Re: Using RFC1918 on Global table as Loopbacks

[Randy Bush <randy () psg com>]

> I have recently encountered some operational differences at my new
> organization that are not what I have been exposed to before, where
> the loopback of the core network devices is being set from RFC1918
> while on the global routing table. I'm sure this is not a major issue
> but I have mostly seen that ISPs use global IPs for loopbacks on
> devices that would and hold global routing.
>
> My question is, what is the most used or recommended way to do this,
> if I continue to use RFC1918 I will save some very much desired public
> address space, but would this come back to bite me in the future?

loopback addressing does not have to be used for router ids.  so
decouple that consideraton.  make up router ids; 1, 42, 3, 4, ...
whatever.  they just need to be unique within the AS.

< corner case >

you may want to have your loopbacks in real global space for routers
which are on an IX.  i have been having fun where an IX router is
sourcing packets from the IX interface, and responses can not come
back because the IX space is not announced globally.  so one wants
to tell the protocol originating those packets (ntp, dns, whatever)
to source from the loopback.  and, for replies to get back to that
loopback, it needs to be in real global space.

randy