Using RFC1918 on Global table as Loopbacks

Thu Oct 5 17:42:22 UTC 2023

* GutierrezJ at westmancom.com (Javier Gutierrez) [Thu 05 Oct 2023, 19:25 CEST]:
>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?

The recommendation is to make Router-IDs globally unique. They're used 
in collision detection. What if you and a peer pick the same non 
globally unique address? Any session will never come up.

You need globally unique IP addresses on routers anyway, to send ICMP 
error packets from.

	-- Niels.