Unable to set IP6_TNL_F_IGN_ENCAP_LIMIT on ip6tnl

[spike77453]

Hi,

I'm trying to set up an ip6tnl interface (mode ipip6) with the IP6_TNL_F_IGN_ENCAP_LIMIT flag set. With ip link this can be done by running

ip link add mytunnel type ip6tnl mode ipip6 local <local_addr> remote <remote_addr> encaplimit none

(see https://github.com/iproute2/iproute2/blob/68eef949c29e02261063de641762e37fda7193d3/ip/link_ip6tnl.c#L193-L195)

When running the following snippet (ip6tnl_encap_limit='none' is obviously not a valid option):

    ipr = IPRoute()
    ipr.link('add',
        ifname='mytunnel',
        kind='ip6tnl',
        ip6tnl_local=ip6tnl_local,
        ip6tnl_remote=aftr_address,
        ip6tnl_encap_flags=0x1,
        ip6tnl_ttl=64,
        ip6tnl_proto=4
    )
    ipr.link('set', ifname='mytunnel', state='up')

the outgoing traffic still has a tunnel encapsulation limit set. The IPv6 headers look like this:

• When doing ip link add ...:

  60 0d 19 00 00 54 04 40 src dest
  

• When running the snippet mentioned above (notice the next header field 04 vs. 3c plus 8 extra payload bytes):

  60 09 47 32 00 5c 3c 40 src dest 04 00 04 01 04 01 01 00
  

This is due to the tunnel being created with encaplimit 0 instead of encaplimit none:

# ip -6 tunnel
mytunnel: ip/ipv6 remote <remote_addr> local <local_addr> encaplimit 0 hoplimit 64 tclass 0x00 flowlabel 0x00000 (flowinfo 0x00000000)

vs.

# ip -6 tunnel
mytunnel: ip/ipv6 remote <remote_addr> local <local_addr> encaplimit none hoplimit 64 tclass 0x00 flowlabel 0x00000 (flowinfo 0x00000000)

The IP6_TNL_F_IGN_ENCAP_LIMIT flag is defined here: ip6_tunnel.h#L13
ip6tnl_proto=4 is ipip6, see link_ip6tnl.c#L161-L165 and in.h#L36-L37

[svinota]

Thanks for the detailed report, investigating