North American Network Operators Group

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Re: ISP operational question

  • From: Stephen Stuart
  • Date: Tue Dec 12 23:15:48 2000

> A new company wants to become a regional ISP. This company will purchase one 
> or two large bandwidth circuits from a NSP of their choice.

Suboptimal, but as you note that the preferred alternatives are not
feasible we'll press on.

> Then the new regional ISP will offer private line p2p Internet service to 
> regional businesses. Basically, this is a small operation.
> Now here is the question. What choices does the regional ISP have when 
> implementing routing and IP addressing? I assume the regional ISP will not 
> implement BGP, since there will only be one maybe two upstream connections 
> to a single NSP - initially.

Your choices are BGP or static. Using static routing becomes a poorer
choice in the face of multiple upstream connections, but is
technically possible. 

If you are dual-homing to get redundancy *and* you want to be able to
get use out of both circuits, then you really, really, really want to
be using BGP. There are options if using a static default, but you
really want to be using BGP.

> Furthermore, I assume the NSP would provide the regional ISP with a supernet 
> - say a /20 or so. Then the regional ISP would allocate subnets of the 
> supernet to their customer - say /24s.

You might find an NSP that would give you a /20; slow-start, as noted
by a few others. They'll certainly allocate you some space, though,
and give you more if you use up the first dose.

> I also assume the regional ISP would not require an AS number since they are 
> not implementing BGP. Basically, all traffic from the regional ISP and 
> customers is default routed to the single upstream connection.

Correct. You only need an AS if you run BGP.

If you are avoiding BGP because you don't want to go get an AS number
from ARIN, you can ask your upstream provider if they either can
support peering with you using a private AS number (64512-65535), or
if they keep an AS number for singly-homes customers.

> Are these assumptions valid? Is this a good configuration? I realize 
> multiple upstreams from different providers is optimal, however not 
> plausdable in this case.

Validity of assumptions is noted in-line. This is not a good
configuration, but you go right on to say that the necessary building
blocks for a good configuration are not available to you.