Exchange point networks

Mon Jan 8 17:31:27 UTC 2001

Bill Woodcock writes:
> To expand upon that a little, while an exchange point itself is usually a
> layer-2 entity (that's a good thing), the ISPs which are exchanging
> traffic across it need to assign IP addresses to their router ports which
> are connected to it, and it's good to use a single common block of
> addresses for that purpose, and manage them in such a way that the in-addr
> DNS for the block provides useful information about which ISP they're
> associated with, and contact info, and so forth.  IP addresses are
> available for this purpose from Bill Manning, bmanning at ep.net, who also
> provides a management infrastructure for registering the in-addr names and
> contact information.

RIRs may also set aside addresses to be used for exchange points, and
you may want to check with your local RIR for this address space.  It
is generally a good thing to establish a relationship with the local
RIR in any case.

> 
>     > the ix provider may also choose to provide services on the side...
>     > Like other routed networks, if they are multi-homed, they tend to
>     > have their own asn.
> 
> One of the services that some exchange points choose to provide is a
> route-server or "looking glass" which is a router which all or most of the
> others peer with, and which either forwards routes between the other peers
> (aggregating the routes into single peering sessions) or allows
> participants to log in and see what routes other participants are or
> should be offering.  As a BGP peer, this obviously needs an AS of its own.
> Packet Clearing House, a research organization that I coordinate, offers
> free route-servers to exchange points, and we also provide the AS number
> for the route-servers.

There are actually several different services here, and I think it
would be useful if we had an agreed set of terms for those services.
Below I've put the terms I've heard most often and my sense of their
meaning; if there are other accepted terms or meanings, I would be
happy to hear of them and try to come up with a generic vocabulary.

One is a "route collector", with which exchanges participants peer in
order to give the exchange operator a view into what is going on at
layer 3 within the exchange; the primary use of this is to allow the
exchange operator to correlate layer 2 behavior with layer 3 behavior
when trouble shooting.  

Another is a "looking glass" which allows some group (ranging from
participants to the general public) to see layer 3 adjacencies and
some statistics for the exchange; this can be derived from data seen
by a participant at an exchange or from a route collector.

The third is a route server, whose function was originally developed
as part of the routing arbiter project.  The route servers allow
exchange participant to outsource the routing task (but not the
forwarding of packets) to a specialized host within the exchange.  

				regards,
					Ted Hardie