V4 via V6 and IGP routing protocols

Sun Apr 3 19:02:03 UTC 2022

On 4/3/22 13:55, Dave Taht wrote:

> Periodically I still do some work on routing protocols. 12? years ago I had kind
> of given up on ospf and isis, and picked the babel protocol as an IGP
> for meshy networks because I felt link-state had gone as far as it
> could and somehow unifying BGP DV with an IGP that was also DV
> (distance vector) seemed like a path forward.

To scale the IGP, we only carry Loopbacks and interfaces (backbone 
infrastructure) in the IGP. Many operators have been doing this, for 
some time now, as a best pratice.

Customer routes as well as the DFZ is carried in iBGP.

The only issue we have hit with this design is hardware that ships with 
limited FIB (you're talking 4,000 slots or less). While this can be 
mitigated with things like 6PE and RFC 3107, there are, now, tons of 
hardware shipping without this physical restriction. For me, the 
simpler, the better.

> My question for this list is basically, has anyone noticed or fiddled
> with babel? It's supported
> in FRR, bird, and a very small standalone daemon.

Never heard of it as an IGP until now :-).

Googl'ing:

     https://en.wikipedia.org/wiki/Babel_(protocol)

> To recap that:
>
> "V4-via-v6 routing is a routing technique that allows routers with
> only IPv6 addresses (including link-locals) to forward IPv4 packets.
> It doesn't involve encapsulation (tunnelling), it doesn't involve
> translation (NAT), it just works.  For details, please see

Since around Junos 9 (2007), OSPFv3 shipped with the ability to carry 
IPv4 NLRI over an IPv6-only network. We never did implement that, as 
IS-IS integrated both protocols already. But it's been there for a while 
for OSPFv3.

I don't know when (or if) other vendors implemented the same thing for 
OSPFv3.

That said, nearly any OSPF house I'm aware of still runs both OSPFv2 and 
OSPFv3 side-by-side. I guess folk are probably unprepared to use OSPFv3 
for IPv4 NLRI.

Mark.