[Gllug] [slightly ot] ADSL config fun

[Chris Bell]

On Tue 17 Sep, Matthew Kirkwood wrote:
> 
> Hi,
> 
> This is slightly off-topic, but there seems to be more
> tame networking knowledge here than most other places,
> and I don't doubt that someone here has a similar config.
> 
> My ADSL was activated yesterday and seems to be working
> OK.  However, I'm having some issues trying to convince
> my D-Link 504 router to run non-NATted.
> 
> With NAT enabled, I can see the outside world (though it
> does seem to have absurdly low connection timeouts).  If
> I disable NAT and try to put the ethernet interface onto
> my IP block (xxx.yyy.zzz.126/29) it refuses to accept a
> LAN IP on the same block as the WAN one.  So I down the
> WAN link, reconfigure and re-connect (or force it via the
> CLI).
> 
> Now, I get ICMP redirects from the router suggesting that
> packets go out via itself.  I've lost the tcpdumps, but
> they look roughly like:
> 
> udp xxx.yyy.zzz.121:<N> => ns1:domain: www.dlink.com?
> icmp xxx.yyy.zzz.126 => xxx.yyy.zzz.121: redirect to xxx.yyy.zzz.126
> 
> Am I being stupid here, or is the router IP stack really
> badly broken?
> 
> Cheers,
> Matthew.
> 
> 
   I have been told that an ADSL box connected to a BT line must have its
own official IP address because of the complications involved in PPP over
ATM. I understand that the ATM data packets are all 48 Bytes, with control
data packets travelling a parallel route through the BT network. The ADSL
box has to convert between the ATM and Ethernet packets, and can only route
data direct to computers in your network without NAT if you have additional
official addresses for those computers.
 My ASUS box (Alcatel chipset) can be configured as a transparent router
(with control via a separate serial interface) but only if BT had provided
PPP over Ethernet. I only have the one official IP address, so have no
choice about using NAT, although I may be able to do useful things with port
forwarding.
   There are some PCI ADSL cards around, and I have been told that more
should be available soon from a company which has supplied Linux drivers
with its kit. These may give much more control in a router/firewall box.

-- 
Chris Bell


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