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Re: Best Practices for Loopback addressing (Core routers & VPN CPE)
From: Marc Binderberger <marc () sniff de>
Date: Sun, 8 Jun 2003 14:27:47 +0200

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. 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:

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 ...

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

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