Difference between loopback and dummy interfaces for use in Linux routing

[Maximilian Wilhelm]

Anno domini 2018 Wilhelm Schuster scripsit:

> On 2018-04-27 21:47, Maximilian Wilhelm wrote:
> > This way it's easy to have different direct protocols in bird and
> > easily tag, filter and/or announce prefixes within your network
> > accordingly. real loopback IPs are part of the IGP (OSPF), both 2 and
> > 3 are read by instances of protocol direct and distributed by (i)BGP.

> I didn't consider that, but it looks like an interesting approach.
> Reading the bird documentation, it slightly discourages from using the
> direct protocol:

> > The question is whether it is a good idea to have such device routes
> > in BIRD routing table. OS kernel usually handles device routes for
> > directly connected networks by itself so we don't need (and don't want)
> > to export these routes to the kernel protocol.

That's true. And bird does not export devices routes back into the
kernel if you don't force it to. So that's a non-issue.

> > OSPF protocol creates device routes for its interfaces itself

Also true. But if you want to run a SP like backone, you don't want to
carry routes for services within the IGP. If OSPF is ok for you,
making the lo/dummy interface a stub interface will get you a similar
effect and you are done.

> > and BGP protocol is usually used for exporting aggregate routes.

The keyword here is 'usually'. If we are talking about eBGP between
different organisations, this will mostly be the case. If we are
talking about iBGP within your network, BGP can carry quite a lot of
/32 and/or /128 routes for (anycasted) services.

> > But the Direct protocol is necessary for
> > distance-vector protocols like RIP or Babel to announce local networks.

That's an entire different story :)

Best
Max
-- 
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