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
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.
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
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
email@example.com Voice: 214.751.3881