Saturday, June 26, 2004
GINX: (G)rahamstowm (I)nter(N)et E(X)change
A mad plan© for running my own IX.
In spite of it's small size, Grahamstown has a large number on unrelated
computer networks. The small community nature of this town means that there
is a lot of interconnect traffic between these networks. For example,
several Rhodes students have Imaginet dialup accounts and use them to
connect to Rhodes. In the same way, Grahamstown Foundation staff have
spouses who connect through Rhodes, etc.
Off the top of my head the major players in Grahamstown are:
There might be others?? The numbers in brackets indicate the size of their
existing Internet links.
history
At this point a history lesson is useful. Originally there were very few
players in the South African Internet market -- they were all 'varsities and
Rhodes was one of the
first. Things progressed and Rhodes got its connectivity from the
Internet Solution. Tim Bouwer, who worked for the then Rhodes' computing
centre, was widely involved in getting school computing off the ground. He
arranged for some of the Grahamstown schools to connect to the Internet
through Rhodes.
With the advent of TENET, the schools
and Rhodes went their separate ways. All the schools, however, already had
leased lines into Rhodes' Struben machine room, so Rhodes leased them rack
space for the core of their network. This system is still in operation.
Each school is connected to the ASyNC core at Rhodes via SDSL
lines running at 512Kbps, and this core in turn connects to the Internet Solution.
The Grahamstown Foundation and Imaginet on the other hand both went entirely
their own route from the start, the latter because it was a commercial
enterprise. A few years ago, however, the department of Computer Science
needed Rhodes networking at the monument for a SciFest exhibit, so a tie line was put
in between the two. This tie line is still in place and is a RADSL line
running at 1Mbps/7Mbps. There is no such tie line to Imaginet.
interconnects
With all these tie lines running into Rhodes, you'd think there'd be some
intelligent routing in place to ensure that traffic takes the least cost
path. Not so.
St Andrews College, whose SDSL router is physically 1 metre away from
Rhodes' TENET router, is about 14 hops away from Rhodes following a route
that takes the traffic from Grahamstown to Durban to Cape Town to Port
Elizabeth and back to Grahamstown.
In the same way, the Grahamstown Foundation (whose line goes to UUNET, but have a tie line that goes
through the Struben POTS
crossconnect frame into the next building) is 13 hops away and uses a route
that goes from Grahamstown to Durban to Jo'burg to Cape Town to Port
Elizabeth to Grahamstown.
Imaginet, being a SAIX reseller, are somewhat closer. They're only 9 hops
away and the traffic only goes to Durban and back.
an Internet exchange
Which leads to where I'm going with this. It's be nice if we could set up a
Grahamstown wide Internet Exchange to handle all this interconnect traffic.
The obvious place to locate GINX is in the machine room in Struben Building
since three of the four players I've already identified have existing lines
that pass through this machine room.
The actual "exchange" part of an Internet Exchange is quite
simple. All we'd need to operate GINX is a managed layer two switch that's
capable of doing 802.1q virtual lans and a router capable of doing BGP4.
The switch doesn't have to be particularly great -- any switch that has
sufficient port capacity and can do vlans will do, which probably means
there is one lying around that we could use.
A router could either be a hardware router or a software one in the form of
a FreeBSD box running zebra (BGP
software). The latter means we could use an old PII or something, if we
were constrained to that sort of thing.
(We could buy this all new for around R15K — any benefactors?)
The network layout is best explained using a picture:
[ GINX Router ]
#
# FE + 802.1q
#
[ Managed 802.1q Switch ]
| | | |
+-------+ | | +--------+ FastEthernet
| | | |
[Rhodes] [ ASyNC] [Imaginet] [Foundation]
[Router] [Router] [ Router ] [ Router ]
| | | |
| FE | FE | ?? | xDSL
| | | |
[Rhodes] [ ASyNC] [Imaginet] [Foundation]
| | | |
| | | +------+
+----+ | +--+ | (all SDSL)
| | | |
[SAC] [KC] [VGHS] [GC]
In Rhodes' and ASyNC's case, the router in the diagram above might simply be
an interface on an existing router in the Struben machine room.
BGP
Some BGP-fu
would be required. We could do it without BGP since the routing won't
change that often. The disadvantage of this is that we won't get the sort
of redundant fall-over that BGP provides.
BGP lets us set up two kinds of routes: interconnect and transit. I'm not
suggesting that GINX provides transit routing merely that it provides a way
of interconnecting the existing sites.
This restriction makes GINX a lot simpler. For a start, because the routes
never propagate beyond the border routers of the participating sites, we can
use private autonomous
system numbers (ASN) rather than having to register real ASNs with IANA.
It also makes the politics of peering agreements very simple. Each site
provides and pays for it's connecting line into GINX. Rhodes (since it
doesn't have to pay for the line) could be asked to provide the hardware
necessary to run the exchange (not to terminate the lines though) as well as
a home for GINX in one of it's racks.
obstacles
The biggest problem as I see it in a plan like this is getting the other
players interested. The schools and the foundation are probably quite easy,
since there is an almost zero investment on their part (they already have
xDSL lines to the right place).
Imaginet and other local ISPs are more complex. They'd have to put in an
extra line to Rhodes, which would cost them money. David pointed out that
they'd also have more difficult decisions to make ... They could get Telkom
to put in a DigiNet circuit, whichh would guarantee them bandwidth and
stuff, but would be expensive and at a fairly low bitrate. They could run
xDSL or some equivalent over a Telkom analogue leased line, but there is
risk in that (Telkom don't necessarily approve for example).
If they go the DigiNet route, they'd need to work out whether it's worth
their while to route their traffic over a low bandwidth link to Rhodes (say
128Kbps) rather than use their higher-bandwidth external lines (at say 1Mbps
in Imaginet's case). They'd also need something that talked high-speed
serial at each end, which means a real router which is expensive.
If they go the xDSL route a lot of things become simpler. Bandwidth is
higher, so the routing decisions are a lot easier. Most xDSL routers/modems
give Ethernet out, so connections are easier. The line itself costs less.
The only problem is that there are no guarantees as far as Telkom goes.
GINX?
Or GIX or SCIX or SCINX (settler city). Any other suggestions?
The best pronouncation I've have for GINX at the moment is with a G as in
gist - jinx. That might be confusing since there is already a JINX. It could also be a hard G as in
Guy, since it's Guy's idea ;-)
posted by guy at: 10:46 SAST |
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