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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