Wireless Woes and DSL Dilemmas

June 21, 2005 3:04 PM

Help me solve what the phone company (my DSL supplier) couldn't: getting my full wireless network running with a new modem.

Ok, I just got a new modem from the phone company, because the one I had since 2000 finally burned out. It's a nifty new SpeedStream modem, and I'm using Sprint. I also have a LinkSys 802.11b/g router serving the house.

Previously, the modem could not store username/pass information, so I had the router set on PPPoE so it would log in automagically for all network users. The new one stores the info by default, so I had the company walk me through the specifics of bridging the modem, allowing me to keep the router set the same. This worked fine, for about an hour.

After that it dropped off entirely, and wouldn't reconnect until I reset the modem and re-bridged, then cutting off again after another hour. I tried borrowing an identical router from a friend and setting it the same way, with the same result. I also tried using a different brand of router, no help. The actual DSL light on the new modem goes out, which further clears the router-being-the-problem angle.

Ok, so I thought I'd leave the modem set to its non-bridged form, and simply re-program the router. Auto DHCP wouldn't work with the new modem, so I was forced to use fixed IP. Presto! Or so I thought. Now if I have the router connected I get it cutting out after about an hour, but it works again if I unplug the ethernet cable between the router and the modem for, say, 30 secs then replug. That only buys me another hour. If, however, I plug it directly into the computer that resides at the same location as the router&modem, bypassing the router entirely, I get continuous connectivity. Unfortunately, this means the rest of the house is offline.

Also, the default settings for the modem include the internal address of the modem as 192.168.1.1 with its connected entity as 192.168.1.2, both standard internal network addys. The router was forcibly set to 192.168.2.1 so as not to conflict (really so I could troubleshoot without disconnecting the router). I have a theory that the failure is somehow related to the DNS, which the router has also set as .1.1, but I don't know what else to set it to and for that hour it does work fully at that address.

I couldn't think of anything more to include, so ask if you need some more data. Don't bother asking for my username or password, as I will give you a dirty look and god will kill a kitten.

posted by mystyk to computers & internet (4 comments total)

If, as you say, the DSL link light is going out, then either the modem or the DSL line itself is borked. You say you've tried a different router - have you tried a different DSL modem? If a different modem fails, then it's a line problem.

Also, you say it's a SpeedStream modem - Siemens SpeedStream? Odd little buggers, those things. Mainly because, as you've found, when something goes wrong they tend to lock up...

Thought: Possibly also MTU / MRU size related? In the Australian firmware (of the wireless versions at least) the MTU defaults to 1500, which is too big for the link and causes similar problems locking up after xx amount of time / data. Drop it down to 1492 or 1484 and see if the problems disappear.

(I forget exactly where the MTU is set - it's under the admin menu somewhere, and the default Admin username / password is helpfully shown at the top of the Admin login screen ;-)
posted by Pinback at 7:59 PM on June 21, 2005

Ok, one last thing, prompted by what you said. A technician who came over to help with this very problem said that the lines were some of the clearest he'd seen in 8 years of this work. Signal clarity was apparently damn near perfect, and interference between the multiple lines in our house was below measurable levels for his equipment. This leads me to believe it's not the lines.

I don't have access to any other modems. Period. It's provided by the company, and they wouldn't send out a new one unless you sent back the old one. Yes, it's one of those companies. Oh, and they were both Siemens SpeedStreams, just different models.

I assume that with the MTU/MRU you're referring to the router and not the modem, since you talk about wireless in the 'firmware' description. I hadn't really thought about that...I know a lot about networking, but I'm obviously no expert. This would at least make some sense since the modem works fine when hooked directly to a single pc. I'll check and get back to here with the result. Any other tips are still highly appreciated in the meantime.
posted by mystyk at 8:43 PM on June 21, 2005

Hmmm....

I actually meant the MTU setting in the modem - it's certainly there in the Aus firmwares when in 'routed' (username/password in the modem) mode, and I'm pretty sure it's still there in bridged mode. Reason I think it may be related to this is because wrong MTU sizes cause all sort of odd problems - "can't send large email attachments, but can surf OK", chunky / intermittent data flow, and, in the case of the Siemens DSL modems, lockups & dropping the link.

But you may be on to something with the MTU in your router. Try setting both the modem and router MTUs to 576 (common size for dial-up PPP links), and see how that goes. If you can't set the modem (I may be wrong about the setting being there in bridged mode), just set the router. If it works (other than the connection feeling slower), start at the other end and work down in steps of 8 e.g. 1492, 1488, 1480, etc.

Basically, there's a maximum packet size for the link, above which packets get either fragmented to fit in the smaller size, or rejected. It seems to me from my experience that the SpeedStream modems are prone to getting "swamped" when dealing with fragmented packets - they lose track of which fragments belong where, and lock up.

(Horribly non-technical description there, I know, but it's sorta true and serves the purpose ;-)

Oh, and don't believe what phone company techs tell you. They lie. I know, I am one (who gave up doing DSL installs because I couldn't handle lying to customers to cover our corporate incompetence...)
posted by Pinback at 12:38 AM on June 22, 2005

(Bah! Me can't count backwards in steps of 8! 1492, 1484, 1476, etc...)
posted by Pinback at 12:42 AM on June 22, 2005