[PVE-User] Frame errors in IPv6-in-IPv4 tunnel interface (!)

[Mario Galindez]

Folks,

I have a LIX container running in Proxmox 4.4-24.   My container is:

Linux mybox 4.4.134-1-pve #1 SMP PVE 4.4.134-112 (Thu, 05 Jul 2018 12:39:16
+0000) i686 athlon i686 GNU/Linux.

This container has multiple IPv6-in-IPv4 tunnels.   Some of them work okay.
But there is one that doesn't.   After debugging the problem, it turns out
that packets received on the tunnel interface are marked as having "frame
errors", and therefore the packets are blackholed:

ipv6-tun: flags=209<UP,POINTOPOINT,RUNNING,NOARP> mtu 1480
inet6 2001:470:aaaf:201::1111 prefixlen 128 scopeid 0x0<global>
inet6 fe80::4cef:6524 prefixlen 64 scopeid 0x20<link>
sit txqueuelen 1 (IPv6-in-IPv4)
RX packets 0 bytes 0 (0.0 B)
RX errors 503 dropped 0 overruns 0 frame 503
TX packets 921 bytes 99339 (99.3 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

Curiously enough, if I run tcpdump on the virtual ethernet card (as opposed
to the tunnel interface), I can see the IPv6-in-IPv4 packets, with valid
checksums, etc.

Any clues regarding what might be going on, and how to solve the problem?

thanks,
- m