Strange behavior with MRTG

Hey all,

I have a linux box as a firewall for a small network hosting a website,
and I'm trying to measure the traffic using MRTG but something wierd is
happening. There are two nics in the box, once is connected to the internet,
one internally, pretty standard config.

I'm running MRTG from cron on the box itself (probably not good for a
firewall box, but just work with me). I have the SNMP daemon working, and
configured for localhost, external and internal interfaces, and everything
seems to work fine. snmpwalk's work and everything. However it appears that
everytime MRTG runs from cron, I lose access to the network momentarily from
my dsl at home to the external interface on the firewall.

MRTG is running from localhost, and connecting to the snmpd running on
the external address of the firewall. So... uh... the only thing I have come
up with is that when MRTG runs, it's taking all the bandwidth in the snmp
poll on that interface, not allowing me to connect until it's finished? Does
this make sense?

If so, is there a way to connect to snmpd on localhost, and have it
gather information for another interface?

Eric

Eric Gibson wrote:

> Hey all,
>
> I have a linux box as a firewall for a small network hosting a
> website,
> and I'm trying to measure the traffic using MRTG but something wierd is
> happening. There are two nics in the box, once is connected to the
> internet, one internally, pretty standard config.
>
> I'm running MRTG from cron on the box itself (probably not good for a
> firewall box, but just work with me). I have the SNMP daemon working, and
> configured for localhost, external and internal interfaces, and everything
> seems to work fine. snmpwalk's work and everything. However it appears
> that everytime MRTG runs from cron, I lose access to the network
> momentarily from my dsl at home to the external interface on the firewall.
>
> MRTG is running from localhost, and connecting to the snmpd running on
> the external address of the firewall. So... uh... the only thing I have
> come up with is that when MRTG runs, it's taking all the bandwidth in the
> snmp poll on that interface, not allowing me to connect until it's
> finished? Does this make sense?

No not really. Just connect to localhost and read the MIBII

>
> If so, is there a way to connect to snmpd on localhost, and have it
> gather information for another interface?
>
> Eric

Yes, normally it can. I use MRTG to collect the traffic from about 40 cisco
routers/switches.
And don't know if it works the same for a pc. But i suspect it does.

Try to run "snmpwalk 127.0.0.1 [RO communityname] interfaces" and you should
get a list like this with all the interfaces of youre box.

example:
interfaces.ifNumber.0 = 4
interfaces.ifTable.ifEntry.ifIndex.1 = 1
interfaces.ifTable.ifEntry.ifIndex.2 = 2
interfaces.ifTable.ifEntry.ifIndex.3 = 3
interfaces.ifTable.ifEntry.ifIndex.4 = 4

Hopes this helps,
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Mischa
"The only constant thing in live is change"
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