Channel for SNMP

[saran_chn]

Can some one explain on what channel SNMP manager tries to communicate the SNMP agent, is it on UDP (161).

Many Thanks,

Saran.

[Joe Clarke]

It's not a channel, but the standard UDP port for SNMP is 161.

[saran_chn]

Thanks but i want to know what happen behind the scenes. Communication between NMS server and SNMP agent.

1. Will the communication channel is always establised.

2. Will the polling intervel is 30 by default from NMS server.

Please explain.

Thanks in advance,

Saran.

[Joe Clarke]

The term channel does not apply. The manager will send an SNMP request to the agent using a UDP (connectionless) socket. The manager will most likely choose a random, high UDP port as the source port for this session. The agent will process the request, then send back a reply to the manager. The agent's packet will have a source port of udp/161, and use the manager's source port as the destination port.

A default polling interval of 30 seconds is typically fine, but it may cause CPU spikes on your device. If so, you should consider lowering it. Applications such as MRTG typically use a five minute polling interval.

[saran_chn]

Thanks jclarke,

Let me explain our setup. We are using Whats up has NMS and its trying to poll all the devices. When i gave show log i could see some logs for the specific component on destination port 23. Please go through the conf and explain.

access-list 100 permit ip 10.72.22.0 0.0.0.255 any log

line vty 0 4

access-class 100 in

transport input telnet

transport output telnet

Switch# sh log

Jan 15 01:06:07.953 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(2315) -> 0.0.0.0(23), 1 packet

Jan 15 01:06:28.899 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(4935) -> 0.0.0.0(23), 1 packet

Jan 15 01:07:23.291 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(3709) -> 0.0.0.0(23), 1 packet

Jan 15 01:07:28.912 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(2275) -> 0.0.0.0(23), 1 packet

Jan 15 01:08:38.521 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(1126) -> 0.0.0.0(23), 1 packet

Jan 15 01:09:28.937 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(3640) -> 0.0.0.0(23), 1 packet

Jan 15 01:09:52.769 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(2398) -> 0.0.0.0(23), 1 packet

Jan 15 01:10:28.949 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(1032) -> 0.0.0.0(23), 1 packet

Jan 15 01:11:08.753 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(3765) -> 0.0.0.0(23), 1 packet

Jan 15 01:11:28.962 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(2315) -> 0.0.0.0(23), 1 packet

Jan 15 01:12:21.810 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(1192) -> 0.0.0.0(23), 1 packet

Jan 15 01:12:28.974 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(3709) -> 0.0.0.0(23), 1 packet

Jan 15 01:13:34.792 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(2470) -> 0.0.0.0(23), 1 packet

Jan 15 01:14:28.999 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(1126) -> 0.0.0.0(23), 1 packet

Jan 15 01:14:51.279 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(3815) -> 0.0.0.0(23), 1 packet

Jan 15 01:15:29.012 GMT: %SEC-6-IPACCESSLOGP: list 100 permitted tcp 10.72.22.4(2398) -> 0.0.0.0(23), 1 packet

Many Thanks,

Saran

[Joe Clarke]

It looks like Whats Up is testing to see if telnet is reachable on this device. This has nothing to do with SNMP.