You are probably using "bridge" mode because the DSL modem you have is not
just a modem, it also has a built-in router. Placing the router in bridge
mode disables DHCP, essentially disabling the built-in router.
DSL companies started putting routers in their modems to prevent the problems
they were having with naive customers connecting the modems directly to their
PC without using a router (BAD idea), thus running without the NAT (Network
Address Translation) firewall a router provides. While adding the router was
a good move for customers that had no other router, it obviously complicates
things a bit for those that do.
The reason you haven't seen this issue with cable modems is that most cable
modems *don't* include a router, although there are now some that do such as
the Motorola SBG900:
http://broadband.motorola.com/consumers ... efault.asp
When using cablemodem/router combo with another router, you'd have the same
dual-router setup as you do with your DSLmodem/router combos.
BTW, another way to handle the dual-router issue is to use the one in the
modem (turn on DHCP), and disable the other router (turn off DHCP), thus
turning the 2nd router into a simple switch and/or WAP (Wireless Access
But perhaps the best way to use two routers is to have them both actively
running in a nested connection, setup with non-conflicting addresses. I've
done this as a way to effectively create a network within a network, an
"open" one for guests, and a closed one for myself.
By connecting the second router to the first one you could set up two
networks (each with wireless access as well), the first using unsecure WEP
protection for guests (and crummy devices that don't support WPA), and the
second one with unbreakable WPA protection for sensitive files, systems, etc.
Any systems on the outer open network cannot "see IN" through the 2nd or
nested router, therefore any systems or shared files/printers on the nested
secure network are completely inaccessible to devices on the open network.
However, note that devices on the secure closed network CAN "see OUT" through
the nested router and access any device on the open network. This dual setup
also means that when a guest comes over and needs internet access, I only
have to give them an unsecure WEP key (or plug them into the open network
directly). I don't have to give them my secure WPA key, and whether they are
wired or wireless I don't have to worry about them accessing any of the
systems, files or printers on the closed network.
As for client network testing issues, again I'd stress that known-good spare
equipment is by far the most cost-effective test gear for individuals or
Re: the password issue, I would tell the client in advance that you'll need
the password, or you'll have to charge them for the time it takes to call the
provider and have it reset on the job.
Once you identify a suspect component, merely replace it with the known-good
spare you brought along. If the replacement works, offer to sell them the
working equipment as the solution (I recommend charging at least a 25% markup
on all hardware and software you sell). If they refuse, then simply charge
them for the diagnostic time, and remind them that future work on the same
problem will be billed by the hour, which can add up fast.
As for the "black hole" wireless problem, that is probably caused by
interference on the 2.4GHz band from cordless phones, microwave ovens, other
wireless networks, bluetooth devices, radio transmitters, etc. The best
solution in that case is a switch them over to the 5GHz band using an 802.11a
WAP and NICs. Have a set with you so you can demonstrate functionality, then
once you demonstrate that it works, sell it to 'em. Sure the 5GHz stuff is
more expensive than 2.4GHz, but the 5GHz stuff works where the 2.4GHz doesn't.