SNMPWALK - TimeOut: No Response from address

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SNMPWALK - TimeOut: No Response from address

Postby hbackus » Sat Jun 30, 2018 5:41 pm

I am running Nagios Core 4.2.2
snmpwalk on the localhost returns information on MIB.
snmpwalk run against a switch with snmp turned on returns a timeout message.
All thing being equal shouldn't I get some response besides timeout?

# snmpwalk -v 1 -c public localhost
SNMPv2-MIB::sysDescr.0 = STRING: Linux nagios.mynetwork.local 2.6.32-642.el6.x86_64
(the rest remove to save space)

# snmpwalk -v 1 -c public 10.30.25.11
Timeout: No Response from 10.30.25.11

# yum list installed
net-snmp.x86_64 1:5.5-60.el6 @base
net-snmp-libs.x86_64 1:5.5-60.el6 @base
net-snmp-perl.x86_64 1:5.5-60.el6 @base
net-snmp-utils.x86_64 1:5.5-60.el6 @base
(the rest remove to save space)

Thanks for any guidance

~hbackus
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Re: SNMPWALK - TimeOut: No Response from address

Postby cdienger » Mon Jul 02, 2018 11:24 am

Yes, you should be getting a response assuming everything is equal.

Is the device only doing v1? 2c is pretty common and I'd try running the command with the "-v 2c" option as well.

There could also be a firewall between the devices preventing communication over UDP port 161. Can you verify on the end device if the SNMP traffic is even making it over?
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Re: SNMPWALK - TimeOut: No Response from address

Postby hbackus » Mon Jul 02, 2018 3:07 pm

Thanks for the kind response. Here is what I have uncovered so far.

It is obvious at this point that I do not know all the ins and outs on setting up SNMP.
Telling snmpwalk to use version 1 or version 2c does not change the message from the Nagios server running snmpwalk. "Timeout: No response from (ip_address)".

There is no firewall between the systems but they are on separate LAN segments.

I setup a packet capture on a span port for the server and I see the SNMP “get-next-request” made by the Nagios snmpwalk command.
I also see a return frame with "Error-status (no-error)" in the "SNMP data section" of the capture.

So if the request is going out and the reply is coming back, what would I have miss-configured or failed to configure for SNMP at the Nagios server that would cause “Timeout: No response from (ip_address)” to occurr?

:?
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Re: SNMPWALK - TimeOut: No Response from address

Postby cdienger » Tue Jul 03, 2018 10:47 am

I would take a closer look at the resposne. Try the following on XI's command like to get a packet capture:

yum -y install tcpdump
tcpdump -s 0 -i any host 10.30.25.11 -w output.pcap

Let this run just long enough to run the snmpwalk command and then use CTRL+C to stop it. output.pcap can be viewed with wireshark and you can also PM it to me if you'd like a second pair of eyes to take a look.
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Re: SNMPWALK - TimeOut: No Response from address

Postby cdienger » Fri Jul 06, 2018 9:14 am

Thanks for the tcpdump. The behavior it shows is strange.

First XI sends a snmpwalk request from source port 53373 to destination port 161 - so far so good

The destination appears to react to the request but not in an expected way and one that would produce the error message. Instead of sending a response to XI on port 53373, it sends XI a SNMP Trap on port 162 - This is the problem. In order for the SNMPWALK to work the destination should respond with a SNMP get-response message on port 53373 and not a snmpV2-trap message on port 162.'

You can see valid SNMP traffic with the example at https://wiki.wireshark.org/SampleCaptures#SNMP.
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Re: SNMPWALK - TimeOut: No Response from address

Postby hbackus » Fri Jul 06, 2018 11:17 am

OK, thanks.

I will look into it and update when I can.
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Re: SNMPWALK - TimeOut: No Response from address

Postby cdienger » Fri Jul 06, 2018 12:22 pm

Sounds good. We'll be here :)
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Re: SNMPWALK - TimeOut: No Response from address

Postby hbackus » Fri Jul 06, 2018 3:27 pm

If you like weird, I may have just the thing for you.

I made no changes to the Nagios Core server.
I went to the switch I was running snmpwalk against and added a config line that said the snmp client was the Nagios server.
No change, the snmpwalk still timed out with no response as the error message.
I removed all the snmp configuration lines in the switch and then added them back in (in reverse order).
The configuration on the switch still showed the entries in the same order as before.
I ran snmpwalk and got a response.

SNMPv2-MIB::sysDescr.0 = STRING: Brocade Communications Systems, Inc.
SNMPv2-MIB::sysObjectID.0 = OID: SNMPv2-SMI::enterprises.1991.1.3.48.5.1
DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (1829683300) 211 days, 18:27:13.00
[lines removed for brevity]
SNMPv2-SMI::mib-2.192.1.1.1.0 = Gauge32: 50
SNMPv2-SMI::mib-2.192.1.1.2.0 = INTEGER: 2

Not sure if I needed all the lines in the configuration of the switch or not or if just removing them and adding them back “bumped” snmp enough that it started working.
I have about 15 more switch stacks to try this on, but I am leaving this one as is.

Thanks for your time and efforts. You can lock this thread down if you like.
:)
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Re: SNMPWALK - TimeOut: No Response from address

Postby cdienger » Fri Jul 06, 2018 4:08 pm

I'll take weird as long as it's resolved :)
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