Customer AS

Curtis Villamizar curtis at
Fri Aug 16 01:11:13 UTC 1996

In message <32137AD8.4828 at>, Tim Crowell writes:
> Howdy folks,
> I would like to pose a question to the group about the best way 
> to implement the following;
> GTE has a customer who is a content provider that we have 
> allocated a class C out of our CIDR block.
> They have subsequently also ordered a second transit service 
> from ISP XYZ.
> Our assumptions are:
> 1. Customer will obtain an AS number to do BGP with both GTE and 
> XYZ.  
> 2. BGP will be established with both ISPs
> 3. GTE will announce the class 'C' as both a part of our 
> aggregate CIDR block and as a specific /24. 
> 4. XYZ will announce the class 'C' as a /24 only.
> 5. Both GTE and XYZ will supply a default route.  

OK so far.

> Explanation/Questions;
> 1. Does this AS number have to be an officially registered AS or 
> can it be a reserved number?  The thought is that the Class 'C' 
> will be announced by both ISPs and strip the customers AS.  The 
> AS would only be used to connect between ISPs.
> It seems extremely wasteful for every little company that wishes 
> a dual homed network would have to get a registered AS.  

If it is a reserved number you and the other provider would have to
get it out of the AS path before passing it along.  The would then be
no loop detection if you pass the /24 to XYZ or XYZ passes the route
to you, so you can't get rid of the AS and can't use a private AS.

If the customer was dual homed to you, you could give them a private
AS (and get rid of it) if it were more convenient for you to do so.

> 2. We first had major heartburn with carving the 'C' out because 
> we just couldn't see having to add 2 additional announcements to 
> the internet routing tables but we have come to the conclusion 
> that there is no other way to do it. We assume that we have to 
> announce the /24 in addition to our aggregate otherwise XYZ's 
> more specific announcement of our network would route all 
> traffic through them from the internet.  It just seems that if 
> there were a large number of these multi-homed Class 'C's that 
> the internet routing table would be flooded.  (Maybe thats a 
> part of the problem.

This is not a big deal (don't forget to put the route object for the
/24 into the IRR).

> 3. As a followup,  what would you do if a subnetted class 'C' 
> customer  who only requires a dozen or so addresses but orders 
> connections to two ISP's.  Do you burn a whole Class 'C' ????

Quite frankly, in most cases I'd burn the class C.  If this is a
primary and backup relationsship, and you were primary you could use
use >/24 as long as you don't mind taking the traffic and passing it
to XYZ to accomplish the backup (that also may not be what the
customer had in mind for backup so you're back to the /24).

> 4. Is there anyway to accomplish what the customer wants that we 
> haven't considered.

I think you have the best setup as is.

> 5. I understand that we will have to submit the Class C to RADB 
> and create a "hole" in our aggregate to effectively represent 
> the network topology.

I don't know if other use the "hole" field in the route object.  We
just configure the more specific if there is a route object for it,
regardless of whether there is a prefix overlapping it.

> Thanks for any assistance,
> PS.  If i'm just being stupid about this feel free to say so.  I 
> don't pout too long.

These are good questions for NANOG.  Its all about issues where
providers need to communicate and cooperate.

> -- 
> Tim Crowell - GTE Intelligent Network Services
> tcrowell at		Voice: 214.751.3881


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