[Babel-users] v4-via-v6 and the IPv4 Dummy Address

[Toke Høiland-Jørgensen]

Juliusz Chroboczek <jch at irif.fr> writes:

> Hi,
>
> After I release v4-via-v6, I'll start working on merging HMAC and
> v4-via-v6 into babeld.  A v4-via-v6 router needs to be able to send ICMPv4
> packets even if it hasn't been allocated an IPv4 address; the simplest way
> to achieve that is to use the "IPv4 dummy address".
>
>   https://tools.ietf.org/html/draft-ietf-babel-v4viav6-03#section-3
>
> Question: how do we achieve this?  The best solution would be to modify
> the Linux kernel to use the dummy address for sending ICMPv4 when it has
> no IPv4 addresses available.  The second best would be to automatically
> add the IPv4 dummy address to the loopback interface when Babeld
> starts.

What does the kernel do currently? And will setting an address on the
loopback interface help at all? The documentation for the
icmp_errors_use_inbound_ifaddr sysctl[0] says this:

  Note that if no primary address exists for the interface selected,
  then the primary address of the first non-loopback interface that has
  one will be used regardless of this setting.

-Toke

[0] In https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html