Auto-Discovering IPs of Switch Ports

[Jonathan Mast]

First of all, let me say that I'm not a networking expert and my terminology is probably a little off.

I have mrtg graphing a cisco switch, and it generates nice little graphs labeled "Traffic Analysis for N -- MY-SWITCH".

This is great except for the fact that I don't have (switch) port to host mapping, all the devices are at a colo.

I did run cfgmaker with each of the available ifref options, all of which didn't help much.

So my question is, can MRTG auto-discover the IP of the connected devices on the switches ports?

thanks




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[Petr Lázňovský]

AFAIK no. What mrtg only does is read the number of bytes which goes  through specified port by time period (switch itself count data, mrtg only read the sum) and put the numbers into graphs.

You or network admin should know, where is device witch specific IP and to which port of switch is connected.

L.

> So my question is, can MRTG auto-discover the IP of the connected devices on
> the switches ports?

> thanks

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[Petr Lázňovský]

I expect we are talking about L2 switch. The L2 switch working only with MAC address.

L.


> Well my thinking was: the switch obviously knows what host is plugged into
> which port, the question is then: is this info exposed via SNMP?  If so then
> MRTG should be able to extract it.

> 2009/10/20 Petr Lázňovský <[hidden email]>

>> AFAIK no. What mrtg only does is read the number of bytes which goes
>>  through specified port by time period (switch itself count data, mrtg only
>> read the sum) and put the numbers into graphs.

>> You or network admin should know, where is device witch specific IP and to
>> which port of switch is connected.

>> L.

>> > So my question is, can MRTG auto-discover the IP of the connected devices
>> on
>> > the switches ports?

>> > thanks

>> _______________________________________________
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>> [hidden email]
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[McDonald, Dan]

On Tue, 2009-10-20 at 11:57 -0400, Jonathan Mast wrote:

> So my question is, can MRTG auto-discover the IP of the connected
> devices on the switches ports?

No, look for "cammer", which might work.  I've hacked up my copy of
cammer beyond recognition so that it mostly works for me, with snmpv3
and weirdness and databases, but that's the appropriate tool to
correlate cam tables and arp tables.


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Daniel J McDonald, CCIE # 2495, CISSP # 78281, CNX
www.austinenergy.com


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[S Shipway]

Some javascript/style in this post has been disabled (why?)

MRTG just queries what its been told to graph, so it wont get anything like this.

 

Cfgmaker (the utility that generates the .cfg files for MRTG to use) will not do this by default, but with a bit of work it might be possible to make an interface template for your devices that pulls out the last MAC address seen on a port.  Mapping this to an IP would be a bit more work but not impossible, though you’d probably need something running constantly creating a mapping database?

 

The way we get around this here is that our Network people set the port description to be the hostname or IP of the device that is attached when they set up the port.  This way I can use the standard settings of cfgmaker to pull out the port description and use that for linking to the required host.

 

Steve

 

---

From: [hidden email] [mailto:[hidden email]] On Behalf Of Jonathan Mast
Sent: Wednesday, 21 October 2009 4:58 a.m.
To: [hidden email]
Subject: [mrtg] Auto-Discovering IPs of Switch Ports

 

First of all, let me say that I'm not a networking expert and my terminology is probably a little off.
I have mrtg graphing a cisco switch, and it generates nice little graphs labeled "Traffic Analysis for N -- MY-SWITCH".
This is great except for the fact that I don't have (switch) port to host mapping, all the devices are at a colo.
I did run cfgmaker with each of the available ifref options, all of which didn't help much.
So my question is, can MRTG auto-discover the IP of the connected devices on the switches ports?

thanks

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[McDonald, Dan]

On Wed, 2009-10-21 at 10:22 +1300, Steve Shipway wrote:
> MRTG just queries what its been told to graph, so it wont get anything
> like this.
>
>  
>
> Cfgmaker (the utility that generates the .cfg files for MRTG to use)
> will not do this by default, but with a bit of work

More than a bit.  the BRIDGE-MIB was implemented sub-optimally, so it's
a huge endeavor to make it go right.  The problem is that you have to
determine what vlan is associated with the port, then the BRIDGE-MIB
instance associated with the vlan, then you can start to hunt down mac
addresses.  And every instance of the BRIDGE-MIB has a separate snmp
community string or snmpv3 context-id...


>  it might be possible to make an interface template for your devices
> that pulls out the last MAC address seen on a port.  Mapping this to
> an IP would be a bit more work but not impossible,

Actually, that's easier, since ipNetToMedia is a mib that is laid out in
a sane fashion.

>  though you’d probably need something running constantly creating a
> mapping database?
>
>  
>
> The way we get around this here is that our Network people set the
> port description to be the hostname or IP of the device that is
> attached when they set up the port.  This way I can use the standard
> settings of cfgmaker to pull out the port description and use that for
> linking to the required host.

Yes, much easier...



--
Daniel J McDonald, CCIE # 2495, CISSP # 78281, CNX
www.austinenergy.com


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