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Changed 6to4 tunnel server, getting checksum errors on SIT tunnel

Started by lucaberta, April 14, 2020, 10:30:30 AM

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Hello everyone,

I have been successfully running an HE 6to4 tunnel using a Debian distribution on an old Geode-based small form PC.

I have now updated the server to a Raspberry Pi 2 running ArchLinux32. I have reused pretty much the same exact configuration I had on the old server.

For some yet unknown reason, I cannot seem to make the HE tunnel work, and what I found out is that there are checksum errors in every packet sent on the tunnel, as displayed by tcpdump.

This is what I have on the tunnel interface:

he-ipv6: flags=209<UP,POINTOPOINT,RUNNING,NOARP>  mtu 1480
        inet6 2001:xxx:xx:xxx::2  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::4f28:xxxx  prefixlen 64  scopeid 0x20<link>
        sit  txqueuelen 1000  (IPv6-in-IPv4)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 4  dropped 0 overruns 0  carrier 4  collisions 0

See those TX errors, which are marked as "carrier" errors? This is just after a reboot.

Locally on the machine, the IPv6 tunnel side pings fine, but no packets to the IPv6 internet make it thru the tunnel, and the error counter increases. IPv6 routes are OK.

The HE tunnel broker IPv6 endpoint from the IPv6 internet pings well.

Does anyone have any idea what might cause checksum errors on the SIT tunnel? The kernel is a new 4.19.114 build under ArchLinux32.

I have tried fiddling with a few sysctl parameters related to forwarding, hoping that it was an IPv6 routing issue, but it did not solve the issue at all.

Any hints on how to further troubleshoot, or on what might be the cause of these checksum errors?