[mrtg] Re: mrtg of Cisco routers via Internet fails

Merton Campbell Crockett mcc at CATO.GD-AIS.COM
Tue May 11 14:26:27 MEST 2004

On Tue, 11 May 2004 tom.voussure at sita.be wrote:

> But I have a problem with monitoring routers via Internet.
> I have several Internet connection. Some or completely separated from our
> main network.
> So to monitor these routers, i have to go thru a firewall, on the internet,
> to the other router.
> (mrtg server --> firewall --> INTERNET --> router)
> I always get the same error:
> --base: Get Device Info on xxx at
> SNMP Error:
> no response received
> SNMPv1_Session (remote host: "" [].161)
>                   community: ""xxx"
>                  request ID: -1222128975
>                 PDU bufsize: 8000 bytes
>                     timeout: 2s
>                     retries: 5
>                     backoff: 1)
>  at /usr/local/mrtg-2/bin/../lib/mrtg2/SNMP_util.pm line 570
> SNMPWALK Problem for on xxx at
>  at /usr/local/mrtg-2/bin/cfgmaker line 709
> If a try a snmpget i get also "Timeout, no response from ..."

The "no response received" indicates that the firewall is not configured 
to allow UDP packets

   (1)	from the "Internet" to the system that is running MRTG or
   (2)	to the "Internet" from the system that is running MRTG.

As UDP can be used for downloading malware, you don't want to allow UDP to 
cross over your security perimeter.  You need to construct specific rules 
that allow UDP port 161 traffic between your routers and the MRTG system.  
Also, be sure to specify the IP address of the router that is "nearest" 
the MRTG system.

Merton Campbell Crockett

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