around the TAP creation that I could see, am I perhaps > misreading this? > > https://gerrit.fd.io/r/c/vpp/+/45103 is a fix. Without it, containerlab > created eth1/eth2/ethN af-packet interfaces, but the corresponding > tap4096/tap4097/tap4098 were not in promiscuous mode. With the gerrit, > containerlab works and the TAPs are in promiscuous mode. > > Please take a look. > > > > -- > Pim van Pelt <[email protected]> > PBVP1-RIPE https://ipng.ch/ > > > > >
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