[mrtg] UDP ports problem

Pablo Abrutzky pablo at overlink.net.ar
Wed Feb 26 18:42:03 MET 2003

I put firewalling rules in my computer, and i have a problem whit
my MRTG.

The problem is whit the UDP ports, because the MRTG send the request from
diferents ports (UDP)..

This is a log (tcpdump)

17:19:17.835728 200.80.40.xx.33508 > 200.80.36.xx.161:  |30|5b|02|01{
SNMPv1 |04|0aC=comunidad |a0|4a{ GetRequest(35) |02|04R=1931794614
|02|01|02|01|30|3c |30|0e|06|0a.|05|00
|30|0e|06|0a.1.3[|snmp]} }  (DF) (ttl 64, id 0, len 121)
17:19:17.877448 200.80.36.xx.161 > 200.80.40.xx.33508:  |30|72|02|01{
SNMPv1 |04|0aC=comunidad |a2|61{ GetResponse(35) |02|04R=1931794614
|02|01|02|01|30|53 |30|13|06|0a.|41|053645644466} }
(ttl 253, id 6545, len 144)

But... the next request:

17:27:44.808630 200.80.40.xx.33510 > 200.80.36.xx.161:  |30|5b|02|01{
SNMPv1 |04|0aC=comunidad |a0|4a{ GetRequest(35) |02|04R=1687433910
|02|01|02|01|30|3c |30|0e|06|0a.|05|00
|30|0e|06|0a.1.3[|snmp]} }  (DF) (ttl 64, id 0, len 121)
17:27:44.851109 200.80.36.xx.161 > 200.80.40.xx.33510:  |30|72|02|01{
SNMPv1 |04|0aC=comunidad |a2|61{ GetResponse(35) |02|04R=1687433910
|02|01|02|01|30|53 |30|13|06|0a.|41|053658067213} }
(ttl 253, id 6547, len 144)

so.. the request is send for the MRTG server, (200.80.40.xx) port 33508
and the response from the client machine (200.80.36.xx) go to the same
port (33508)... but... if i close the UDP ports in this machine i dont
recive the response because the port is diferent any time.

i have a chance to send the request from a specific UDP port, in this case
i close every ports except that.

somebody can help me?

Sorry because my english is very bad.

        Pablo Abrutzky
Analista de Sistemas Informaticos
//Acentos omitidos intencionalmente\\

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