Nagios XI: Monitoring Cisco 877 ADSL Router

We have couple Cisco 877 ADSL routers in some remote offices. To verify the ADSL line works properly, we add the routers into our Nagios monitor list.

SNR (Signal to Noise Ratio) and Attenucation are two key measurements that tell you the performance of the ADSL line:

  • SNR reflects the signal strength to the level of noise on the line. The higher the SNR value is, the better performance you get. As there is less background noise. It is measured in dB.

      6dB or below is bad and will experience no synch or intermittent synch problems
      7dB-10dB is fair but does not leave much room for variances in conditions
      11dB-20dB is good with no synch problems
      20dB-28dB is excellent
      29dB or above is outstanding

  • Attenuation is the term used to describe the reduction of the ADSL signal strength that occurs on the copper pair over distance. So the lower the attenuation value is, the better performance you got. It is also measured in dB.

      20dB and below is outstanding
      20dB-30dB is excellent
      30dB-40dB is very good
      40dB-50dB is good
      50dB-60dB is poor and may experience connectivity issues
      60dB or above is bad and will experience connectivity issues

To add the ADSL router into the monitor list, you can follow the Nagios XI monitor wizard and choose the SNMP monitor. Then make Nagios to monitor the following OID.

SNR in/out: . / .
Attenuation in/out: . / .
Outputpwr in/out: . / .
Linespeed in/out: . / .

The following are the performance graphs in my Nagios XI. The unit is 0.1 dB.



3 thoughts on “Nagios XI: Monitoring Cisco 877 ADSL Router

  1. Jackie,

    Are you familiar with a way to have Nagios pull an IP address of a specific interface on a cisco router? We are using Cisco 861 routers at remote locations that use an ADSL connection and we would like to have Nagios pull the IP address that the FE4 interface pulls from the ISP and log it for troubleshooting. Thanks.

    1. Yes, you can. Use mrtg to pull the interfaces information from the router’s LAN interface, then get the IP address of the WAN from the mrtg configuration file.

      Here is an example:
      1) /usr/bin/cfgmaker –show-op-down –zero-speed=100000000 –snmp-options=:::::1 –noreversedns community_string@ >> /etc/mrtg/mrtg.cfg

      # more info about cfgmaker can be found at:

      2) Open /etc/mrtg/mrtg.cfg to find the info of the WAN interface.

      3) Add a service in nagios by creating /etc/local/nagios/services/ And add something based on what you found in step 2). It should be something like this:

      define service {
      service_description FW_OUTSIDE Bandwidth
      use xiwizard_switch_port_bandwidth_service
      check_command check_xi_service_mrtgtraf!!11,11!28,28!K!!!!
      # 14 is the interface id, replace it with yours.
      max_check_attempts 5
      check_interval 5
      retry_interval 1
      notification_interval 60
      contacts nagiosadmin
      _xiwizard switch
      register 1

      Hope it helps.


  2. Thanks Jackie. I will look into this. We would like to do bandwidth monitoring as well but I think with having our Routers connected to DSL modems that are in bridge mode via a Cat5e patch cable will throw the bandwidth utilization graph off as I dont think it will be pulling the proper bandwidth of the DSL line, instead it will be registering the 100 mbps link of the DSL modem’s lan interface that we connect to. Getting the IP of the WAN(dialer 1) interface is definitely going to be a huge help if that works. thanks again.

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