Router gets 192.168.x.x for WAN IP!!! Why/how?

[Fat Tone]

My Dad got a shiny new lappy last week, and I finally persuaded him to get a router too. He is on NTL Cable and was previously using a Win98SE PC with a USB connection to the modem.

Router is Linksys WRT54G, modem is standard NTL-supplied. Laptop is running XP MCE.

I set everything up from scratch on Saturday so I know it was done properly. Ethernet and Wifi links to the router worked perfectly. On Sunday Dad calls and says he can't get on the net, using cable or wifi. We tried power-cycling with no effect. We looked into the router and sure enough the WAN IP was 192.168.x.x, no DNS IPs etc. I had him do a release/renew which fixed the problem.

He assures me he never connected anything up incorrectly.

So, how on earth can that happen (and survive power cycling)? Faulty router? ISTR someone on here finding that plugging your WAN cable into a LAN port on the router can bugger things up for everyone in your cable area, but I haven't heard of that for NTL here.

Any ideas?

[Tjalfe]

mine was getting 10.x.x.x when the actual cable connection was messed.. check that modem sync light is on, or whatever light it has to verify a solid connection

[Fat Tone]

Modem lights were all fine, inc. RDY going through its normal blink/solid cycle.

[ND66]

My router (Motorola) just got replaced last week. Good thing it was still under warranty.

The funny thing, the wireless connection was fine, the hard wire LAN connection got screwed up somehow. One of the lights where the cable was hooked up was always ON, even with the other end of the cable just hanging loose.
After doing a hard reset on the router, nothing worked anymore.

.

[gt40]

plugging your WAN cable into a LAN port on the router can bugger things up for everyone in your cable area, but I haven't heard of that for NTL here.

That would be my first guess.

@Tjalfe - when I had my WRV54G, if I enabled the VPN portion it would default to 10.97.X.X for the LAN (so when you log on to the other nework IP addresses don't conflict),
so it may seem that someone in the 'hood had a VPN router hooked up with the cables messed up.

Oh, unfurtonetly my entire network was fried during a lightning strike, so my WRV54 is in need of repair. Any Linksys/Cisco techs here
I'm thinking I may just need to replace the Xformer module.

[Tjalfe]

Mine was caused by squirrels having chewed the cable enough to let water in, causing bad attenuation.. damn squirrels. Once they repulled the cable, it never went back to the 10.x.x.x range, though I can still access the modem on one such address

[lowlifecat]

My Dad got a shiny new lappy last week, and I finally persuaded him to get a router too. He is on NTL Cable and was previously using a Win98SE PC with a USB connection to the modem.

Router is Linksys WRT54G, modem is standard NTL-supplied. Laptop is running XP MCE.

I set everything up from scratch on Saturday so I know it was done properly. Ethernet and Wifi links to the router worked perfectly. On Sunday Dad calls and says he can't get on the net, using cable or wifi. We tried power-cycling with no effect. We looked into the router and sure enough the WAN IP was 192.168.x.x, no DNS IPs etc. I had him do a release/renew which fixed the problem.

He assures me he never connected anything up incorrectly.

So, how on earth can that happen (and survive power cycling)? Faulty router? ISTR someone on here finding that plugging your WAN cable into a LAN port on the router can bugger things up for everyone in your cable area, but I haven't heard of that for NTL here.

Any ideas?

you say originally he was connected PC -> modem directly. then when you connected the router -> modem directly; the router was getting an internal IP...

are you sure the modem wasn't configured as a modem/DHCP router originally and that configuration stuck when you installed the router?

i've seen this before a lot. resolution: power cycle and do a release/renew. :U:

[Dilitante1]

ok, I'll bet his modem was in standby when he fired up the router getting the class C IP address.......typical of Motorola modems (and a common call into where I work)

1) have him make sure modem is fully up, and either refresh wan IP via the router interface, or hit his reset on the router to dump any settings in there

2)another issue might be that he is only allowed 1 device listing in the modem (mac address) and he may need to contact NTL to allow it to change to the router.....

[Fat Tone]

Update:

Got another call this evening with the same problem, so I went around with my router. His is the WTR54G V7 (I updated firmware to the latest and did a hard reset), mine is the WRT54GS V4. Lo and behold his connection was working when I got there!

I tried swapping the router back and forth, and powering the modem+router off each time. Mine never failed, his always got the wrong IP.

Then I tried connecting the modem direct to the laptop whilst watching the settings for the network adapter, and it was very illuminating!

What happens is the modem gives the laptop an IP of 192.168.100.10, with a lease period of 15 seconds. After that it updates to a proper IP address.

I surmise that the WRT54G boots up quickly enough to get the temporary IP, but is not refeshing its IP after the 15 seconds, rather some time later (as evidenced by the connection working when I first got there). I also did a test whereby I powered the router up about 1 minute after the modem and all was fine.

This is bolstered by the info I found at http://homepage.ntlworld.com/robin.d...ps/ipaddr.html, in particular:

"Note that, with the Surfboard and ntl:home 100/120, when the cable modem is not online to the cable operator's network, it runs an internal DHCP server which automatically gives the PC an IP configuration on the 192.168.100.xx sub-net to enable the PC to communicate with the cable modem on 192.168.100.1"

So, who is at fault here? I am also on NTL, and have a simillar (but older) modem, so we'll do a little more swapping around. If his router has the same problem at my house we'll consider swapping it.

Thanks for all the suggestions.

[Gurm]

A lot of cable companies do this (Comcast here does, if I turn my modem on the computer gets a 192.168.x.x for about 20-30 seconds). I'm guessing it's a firmware glitch that his router doesn't respect lease times.

[Helevitia]

I've heard of this before. Here is a possible scenario. It happens when somebody on your shared cable link plugs their cable modem into the LAN side of their switch. A DHCP request is reached from your WRT54G and the mis-cabled switch response accordingly. So somehow your DHCP request is being responded to by the other guys switch instead of NTL cable(I'm not sure if the request gets sent back to the provider or your cable modem is suppoed to respond?). Of course, this is all in theory. You could really find out by downloading Wireshark(formerly Ethereal) and sniff the wire. Look at what the MAC address for the responding switch and see if it is a Linksys or Dlink or some other common switch that may be sending out the response. If the mac address is a Cisco, Juniper, Motorola(possibly another cable modem), or other router, then it is probably coming from the cable company.

I've discussed this scenario at work and we concluded that this is a security risk since someone can act like your DHCP server and pretnd they are someone they aren't.. This could lead to password stealing, etc...

[Helevitia]

I just noticed that you mentioned what I wrote in your first post I missed that.

[Gurm]

No, here it's actually the modem diagnostic mode. If your modem never gets block synch, it will keep giving out 192.168.x.x so that you can HTTP into it and get the diagnostic information for the folks at the cable company...