Net sight NAC alert - Full Loss of Contact to Switch detected

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Hi there!

We've been implementing a wireless solution with Netsight, Wireless Controllers and a NAC Appliance.

I've been getting this alerts in Netsight:

Full Loss of Contact to Switch detected: 10.0.39.254 due to: Unable to make SNMP contact10.0.255.11 / 10.0.33.254 NAC Lost Contact with Switch Full Loss of Contact to Switch detected: 10.0.33.254 due to: Unable to make SNMP contact
10.0.255.11 / 10.0.3.254 NAC Lost Contact with Switch Full Loss of Contact to Switch detected: 10.0.3.254 due to: Unable to make SNMP contact
10.0.255.11 / 10.0.5.254 NAC Lost Contact with Switch Full Loss of Contact to Switch detected: 10.0.5.254 due to: Unable to make SNMP contact
10.0.255.11 / 10.0.69.254 NAC Lost Contact with Switch Full Loss of Contact to Switch detected: 10.0.69.254 due to: Unable to make SNMP contact
10.0.255.11 / 10.0.9.254 NAC Lost Contact with Switch Full Loss of Contact to Switch detected: 10.0.9.254 due to: Unable to make SNMP contact
10.0.255.11 / 10.0.67.254 NAC Lost Contact with Switch Full Loss of Contact to Switch detected: 10.0.67.254 due to: Unable to make SNMP contact
10.0.255.11 / 10.0.2.254 NAC Lost Contact with Switch Full Loss of Contact to Switch detected: 10.0.2.254 due to: Unable to make SNMP contact
10.0.255.11 / 10.0.6.254 NAC Lost Contact with Switch Full Loss of Contact to Switch detected: 10.0.6.254 due to: Unable to make SNMP contact

What I don't understand is that these IP addresses do not belong to any switch configured. They are configured in a Firewall witch is the default gateway for the wireless client networks.
The firewall is also added to the net sight appliance, but it should only use its management ip address (in-band) 10.0.255.254...

Any ideas?

Best regards,

Tiago Molinos
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Tiago Molinos

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Posted 3 years ago

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Matthew Hum, Principal Engineer, APAC

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The gateway is used to determine MAC-to-IP resolution as a secondary (or tertiary) method. It is trying to pull the ipNet2Media MIB from the gateway, and the management interface (and appropriate credentials) can be configured in the IP Resolution tab of the Appliance Settings.

Is DHCP Snooping set up correctly? are the IPs for end systems resolving correctly?
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Tiago Molinos

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Hi Matthew,

IPs are resolving correctly. I think the problem is with the Firewall how "owns" all the networks gateway IP address. It's not supposed for it to answer SNMP on all it's interfaces, but only on it's management interface. I've configured the NAC appliance with the correct SNMP address and credentials... Just waiting to see if that solved the alert!


Thank you!
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Matthew Hum, Principal Engineer, APAC

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In that case, in the IP Resolution tab, you should enter all the networks you will be using, with their default gateway, and then enter a separate management IP/credentials. You would need to do this for each subnet that clients would be appearing on. I believe thats what you said you did, so you shouldn't have any issues. Please remember to add a NAC appliance as the DHCP helper-address/bootprelay in your firewall config.