Best Practices for Loopback addressing (Core routers & VPN CPE)

m.rapoport at m.rapoport at
Fri Jun 6 16:05:10 UTC 2003

I was wondering what are the choices made by Service Providers on the
loopback addressing.
The context is an IP/MPLS Backbone providing both Internet and BGP-VPN

 I have 2 different cases to address :

1)  Loopbacks on the backbone routers :
I have the feeling that general practice is to use public IP adresses for
Core routers.

However, considering that these loopbacks are only used for routing
protocols (OSPF,BGP, LDP)
and for network management (SNMP, telnet, ...) and that  these addresses
don't need to visible from public Internet
(not seen in traceroute, not seen on Internet BGP announces ...) I am
considering to
use private  RFC1918 for a new Backbone deployment.

N.B. : Assumption is that e-BGP sessions with Internet peers are done on
public interface IP, not on loopback IP.

Is there some specific case I am missing where public loopback IP is
required, and therefore
private adressing would break something (maybe some Carrier-to-Carrier
scenario ?) .

I also plan to use RFC1918 addresses for Internet CPE routers loopbacks.

2) Loopback on CPE routers of the MPLS VPN customers.
For this case, the issue is to assign the adresses in a global range for
all the CPE of
all the VPN customers.
In fact, all these loopback will need to be part of the Network Management
VPN for supervision needs.
Using RFC 1918 addresses might create trouble as there is a very high
chance that the VPN customers
are already using 1918 addresses, this might generate addresses conflicts.
Addresses unicity among all the customers is required due to the  Network
Management VPN common
to all the customers.
Using public address guarantee unicity, but will create issues with public
registries, considering that
 these addresses are used for internal needs.
I am considering to use the defined in RFC 2544 and listed in
RFC 3330 as reserved for
lab testing.
I suppose that no VPN customer uses this prefix for its internal IP
addressing, and as these addresses don't
need to be announced on Internet.
Do you suggest to use an other prefix than for this purpose ?

If you consider your adressing policy as  touchy topic in terms of
security, don't hesitate to reply in private ...

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