New: ipip6 MTU cannot be set lower than 1280

Bugme-new Andrew Morton 1 participant 1 message Mar 19, 2010 1 message not in the archive

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Andrew Morton

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2010-03-19 21:20 UTC #1 lore raw

(switched to email. Please respond via emailed reply-to-all, not via the bugzilla web interface).

Quoted 35 lines · On Sat, 13 Mar 2010 14:38:54 GMT [email protected] wrote:

http://bugzilla.kernel.org/show_bug.cgi?id=15530
           Summary: ipip6 MTU cannot be set lower than 1280
           Product: Networking
           Version: 2.5
    Kernel Version: 2.6.32
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: low
          Priority: P1
         Component: IPV6
        AssignedTo: [email protected]
        ReportedBy: [email protected]
        Regression: No
The (inner) MTU of a ipip6 (IPv4-in-IPv6) tunnel cannot be set below 1280, which is the minimum MTU in IPv6. However, there should be no IPv6 on the tunnel interface at all (ipip6 cannot transport it), so the IPv6 rules should not apply.
root@pest:~# ip -6 tunnel add test1 mode ipip6 remote 2001:xxxx::26 local
2001:xxx::1:1
root@pest:~# ip link set test1 mtu 1280
root@pest:~# ip link set test1 mtu 1279
RTNETLINK answers: Invalid argument
This prevents the tunnel from work on paths that only support a (outer) IPv6 MTU of 1280, since the tunnel adds an additional overhead of 40 bytes.
Setting net.ipv6.conf.<if>.disable_ipv6=1 and/or removing the IPv6 link-local address on the tunnel interface does not help.