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Modem disconnects

cadbury
Newbie
Posts: 6
Registered: 03-09-2013

Modem disconnects

Hi,
Over the last week since getting fibre installed, I have had problems with the modem disconnecting and causing any active connections to be reset. I phoned up the technical support line about this and, as expected, was told there wasn't a problem because the exchange isn't seeing my line drop. As the upset is only for a few seconds, the modem is able to reconnect before the exchange has had a chance to realise that I've dropped and everything continues as it was before, with the exception of disconnecting any games I may be playing.
I tried this myself, to see if it really was the modem reconnecting too fast. I unplugged the DSL line from the modem for 5 seconds and then back in. All my active connections dropped but the router maintained the same IP and showed no loss of connection.
Here's the details from my router logs. The first set shows the logs from the PPP daemon and the second set shows that the router does see the WAN link go down and then come back up a few seconds later.
Last 500 PPP log entries
Sep 3 05:50:50 ppp: [wan_link0] LCP: no reply to 2 echo request(s)
Sep 3 05:50:40 ppp: [wan_link0] LCP: no reply to 1 echo request(s)
Aug 31 23:23:23 ppp: [wan_link0] LCP: no reply to 3 echo request(s)
Aug 31 23:23:13 ppp: [wan_link0] LCP: no reply to 2 echo request(s)
Aug 31 23:23:03 ppp: [wan_link0] LCP: no reply to 1 echo request(s)
Aug 28 08:48:26 ppp: [wan_link0] LCP: no reply to 2 echo request(s)
Aug 28 08:48:16 ppp: [wan_link0] LCP: no reply to 1 echo request(s)

Sep 3 05:51:06 check_reload_status: Reloading filter
Sep 3 05:50:56 apinger: alarm canceled: WAN(195.166.128.189) *** down ***
Sep 3 05:50:36 check_reload_status: Reloading filter
Sep 3 05:50:26 apinger: ALARM: WAN(195.166.128.189) *** down ***
Sep 3 01:25:39 dnsmasq[3403]: read /etc/hosts - 13 addresses

Now thanks to the joy of using a modem, I cannot view line stats or modem logs, both of which would be helpful in diagnosing the problem. To the best of my knowledge, there wasn't anything going on the line at the time that would cause a disconnect and the times do seem to be fairly random. Outside of these random losses of connection, the line has been brilliant. Absolutely no problems in getting the full line speed, both up and down, no matter the time.
What could be causing this? Is it a desync of the VDSL line due to noise? Is my IP Profile set too high?
10 REPLIES
Plusnet Alumni (retired) orbrey
Plusnet Alumni (retired)
Posts: 10,540
Registered: 18-07-2007

Re: Modem disconnects

Hi there,
Sorry to hear that. I've tested the line and the exchange logs are the same as our own RADIUS connection logs, and show a 6 day ongoing connection. Not disputing what you're saying above at all, but it does look like there's no fault from what we can see.
I'd recommend raising a dropping connection fault at http://faults.plus.net and including those router logs in the notes section at the end, that way our faults team will know what they're looking for. We'll be able to get it sorted for you.
cadbury
Newbie
Posts: 6
Registered: 03-09-2013

Re: Modem disconnects

I had a feeling you'd say that. I have reported the fault, mentioning what was in my original post as well as the logs from my router.
Community Veteran
Posts: 6,366
Thanks: 490
Fixes: 45
Registered: 30-07-2007

Re: Modem disconnects

Quote
I've tested the line and the exchange logs are the same as our own RADIUS connection logs,
but does ANYTHING log a VDSL drop ?
From what cadbury is reporting, it looks like the modem is losing synch, the ppp connection in the router is timing out on 2 lcp requests (30secs each), by which time the modem has resynched and so the ppp doesn't drop because it hasn't seen 4 lcp timeouts!. The RADIUS logs will only show ppp drops won't they ?
cadbury
Newbie
Posts: 6
Registered: 03-09-2013

Re: Modem disconnects

Speaking to a friend at work, he suggested it could be due to the weather and, looking at the times of the drops, that could be the case. He also suggested that it could be due to moisture on the line (early morning/late evening condensation) but it hasn't rained since I had it installed so I can't give anything more on that.
I'm a bit surprised that there isn't a way to get at the modem itself to look at the stats or logs on it. I'm confident that it is the modem losing sync for some reason; how long should I be able to disconnect for before the exchange realises I'm gone? I can always give that a test.
Community Veteran
Posts: 6,366
Thanks: 490
Fixes: 45
Registered: 30-07-2007

Re: Modem disconnects

Quote
how long should I be able to disconnect for before the exchange realises I'm gone? I can always give that a test.
I believe it's now up to 2 minutes, i.e 4 lcp timeouts of 30secs  see here http://community.plus.net/forum/index.php/topic,114808.0.html
cadbury
Newbie
Posts: 6
Registered: 03-09-2013

Re: Modem disconnects

It dropped twice this morning, within 20 minutes but still no disconnect from the exchange. Rather oddly, no entries in the PPP logs, just the WAN interface going down.
Community Veteran
Posts: 6,366
Thanks: 490
Fixes: 45
Registered: 30-07-2007

Re: Modem disconnects

It depends how it's detecting the WAN interface down. If it's using a timeout which is less than the LCP timeout (30Secs) and the modem resynchs with 30 secs then you won't see any ppp logs.
cadbury
Newbie
Posts: 6
Registered: 03-09-2013

Re: Modem disconnects

I see. Is that LCP timeout something that can vary between routers or is the 30s built in to the standard?
As the router runs on linux, I would expect that it is seeing the interface go down because the device on the other end (modem) has lost power (or been unplugged, but it's not that!).
Community Veteran
Posts: 6,366
Thanks: 490
Fixes: 45
Registered: 30-07-2007

Re: Modem disconnects

Quote
Is that LCP timeout something that can vary between routers or is the 30s built in to the standard?
Nope, it's set by the system at PN when the ppp link is negotiated. It used to be 2 mins but recently it's been reduced to 30 secs.
cadbury
Newbie
Posts: 6
Registered: 03-09-2013

Re: Modem disconnects

Well, even with the modem being down for 30 seconds, it still doesn't appear to be dropping from the exchange. The drop is happening every few days and the BT engineer that I was told would be arriving to replace the modem never showed up. Since I'm told every time I call that there isn't a problem (never mind that I watched the DSL light go out while on the phone to you), I've taken to manually disconnecting my router's PPPoE connection. Perhaps that will force the issue.
Edit: I would use a TBB graph to show the drops (it results in a large spike in packet loss) but they don't persist between IP changes.