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Re: Best Practices for Loopback addressing (Core routers & VPN CPE)
From: "Christopher B. Zydel" <chris () cv net>
Date: Fri, 06 Jun 2003 18:58:15 -0400

In situations like this, I find it helpful to provision an additional loopback interface for each peer that has more than one connection to the same router. This lets us remain in control of our own destiny rather than relying on outside parties to do reconfiguration when circuits need to get moved between routers.

I wouldn't agree with the original poster's statement that using address space obtained from one of the public registries for internal purposes will be an issue. ARIN, et al shouldn't have a problem with using address space obtained from them for internal uses (i.e. not announced to the public internet) If you have concerns about how they might react to this, I'd suggest engaging them directly for advice on how to structure your request. In my past experience, I've found it easier to discuss my request with ARIN prior to submitting it, just to be sure they understand what I'm intending to do, and that I'm giving them all of the necessary data. The last thing you want to do is have that dialogue once they're already reviewing your request, it's likely to make the process take far longer than necessary.

FWIW, I am loathe to use address space that is not publically routable for anything I can't rip apart and renumber inside of a few hours. There are a many ways to give yourself a headache that are far more enjoyable. :-)


Daniel Golding wrote:

Consider the situation where you have a peer or customer who needs to do
ebgp multihop peering from loopback to loopback. This happens
infrequently, but it does happen. You need public IP address space to
(reasonably) make this work. I know you are assuming this won't happen,
but the day you need to provision two OC-12s to the same provider or peer,
and want to load balance them effectively...


On Fri, 6 Jun 2003 m.rapoport () completel fr wrote:

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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