[ILUG] PAN0 killing net

[Philip Creevy]

On Fri, 2009-07-03 at 08:42 +0100, Gareth 'bigbro' Eason wrote:
> Ian wrote:
> > what do you mean by L2-adjacent ?
> [snip]
> 
> 	While it's not quite a correct use of the term in this case, the
> implication is clear - for convenience (and to save routing table space
> and computation power) the internet IP space is broken up into networks
> and hosts - so:
> 	192.168.100.0/24 indicates to a router / computer that you have a
> network addressed as 192.168.100.x, and hosts potentially numbered 1
> thru 254 (allowing 254 hosts in a /24 network.)
> 
> 	Since you used a 24 bit netmask ( /24 or 255.255.255.0 ) you were
> effectively telling your computer that eth0 and pan0 were in the same
> network, and that any traffic bound for that network could be routed to
> either. (The actual priority used is rather more involved and depends on
> lots of other things.) This means that your computer would be equally
> likely (depending on a lot of things) to send traffic to your default
> route (and onwards to the internet) via eth0 or pan0, since
> 192.168.100.1 (possibly your default route) is accessible equally well
> from pan0 and eth0 - it's in the same network - and mostly in networking
> terms we'd make the assumption that it is also L2 (Layer 2) adjacent -
> it plugs into the same Layer 2 switch and can communicate with other
> devices in the 192.168.100.0/24 space without having to route. In
> technical terms, L2 adjacency means routing is not performed, and a MAC
> address is sought (via arp request) - a scenario likely to fail since I
> imagine your default route router is not really accessible from pan0.
> 
> 	I hope this helps - it's rather a simple concept once you know the
> background to how ethernet and TCP/IP works, but there's quite a lot of
> background there :)
> 
> 	If I can clarify further, please just ask. I've tried to throw in
> enough technical terms that you can use Google to find out more (if
> you're interested) but I hope I've explained things well enough that you
> at least can understand the basic concept. Do let me know if I've
> pitched at the right level or if I'm way off ;)
> 
> 	Best regards,
> 	-->Gar
> 
Your explanation was good, it does be so long between network 
setups that I do forget the basics and need to refresh my 
memory.
Thanks 
Philip