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Re: Customer AS

  • From: Curtis Villamizar
  • Date: Fri Aug 16 19:11:21 1996

In message <199608162135.QAA07812@ns1.computek.net>, "Chris MacFarland" writes:
> Tim Crowell (GTE.NET) wrote-
> 
> > 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.
> >
> I would make them renumber with a new class c that was not in your CIDR
> block.
> Maybe they could get a class C from the swamp?

Are you suggesting that all dual homed networks should be renumbered
such that they can't be aggregated and can't be reached from a good
part of the Internet.  I don't think that is a good idea.

Are suggesting punishing a customer for picking up a second provider
by giving them an unroutable prefix?  I hope not.

> > 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
> 
> No you would just advertise the aggregate CIDR block, they
> should advertise the more specific route so when you
> peer with them their route is propagated with their AS number.

I think it is assumed that GTE would be passing on the route heard
from the customer.  The difference is they would not be passing on the
more specific routes they learned from single homed customers in the
same blocks, or customer multihomed to them.

> > 4. XYZ will announce the class 'C' as a /24 only.
> 
> XYZ should peer with them just as you have done.

Same comment.  Announce does not mean "configure a static route".

> > 5. Both GTE and XYZ will supply a default route.  
> 
> If the client is carrying the full routing table should be default free,
> if they chose not to then they will have to decide on which provider
> should be the default route.

There is no harm having a backup.  They should not try to load split
across the two default routes unless they want extremely poor TCP
performance.

> >  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.
> > 
> >
> Now you understand why everyone is using Cisco 7500 series routers
> with 64 to 128 megs of RAM.

I think the percentage of dual homed /24s is small compared to the
number of prefixes that have not been aggregated with no good reason
at all.

Curtis
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