[RFC] Multicast and IPv6 Link Local Addresses

Toke Høiland-Jørgensen toke at toke.dk
Mon Apr 17 18:55:46 CEST 2017

Baptiste Jonglez <baptiste at bitsofnetworks.org> writes:

> Hi Jason,
> On Fri, Apr 07, 2017 at 04:02:49PM +0200, Jason A. Donenfeld wrote:
>> Various networking people have been poking and prodding about
>> supporting IPv6 Link Local addresses and about supporting special
>> but in case I do, I wanted to start spec'ing out what this might look
>> like in order to think about it better. There are a lot of odd
>> concerns to take into account, so I doubt that the below will wind up
>> as a final solution.
> This is good news!  I can't wait to see Babel running on a wireguard
> interface with several peers, or even what OSPF would look like on such a
> network.
> That being said, for the purpose of a routing protocol like Babel, I think
> it still makes more sense to use only *point-to-point* wireguard links.
> Link-local and multicast communication solves the problem of discovering
> remote routing daemon, but the AllowedIPs list is still static, which does
> not make sense for a routing protocol.  With point-to-point links, you can
> bypass this limitation by simply setting AllowedIPs to ::/0.  Of course,
> once we have dynamic AllowedIPs, this will change :)

Yeah, for the use case I'm envisioning, I would teach the routing daemon
to update wireguard's route tables...

> There is just the minor issue of subnets that encompass both unicast and
> multicast addresses, the simplest one being ::/0.  Such subnets could be
> automatically split by wireguard, or just have the "moving" semantic of
> unicast subnets.  With this last option, a user would have to explicitly
> add a subnet which is *within* a multicast prefix to trigger the "cloning"
> semantic.

I agree that the least confusing would be to only treat prefixes
entirely contained in the known multicast prefixes as having "cloning"


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