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

Fri Jun 6 22:58:15 UTC 2003

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.  :-)

Chris

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...
>
>Thanks,
>Dan
>
>On Fri, 6 Jun 2003 m.rapoport at completel.fr wrote:
>
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>
>>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,
>>
>>
>>
>>
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>>
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