[mrtg] Re: RES: Testing testing + question.

Tue Nov 19 04:13:38 MET 2002

SNMP has nothing to do with your interfaces, directly.  I guess an ok
description of SNMP is it's like an array with keys and values.  The keys
are the OID numbers (.1.2.3.4.5.6...) and their matched up value.  When you
run cfgmaker, it uses a default OID for the bytes in and out on any
interface it finds from the device you query.  when you run snmpwalk against
a device, it will return ALL of the possible OID's (and their values, I
think).  With snmpget, you can feed in a specific OID and it will return
that OID's value.  check out the man pages of each of those programs (in
other words, RTFM - I love that phrase :)

so, the first thing you need to do (after you're sure an SNMP server is
running on the device you want to monitor) is make sure the computer you are
querying FROM can see the device you are querying.  Since you are querying a
firewall, now you really need to dig down into the system to make sure that
port (UDP:161) is allowed.  A lot of times firewalls are so explicit and
secure, they cannot talk to themselves, let alone allow another computer to
talk to it.

Once you have your device configured and responding to SNMP, run cfgmaker
against it - use all defaults.  So the cmd line would like something like
this:
./cfgmaker public at 172.16.0.1 > mrtg.cfg
that should make a file called mrtg.cfg.  If it doesn't, then check all the
above, plus community strings, which is like the password for SNMP.  There
is also the possibility that when your firewall was setup, the community
string "private" was given no privileges, or the READ,WRITE community string
was renamed.

I always recommend getting rid of a READ,WRITE community string, unless
there is a need for it.  So, have MRTG use the READ ONLY community string,
which usually defaults to "public."

Where does all this SNMP stuff get set?  In Windows NT/2000, it's under the
SNMP service in the services applet.  In the Linux world, I have no idea.
again, RTFM'ing should give you that answer.

Matt Walkowiak

----- Original Message -----
From: "Rowan Reid" <rreid at studio3arc.com>
To: "'ylf'" <ylf at uol.com.br>
Cc: <mrtg at list.ee.ethz.ch>
Sent: Monday, November 18, 2002 7:40 PM
Subject: [mrtg] Re: RES: Testing testing + question.

>
>
> > the device doesnt respond to snmp queries.
> >
> ok
>
> > if the device is a router or switch, make sure that the snmp
> > community is "private", and there arent a firewall blocking
> > the snmp udp requests (snmp uses udp:161 port), and if the
> > dev is not blocked to udp:161 requests -some cisco routers
> > wont accept by default those requests-.
> >
> The system is a firewall with a masquaraded internal net, and external.
> I imagine the snmp requests are beign generated on the internal nic, or
> lo which should allow all.
>
> > if the device is a server, check if snmp is already installed.
> > *nix: $ ps -ef |grep snmp
> Snmp is running.
>
> > +, try a "snmpwalker" like the *nix commands "snmpwalk" and "snmpget",
> > or a windows version for this, to make sure that the dev is
> > responding to snmp requests.
>
> I'm not very familiar with snmp whats an example command. Do I have to
> define a community. My ifconfig print out is below.
>
> eth0      Link encap:Ethernet  HWaddr 00:04:75:B1:3D:A9
>           inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:65508 errors:0 dropped:0 overruns:11 frame:0
>           TX packets:87068 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:100
>           RX bytes:6086853 (5.8 Mb)  TX bytes:101915853 (97.1 Mb)
>           Interrupt:11 Base address:0x6100
>
> eth1      Link encap:Ethernet  HWaddr 00:04:75:B1:3D:6C
>           inet addr:**.**.76.66  Bcast:**.**.76.71  Mask:255.255.255.248
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:97548 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:127715 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:6 txqueuelen:100
>           RX bytes:60841519 (58.0 Mb)  TX bytes:121950718 (116.3 Mb)
>           Interrupt:10 Base address:0x6200
>
> lo        Link encap:Local Loopback
>           inet addr:127.0.0.1  Mask:255.0.0.0
>           UP LOOPBACK RUNNING  MTU:16436  Metric:1
>           RX packets:220 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:220 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:20260 (19.7 Kb)  TX bytes:20260 (19.7 Kb)
>
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