[Babel-users] Merging v4-via-v6: need advice

[Toke Høiland-Jørgensen]

Juliusz Chroboczek <jch at irif.fr> writes:

> Hi,
>
> I'm in the process of merging v4-via-v6 into mainline babeld, and I need
> some advice about the default configuration.
>
> V4-via-v6, is described here:
>
>   https://datatracker.ietf.org/doc/html/draft-ietf-babel-v4viav6
>
> It's a technique that allows an IPv6-only router to forward IPv4 packets,
> which makes it easier to administer a double-stack network, since only
> IPv6 addresses need to be allocated inside the network.  However,
> a v4-via-v6 router needs to be able to originate ICMPv4 packets, and these
> packets need to have a source address.
>
> I haven't done extensive testing yet, but my preliminary investigations
> indicate that the Linux kernel behaves as follows:
>
>   - if the router has an IPv4 address on at least one interface, the
>     address is borrowed as the source of the ICMPv4 packet;
>   - if the router has no IPv4 address at all, no ICMPv4 packet is sent,
>     which may cause blackholes.
>
> The issue is describes in Section 3 of the draft, which suggests using the
> IPv4 dummy address 192.0.0.8 when no IPv4 address is available.  Using the
> dummy address will require some minor surgery to the Linux kernel, and
> I haven't implemented it yet.  So while we wait for somebody (me or
> someone else) to implement support for the dummy address, what should
> babeld's default behaviour be?
>
> 1. Disable v4-via-v6 by default, and assume that an administrator who
>    enables it knows what they're doing?
> 2. Check for IPv4 addresses, and enable v4-via-v6 automatically if there
>    is at least one IPv4 address?
> 3. 3=1+2, behave like (2), but allow overriding the daemon's decision?
>
> Any better ideas?

Not really - 3 would be my preference of the above, I think. Do the
right thing by default, but don't second-guess the user if they
explicitly ask for a particular behaviour... :)

-Toke