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(ASCEND) UDP port used for SNMP responses



I wonder if anyone can shed any light on a peculair problem I'm
suffering, which I think is down to incorrect behaviour on a Pipeline,
but could equally be down to an incorrect assumption on my behalf.

The following is (modified) output from tcpdump that shows the
problem. The host 'tester' sends a periodic SNMP GetRequest to several
routers to confirm operation, but I see a slight difference in the UDP
port that the response originates from.

 15:24:15.556297 tester.34152 > GRF.snmp: [snmp info snipped] (DF)
 15:24:15.558294 GRF.snmp > tester.34152: [snmp info snipped]

 15:24:14.706030 tester.34150 > pipeline.snmp: [snmp info snipped] (DF)
 15:24:14.703574 pipeline.511 > tester.34150: udp 94

The GRF behaves as I'd expect and responds to me via it's SNMP port
(161), but the Pipeline (a P130 running 5.1Ap4) originates the
response from port 511. In my mind, the SNMP agent should be sourcing
its response from the port it received it on. Because it isn't, the
pipeline firewall software correctly blocks the traffic since it
doesn't look like SNMP anymore.

This looks strikingly familiar to the problem with the RADIUS server
on the MAX sending responses to the RADIUS well known port rather
than the actual client port from which the request came.

Any help or suggestions appreciated,

-- Adam.
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