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Re: Best Practices for Loopback addressing (Core routers & VPN CPE)
From: Danny McPherson <danny () tcb net>
Date: Fri, 06 Jun 2003 11:19:46 -0600


On 6/6/03 10:05 AM, "m.rapoport () completel fr" <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
services.

If the BGP Identifier, which is used for connection collision resolution and
path selection (among others seemingly random things) conflicts you'll have
issues.  

In my experience even mediocre IP addressing frameworks typically don't have
issues with RIRs when space is appropriately justified (i.e., there
typically aren't issues with loopback and inter-router address space
justification).

What I'd be more concerned with is loopback IP allocation and it's effect on
aggregation, stability, and other network policies (e.g., source-interface
type stuff).  For example, using a single contiguous block for all loopback
IPs significantly simplifies filtering policies.  OTOH, you may opt to
provide more optimal aggregation and allocate loopback IPs from the same
block as p-t-p IPs (per router, POP, region or other) such that less
information needs to be carried internally in your IGP (or BGP).

RFC 2519 provides some guidelines for inter-domain route aggregation.  A
slew of other documents and books provide IP address allocation guidelines
as well.

-danny


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