[mrtg] GRE Tunnel mrtg traffic

Jay Hennigan jay at west.net
Mon Nov 2 19:58:30 CET 2009

Mohamed Sangey wrote:

> I  have configured GRE Tunnel for my customer. Also created MRTG graph 
> for it, but it misbehaves. I have fired mrtg config file for internet 
> traffic, which reflect normal. Only problem is that traffic which shows 
> VPN utilization.

A couple of things:  As others have suggested, verify the interface 
number is correct for the tunnel.  Usually an snmpwalk of the interfaces 
tree will give you the interface number.

Once you've done this, configure the router for persistent interface IDs 
so they don't get scrambled during a reboot.

In global configuration mode, enter:

    snmp-server ifindex persist

Also beware that tunnel interfaces have a default bandwidth of 9Kbits/s. 
  You'll want to set that to something sane, probably the bandwidth of 
the underlying physical interface over which the tunneled traffic flows. 
  In interface configuration mode on the tunnel interface:

    bandwidth 1536    (assuming a T1 physical path)

Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV

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