[mrtg] Re: Newbie questions

Matthew Petach mpetach at yahoo.com
Fri Sep 24 20:12:52 MEST 2004

--- Ron Crummett <roncrummett at mail.caynetco.com> wrote:
> Hello all - 
> I have been asked to monitor traffic on a remote router for one of our
> clients, using MRTG.  I have learned the basics of setting it up but when I
> tried running it on the router in question, I got this message:
> SNMP Error:
> no response recieved
> SNMPv1_Session (remote host: "" [].161)
>                   community: "public"
>                  request ID: 794746515
>                 PDU bufsize: 8000 bytes
>                     timeout: 2s
>                     retries: 5
>                     backoff: 1)
>  at C:/MRTG/bin\..\lib\mrtg2\SNMP_util.pm line 627
> SNMPWALK Problem for on public at at
> cfgmaker line 827
> WARNING: Skipping public at as no info could be retrieved
> I am in a unique position where I have not studied networking until now, so I
> am learning on the fly.  From what I have been able to find, I have two
> conclusions:
> -SNMP is not turned on on the router
> -the community string is wrong

Pretty reasonable guesses; there could also be an Access Control List (ACL)
blocking UDP traffic to port 161, and one should never rule out simple
issues like "is the router turned on/plugged in?"

The IP address is pingable from here, so we'll figure
you have good IP reachability to the device; so leaving
the ACL possibility aside for the moment, the next step
is to check and see if SNMP is configured on the device.

It appears to be a Cisco router; if you have the passwords
to the router, the first step is to log in and become
enabled; to do so, after logging in, if your prompt
does not end with the # character, type "enable"
and then type in the enable password for the router.

Once enabled, you should be able to type
"show run" 
to see the configuration on the router; you
are looking for lines with "snmp" in them.  If
you are running a recent enough version of IOS,
you can speed up the process by typing
"show run | include snmp"
that will show you just the lines that have "snmp" in

If you *don't* see any lines of the form
snmp-server community BLAH
then SNMP isn't enabled on the router.  To
enable snmp, type
configure terminal
snmp-server community your-SECRET-community RO
write memory

This will enable SNMP with the read-only string
that you replaced "your-SECRET-community" with.

Later on, you can specify an Access Control List
on the line to limit which IPs can do SNMP queries
against your device; but to start with, leave the
ACL off until you've verified you can poll the

For now, go back to your MRTG box, and replace
"public" with the SNMP community string you
put on the router, and try doing your polling
again.  With any luck, you'll find that it
succeeds now.

> My problem is that I don't know what to do about either of them.  The router
> in question is located about two hours away but I'd really prefer to not
> drive down there for something like this, when it seems to me that I should
> be able to do it remotely.  I just have no idea how. 
> I apologize if this does not make sense, or if it is answered in the
> documentation.  My problem right now is that as a learner, I have no idea of
> where to start.

No need to drive.  :)

> That's it from here.  More to come as the plot thickens...
> Ron Crummett
> CayNet Consulting
> (208) 424-1590 office
> (208) 850-6589 cell
> http://www.caynetco.com 

Hope this helped!


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