Another argument for public loopback/link addresses: merging networks. Fairly bad when you plan to merge two networks and loopback addresses are not unique anymore ;-) Regarding RIRs we haven't had real problems using public address space. As mentioned by Christopher: talk to them is the solution. Of course they will ask you if you can't use private address space - that's their job! Management in VPN networks: plan for address collisions. Anything else but (your own) public addresses can be used by the customers. 198.18.0.0/15 doesn't help you for all times ("oh, we use that for our extranet as all partners had 10.x.x.x in use like us"). Maybe using a separate management VRF on the CPE and DLCI/PVC/VLAN on the CPE-PE link is an option. Or use management address ranges in all 3 RFC1918 networks to lower the probability of collisions - often customers use only 1 or 2 address ranges. I've also seen NAT on the provider end of the management DLCI/PVC together with management address ranges per customer network. Regards, Marc On Friday, June 6, 2003, at 06:05 PM, m.rapoport@completel.fr wrote:

Hello, 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 services.

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 198.18.0.0/15 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 198.18.0.0/15 for this purpose ?

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

-- Marc Binderberger <marc@sniff.de> Powered by *BSD ;-)