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Re: BGP Question - how do work around pigheaded ISPs

  • From: Daniel L. Golding
  • Date: Tue Feb 13 00:44:10 2001

On Mon, 12 Feb 2001, John Fraizer wrote:

> On Mon, 12 Feb 2001, Bill Nickless wrote:
> > The question seems (in my opinion) to be whether registries are delegating
> > netblocks that can be further subdivided, or not.
> > 
> > That is, some ISPs hold that if a registry has allocated /16s in some
> > space, those allocations should not be subdivided by the allocatees.  If a
> > registry is allocating /19s minimum in some other space, then the
> > allocatees cannot and should not split that space and advertise longer
> > prefixes.
> All of this talk has me wondering about our network.  It's much smaller
> than most of yours and according to the CIDR report, the only thing it
> says we should aggregate is a single /24 out of the /19.  It is being
> announced for testing purposes and by the end of the week, the testing
> will be over and it will no longer be announced.
> My question however is along the lines of splitting the /19 up by swipping
> it out to BGP speaking customers who are announcing /24's, /23's, /22's,
> etc.  The announcement needs to be made by them (from my understanding --
> which may be wrong) for their multi-homing diversity to work.
> If I add an aggregate statement to our config, is it going to aggregate
> those /24's, etc that our BGP speaking clients are announcing to us into
> our main /19 announcement?
> This is something that I've been thinking about for a while and want to
> sure we're doing the technically sound thing.

There are two kinds of aggregates. Regular, normal aggregates, and summary
aggregates. Normal aggregates are announced in addition to any smaller
blocks that make up the aggregate. At least one smaller block inside the
aggregate is required to be present for the announcing router to announce
the aggregate (i.e. an activating route). Summary aggregates work in a
similar manner, but they surpress all advertisement of routes that are
included within the aggregate - they are subsumed. Both types of
aggregates should flag routes with the Atomic Aggregate attribute, to
indicate that there is the possibility of some routing information having
been lost. Be VERY careful with summary aggregates - if a customer is
sending prepends, you will lose that information at your border to your
peers and upstreams. Customers don't like that.

It is possibly to selective surpress subordinate routes belonging to an
aggregate on some router platforms.

> > In practice, how have corporate divestitures been handled by the
> > registries?  Have organizations with portable netblocks been able to split
> > them up and get new allocations from the registries, following the
> > corporate reorganizations?
> It is my understanding (again, perhaps flawed) that legacy allocations
> were settlement-free but, if an organization has say a legacy B, is only
> using a /18 of it and wants to do the right thing and return the B in
> exchange for an /18 in CIDR space, they now get to pay for the /18 just
> because they wanted to do the right thing.  I know if we had legacy space
> we'd hang on to it for financial reasons if none other.

If this were a just and sensible world, we would allow IP addresses to be
treated like property. Folks with big, wasted, /8s could sell them to
those who could or would use them. Because it would cost money to sit on
unused space, no one would. We would get much better
utilization. Considering the relativly large number of IPv4 addresses in
play, the price would be reasonable, especially once folks sold their
legacy space off.

> Someone correct me if I'm wrong on this.  
> ---
> John Fraizer
> EnterZone, Inc
Daniel Golding                           NetRail,Inc.
"Better to light a candle than to curse the darkness"