Difference between loopback and dummy interfaces for use in Linux routing

[Maximilian Wilhelm]

Anno domini 2018 Wilhelm Schuster scripsit:

Hi,

> Can you give a scenario where I would want to use multiple dummy's
> instead of just adding/removing addresses to the loopback interface? I
> can't use a dummy interface for "real" packet processing since it just
> drops the packet. If the use case is to make addresses from
> loopback/dummy available on other interfaces, then does it matter if
> those addresses originally came from a single lo or multiple dummy's?

I use dummy interfaces for service IPs which are then distributed by
BGP inside my networks.

So I have three use cases:

 1. real loopback (lo): Loopback IP (v4+v6) where v4 == router-ID in OSPF

 2. dummy interface for local services ('srv') for services which are
    exclusivly run on this box.

 3. dummy interface for anycasted services ('anycast_srv') for
    services where on instance is running on this box.

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.

Best
Max
-- 
"Wer nicht mehr liebt und nicht mehr irrt, der lasse sich begraben."
 -- Johann Wolfgang von Goethe