[mrtg] Re: no SNMP Response

[Alex van den Bogaerdt]

yuriy wrote:

> I debugged snmp in this box, but no activity ...
> So, - firewall is most likely problem?
> But I don't have enough experience with firewalling, so, - what basic
> parameters (port, protocol etc)
> should I ask them to check?

SNMP works on udp port 161.

Request:
   Source:      <your computer> port <random port above 1023>
   Destination: <other box> port 161

Reply:
   Source:      <other box> port 161
   Destination: <your computer> port <same random port above 1023>

Firewalling problems are best checked, if possible, by sniffing packets
on both sides of the firewall.  If you see packets on both sides, the
firewall is not the problem.  If the firewall *is* blocking your packets,
the packets will be visible on the outside and not on the inside.

Sometimes a firewall is letting the request through but is blocking the
reply; if this would be the case you would have seen packets on the box
you're monitoring.

HTH
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