Re: More Questions of Exchange Points

[Ruomei Gao <gte489q () prism gatech edu>]

Ruomei Gao
Email: gte489q () prism gatech edu

On Sat, 6 Apr 2002 bmanning () karoshi com wrote:

> >     > 1, Some of the exchange points are layer 2 facilities, then why do they need
> >     > register IP addresses? Furthermore, those IP addresses do appears in the
> >     > traceroute traces (from the skitter data of caida). Does this mean that these
> >     > IP addresses are actually in use?
> >
> > Nearly all exchange points are layer 2.  This means that they consist of a
> > layer 2 switch, normally Ethernet, on rare occasions ATM or frame relay,
> > or even something more exotic.  The participating ISPs bring routers,
> > which they all connect to the switch.  Each of those routers must have an
> > IP address in order to communicate with the others, and the IP addresses
> > must all be within the same subnet.  That being the case, the correct
> > procedure is for a block of addresses to be allocated to the exchange,
> > rather than through any one of the ISPs, so that the rest of the
> > participants aren't dependent upon any one ISP which might be providing
> > the address space.  Also, that way no ISP is forced to provide transit for
> > the exchange-point addresses, which theoretically don't need it.
>
>       Er, -ALL- exchanges have a layer2 component.  Some institute
>       policy at layer 3.  Since, in general, we are talking about
>       INTERNET exchanges it makes sense that IP comes into play.
>       If there is a shared medium that is used as a single broadcast
>       domain, then a common subnet makes life easier for everyone.
>       It is possible to use divergent networks (see Sleepy Bills (woodcock)
>       list) on the same shared media.  His list argues that these
>       distinct subnets are unique exchanges.  My take is that they
>       are not but that is a nit argument.  There are lots of ways to
>       slice the exchange point.
>
> > So yes, those addresses are very much in use, but in somewhat the same way
> > that the /30 on a point-to-point link would be.  As a means for the two
> > adjacent routers to communicate, and pass on traffic which is coming from
> > and going to points much more distant.
>
>       What he said.  It is the Internet after all.
>
> >     > 2, How do you categorize the exchange points into large/local IXs,
> >     > transit/peering IXs (besides look into the peering policies)? From the number
> >     > of participants? Or from who are the participants?
> >
> > The difference between a local and a regional exchange is typically one of
> > size of participants.  It isn't a technical difference, so it might be a
> > little hard to arrive at complete consensus on, with respect to any
> > particular exchanges.  It's probably safe to say that in the U.S., PAIX in
> > Palo Alto, MAE-East ATM, and Equinix Ashburn are regional exchanges, that
> > in Europe the LINX and AMS-IX are regional exchanges, and that in Asia
> > JPIX, NXP-ISP2, and HKIX are regional exchanges.  They're where large
> > regional ISPs would go to peer with ISPs from outside the region.  A
> > regional exchange would often be thought of as one that an ISP from
> > outside the region would go to first.
>
>       only the very brave or very foolish will attempt such
>       catagorization.  Posh Bill (norton) clearly points out that
>       the value of an exchange, like beauty, lies in the eyes/network
>       of the beholder.  local/regional - peering/transit.... the
>       key thing is "whats in it for me?"
>
>
> > The difference between a peering exchange and a transit exchange is a much
> > more easily technically-defined difference: a peering exchange is one
> > across which, by and large, the participants just exchange peering routes.
> > A transit exchange is one across which many of the participants are
> > exchange full transit.  The consequences of this distinction are pretty
> > far-reaching, and generally mean that only one large peering exchange can
> > exist in a region, and it'll be inexpensive, whereas several smaller, more
> > expensive transit exchanges can coexist in the same region.  Phil Smith,
> > Keith Mitchell, and I will be presenting a paper on the topic at the next
> > NANOG in Toronto.
>
>       Humph. Difference w/o (significant) distinction.
>       If -ANY- isp provides transit off the exchange fabric,
>       does that make it a transit exchange?  If not, why not?
>
>       And what about exchanges that have -NO- routing protocol
>       at all?  (can you say ARP.... sure you can.)  Not peering
>       or transit.  Or are they?
>
>       For me, the key point is that an exchange acts as an aggregation
>       point for the participants.  Generating value off aggregation
>       can take many forms.  Peering and Transit are but two vectors
>       that are effected by aggregation.
>
>
> --grumpy bill (manning)