Cisco 857 dropping connection on ADSL2+ line

Unanswered Question
Jul 31st, 2009


Just over a week ago this forum helped to resolve a problem whereby a Cisco 857 could not connect to the internet following an upgrade to ADSL2+

The router was working fine, then dropped the connection. The router is no longer connecting, yet when it is swapped for a Netgear 834, it connects straight away.

Can anyone recommend any tests or settings I can check. Nothing has changed in the configuration, and as far as I know, nothing has changed on the ADSL line.



I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Fri, 07/31/2009 - 12:11

Hello Nick,

in the DS downstream direction

Noise Margin: 0.0 dB 22.0 dB

Output Power: 20.5 dBm 12.0 dBm

Attenuation: 19.0 dB 8.0 dB

noise margin is 0 means no possibility of transferring data without errors.

It appears the ATU-R that is the modem in the router sees a weak signal coming from the central office ATU-C.

But the signal is not really weak or also the other modem would not synchronize.

I would do the following test:

power off the cisco router for some hours let it to cool then try again.

Hope to help


nickc1976 Thu, 08/13/2009 - 07:17

Since the connection was being dropped by the Cisco 857, the customer has been using a Netgear 834 without any connection issues. Today, I swapped the Netgear for a new Cisco 857.

The connection worked for about 2 hours, then started to drop again (see attached results for a ping to the external ip address)

I also did a show dsl interface atm0 again just after the connection dropped, also attached.


Giuseppe Larosa Tue, 08/18/2009 - 09:07

Hello Nick,

this time the sh dsl interface looks like good enough specifically no errors are present.

The question may be related to some other issue for example cpu and memory resources used by NAT or execessive ARP traffic if a default gateway ip address is missing or simply the noise margin is at a border line.

I can say we have some DSL lines showing this kind of behaviour.

We have roughly 100 remote sites with ADSL lines making ipsec vpn over the internet.

It wold be nice to see what the noise margin is with the netgear.

I see 31 -30 db noise margin on ADSL lines (not adsl2+) (we have some ADSL2+ lines but most are still ADSL)

Hope to help


Ian Cowley Fri, 10/09/2009 - 01:19

We're having similar problems with 877s.

if you do a 'sh int atm0' you will see drops and 'sh buffers' will show failures in the Middle and Big buffers.

have used 3.0.33 and 4.0.15 dsl firmware

nickc1976 Fri, 10/09/2009 - 04:11


We went out to this customer today. I have attached the Netgear stats.

Strangely, when we connected up the Cisco, it worked! We have left it in place over the weekend, so will see how it has coped on Monday.

Giuseppe Larosa Fri, 10/09/2009 - 10:11

Hello Nick,

the Cisco router has negotiated a lower DS bit rate 15346 kbps but with an higher noise margin 6.5 dB.

netgear is using 24032 kbps but with only 3.2 dB noise margin.

let's see what will happen.

each line is different and the customer line looks like better then the other one.

Hope to help


nickc1976 Wed, 10/14/2009 - 07:17

Hi Giuseppe

The Cisco router lost the connection again on Monday, so we had to swap it for the Netgear again.

I have attached the output of "sh dsl int atm0" which was taken this morning. At the time, the Cisco was unable to connect. Swapping to the Netgear gave a connection straight away, so I have again attached the Netgear stats.

Is there anything I can do to keep the Cisco connected?


Giuseppe Larosa Wed, 10/14/2009 - 10:31

Hello Nick,


Noise Margin: -5.5 dB 5.0 dB

Output Power: 18.5 dBm 12.5 dBm

Attenuation: 18.0 dB 8.0 dB

Defect Status: LCD LOM LOS LOF LCD

with a noise margin of -5.5 dB and BER of order of 10E-0 there is little you can do.

you see there is LOS = Loss of Signal

LOF = loss of frame

LCD = loss of cell delineation.

or really this device performance becomes worse over time (thermal effect) or it is defective in something.

Netgear shows the same numbers as last week with a noise margin of 3.3 dB.

you should ask to the provider to use a fixed rate profile at 10 - 12 Mbps this may provide stability for the line.

We had actually to ask speed reduction in some cases to get a more stable link (changing the device to a netgear was not an option for us)

Hope to help


nickc1976 Fri, 10/23/2009 - 05:26

Thanks for the advice.

Do you know why it is that the Netgear can get a stable signal, but the Cisco cannot?



kmccourt Mon, 10/26/2009 - 06:21

Not sure if this will help but Cisco have just released an updated firmware 4.0.18 for the 20190 ADSL chipset used in the 857/877. This fixes some specific interoperability issues with certain BT DSLAMs. It may be worth checking out.

"ADSL firmware release 4.0.18 is the recommended firmware release to use on CPEs connecting to BT's network for ADSL2/2+ service. It should only be used to resolve ADSL2/2+ interop issues while connecting to the BT network. This release solves issues described in the following DDTS: CSCta54059, CSCta54040, and CSCtb31105."

LordFlasheart Tue, 11/17/2009 - 06:31

This is good news. Hundreds of those nasty little 877s getting migrated over to 2+ and had nothing but problems.

LordFlasheart Tue, 11/24/2009 - 07:07

We have other cisco ADSL routers out there. Just wondering how they are affected by ADSL2+?

2611XM using ADSL WIC

2811XM using ADSL HWIC

I have a feeling that the 2600s won't be able to support 2+ and the 2811s will only support 2+ with Service Provider IOS. Can anyone confirm this?



This Discussion