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Hiya Jonathan,
On 19-02-98, whilst lying in the gutter of the information super highway, I 
heard Jonathan Hunter whispering to Neil Croft about Frame Relay,
 NC>> My experience of Frame Relay isn't huge but ours all present on a
 NC>> standard X21 interface. Whether Linux can handle the concept of
 NC>> virtual paths properly or not I' don't know.
 JH> Um... Dumb question time, then. What are virtual paths?? :-)
You had to ask didn't you? =o)
Traditional point to point comms have one router port per destination with a 
fixed bandwidth. If you want to add another site, you have another link put 
in and add another router port. Frame relay has a single connection to the 
teleco. So long as the new site also has frame relay, all the teleco has to 
do is set up a PVC (Private Virtual Circuit) within their cloud and the 
router recognises it and uses it. Frame relay also allows a more flexible 
approach to bandwidth. You specify a minimum size for each PVC but you can 
use more than alloted. I beleive there are no guarantees ov successful 
delivery of packets over the specified bandwidth though. You also pay on a 
per packet basis. As far as I'm aware, FR nodes can carry a total of 2meg in 
the UK. If you want more then you'd need another node.
To sum up simply, instead of having a plethora of single lines between sites, 
FR is a link directly into a "cloud" with imaginary paths through it. As far 
as the end sites are concerned it matters not what route the packets take 
between sites.
I think that's about the sum of my knowledge.
 JH>>> to be getting one IP address, for a Linux box to use for IP
 JH>>> masquerading, can I assume that we don't need a fully-fledged
 JH>>> router?
 NC>> No. Even if you get X21 for the Linux box, what do you think it'll be
 NC>> doing?
 JH> Routing packets from the machines connected to the ethernet card, down
 JH> the X21 link??? Or isn't it that simple (and why not! :-)?
So you want it to act as a masquerading router? Hmmm, might work I s'pose.
 JH>>> Can we simply get a frame relay interface card for the Linux
 JH>>> machine, and plug the leased line direct into that??
 NC>> I doubt it.
 JH> OK, then.
I didn't say no, just I doubt it. It's the IP masquerading and routing 
software I'm not sure of. As a Firewall-1 engineer, I know it can be done but 
that's a pretty complex piece of software and very expensive. It's main 
advantage is I get to play with a Sparc 5 at work.
 JH> Well, the only thing is that no packets are *routed* by the Linux
 JH> box.. As we only have one IP address (and it'd be cheaper and more
 JH> secure to get only one IP address with the leased line) the Linux box
 JH> would be doing masquerading. Effectively it would be the only thing
 JH> connected to the WAN link, all the other PCs would be behind it. That
 JH> is why I thought it might be more sensible to have the router in the
 JH> Linux box, but obviously it's not actually that simple!
Damn site more complicated I'd guess unless there's a package out there.
 NC>> We all started somewhere.
 JH> I think I'm starting here, as far as X21 goes! :-)
X21 isn't a great mystery. It's merely a fast serial port. It's the PPP stuff 
running on top of it that might confuse. It certainly would me.
 JH> Thanks very much for your help,
Any time.
  /| /        neil.croft@capgemini.co.uk
 / |/eil =o)        2:250/410 @ fidonet
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