[aprssig] Re: Help with DSL Modem. Try this...

Dave Baxter dave at emv.co.uk
Thu Oct 12 03:47:01 CDT 2006

One question, and an idea or few...

As the old setup...

What was the local DHCP server, the modem for the router's WAN port, or
the router for the modem's LAN port?  (My guess, the former)

You haven't got two local DHCP servers banging heads with each other
have you?  The other thought regarding X-over cables etc, these days
should not be a problem, as an awful lot of network routers switches and
the like will untangle that mess all by themselves.

The cable modems here (UK) usually act as a DHCP server to the LAN as
they see it, usually a single PC, but it can of course be a router's WAN
port.  (Most "consumer" stand alone DSL modems here, are usually USB
devices, with special software on the host PC, sadly not including a
firewall of any sort..)

The last time I added a router for someone on a cable ISP, so their
missus could use her wireless laptop elsewhere in the house, while my
friends PC was connected by UTP, we used an old Belkin cable/wireless (I
forget the model number) network router, with wireless on it's LAN side.

That cloned the MAC address of the existing wired PC (or any attached
device to it's LAN side if you asked it!) so it's WAN port (as seen by
the cable modem) had the same hardware address as the modem used to see
when that was hooked directly to the original PC.  Hooked it all up, the
cable modem accepted the "new" router without any fuss, while the
router's LAN side then acted as a DHCP server for the wired and wireless
PC's and all was sweetness and light.  (Yes, I implemented wifi
security, with a 128 random character key for WEP, yes I know that's
been broken, but it didn't have any WAP support, the user was happy,
even after I explained it all...)

I sort of tend to suspect the "new" router as well, as it's WAN port
should accept the modem as a DHCP source, but you may need to clone the
old routers WAN port MAC address, so the new router's WAN port has the
same MAC address, so the modem (more likely the providers systems) will
accept it as a valid end point, as they see it.

All this assumes that the "new" router can actually can do MAC cloning.
Not all can!  If so, it should be easy..

With no connection to the new routers WAN port.

Hook the new routers LAN side, to the old routers WAN port, straight
cable I suspect.

With a PC also connected to the new routers LAN side, find and go to
it's admin pages.

If you at some point turned off the new routers DHCP server, you may
have to manually set an address for your PC, and go and hunt with a port
scanner (angry IP scanner, Google for it) to find the routers IP
address.  If you can find that, see if there is a way to do a "Hard"
reset of the new router, to restore factory settings etc, that should
restore it's LAN side DHCP activity.

Once you have got into it's admin pages...

Go and find the page that shows the list of "Attached devices" and you
should see the old routers WAN port details, and those of the PC your
using.  If you can't see the old routers details, try a X-over cable for
that connection, but make sure the new routers LAN side is connected to
the old routers WAN port.  An easy mistake to make (been there, etc...)

No go and find the MAC cloning settings page (or whatever they call it)
and tell it to adopt the MAC address of the old routers WAN port as it
sees it (not that of your PC!)  As earlier, assuming the new router can
do MAC cloning!

It should then take the old routers WAN port MAC address, and apply it
to it's own WAN port.  You usually get at least one "are you sure you
want to do this" type of dialog.

If that all goes OK, then go to whatever page shows the WAN port status,
and you should see the new (old routers) MAC address now adopted, but of
course it will not be connected to anything.

Then, disconnect the old router, put the new router's WAN port to the
DSL modem, power up or reset the new router, and see what happens.
After a bit of light flashing etc, you "should" be connected to the
outside world now, so long as the DSL modem is happy with the DSL
connection of course, I guess there is an indicator lamp somewhere to
show that.  

If the modem seems happy (you can of course check using the old router)
but the new router is not happy, go back into the new routers admin
pages and see what it's WAN port status is.  (With it connected to the
modem of course!)  The cloned MAC address should be stuck in there, and
it should have been assigned an IP address by the modem/ISP.  If not,
check that whatever settings it has to allow it to act as a DHCP client
("Automatically get an IP address from the host", or some such) on the
WAN side, is enabled, and try again.

Of course, if you know what the old routers WAN IP was, you may be able
to manually set the new routers WAN IP to that too.

I think that just about covers it..

As others have also said, some providers systems will also accept a new
MAC address, if the old one hasn't been seen for some hours/days.  But
that's rare, even over hear (UK)

If all else fails, just call the provider, and tell them the WAN port
MAC address, of the new router.  It may take a few hours though, for
that information to propagate through their systems so it will accept
the new router.

All good fun, but very frustrating, that I know!  I have More T shirts
than I care to mention, from doing this stuff!  It's also a good way to
stock up on beer and wine, helping out friends and family, and their
friends etc etc...


Dave G0WBX.

Be interested to hear what the fix is, if this doesn't sort it....

> -----Original Message-----
> From: Mark Fellhauer [mailto:sparkfel at qwest.net] 
> Sent: Wednesday, October 11, 2006 4:29 AM
> To: TAPR APRS Mailing List; TAPR APRS Mailing List
> Subject: [aprssig] Re: Help with DSL Modem
> Thanks for all the responses.
> Here's what we did:
> A lot of resets and restarts.
> Tried new cables.
> Changed the LAN IP of the router to
> Tried an entirely different brand of router - a brand new 
> D-Link WBR-1310 (it failed to link also).
> Tried MAC Cloning.
> We pretty much covered what everyone has suggested.
> We did everything but wait a few hours as was suggested by one person.
> 73,
> Mark

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