Adding Juniper EX3400 Switch; SNMP fails

[sawdusty]

I'm adding another Juniper EX3400 switch to our network and attempting to get it on NagiosXI but running into some issues. This is a switch that is daisy chained off another EX3400 switch that I added months ago. The existing switch is 192.168.66.12/27, the new switch is 192.168.66.13/27 and they're connected via a 40G QSFP+ port. I can ssh to the switch and when I run the network switch/router host wizard (as I have for all other network devices on our network) I get a message that the host is down, the ip address doesn't exist or that snmp is not working. During my troubleshooting of this problem, I can see flows going through the firewall show send and receive udp/161 traffic from my Nagios server to the switch ip address. I also ran' monitor traffic interface' command and can see the snmp traffic coming in. I can ping the switch from the nagios server, but for some reason the snmp isn't working. Again, the snmp v3 config comes from the same template that I use on everyone of our switches and have not had any issues. I've tried to delete the snmp config from the switch and re-add it but I get the same results. I've confirmed both switches are running the same version of JUNOS software. I'm at a loss as to why this device cannot be monitored.

[sgardil]

I'm adding another Juniper EX3400 switch to our network and attempting to get it on NagiosXI but running into some issues. This is a switch that is daisy chained off another EX3400 switch that I added months ago. The existing switch is 192.168.66.12/27, the new switch is 192.168.66.13/27 and they're connected via a 40G QSFP+ port. I can ssh to the switch and when I run the network switch/router host wizard (as I have for all other network devices on our network) I get a message that the host is down, the ip address doesn't exist or that snmp is not working. During my troubleshooting of this problem, I can see flows going through the firewall show send and receive udp/161 traffic from my Nagios server to the switch ip address. I also ran' monitor traffic interface' command and can see the snmp traffic coming in. I can ping the switch from the nagios server, but for some reason the snmp isn't working. Again, the snmp v3 config comes from the same template that I use on everyone of our switches and have not had any issues. I've tried to delete the snmp config from the switch and re-add it but I get the same results. I've confirmed both switches are running the same version of JUNOS software. I'm at a loss as to why this device cannot be monitored.

Hey @sawdusty

That is a weird one. Could you check for any logs that are on the switch that are relating to snmp? I did some looking up and apparently if the snmp engine times aren't aligned then it can cause authentication issues so that may be something to look into.

[sawdusty]

The only thing I saw related to snmp in the switch logs was an authentication failure. I've used the same template for about a year so I'm not sure how there could be an authentication issue. I rebooted the switch, removed snmp, committed config and then re-added my snmp template and committed again. That seemed to fix it. My guess is the reboot fixed it. Thankfully we hadn't started running anything through that switch yet. This can be marked resolved.

[sgardil]

The only thing I saw related to snmp in the switch logs was an authentication failure. I've used the same template for about a year so I'm not sure how there could be an authentication issue. I rebooted the switch, removed snmp, committed config and then re-added my snmp template and committed again. That seemed to fix it. My guess is the reboot fixed it. Thankfully we hadn't started running anything through that switch yet. This can be marked resolved.

Awesome. glad this was able to get this resolved without more in-depth troubleshooting. That does sound like it possibly could of been a engine timing mismatch between the switches from what I was reading.

[danielmese76]

Got it, thanks for share

[sellan]

I'm adding another Juniper EX3400 switch to our network and attempting to get it on NagiosXI but running into some issues. This is a switch that is daisy chained off another EX3400 switch that I added months ago. Poor Bunny The existing switch is 192.168.66.12/27, the new switch is 192.168.66.13/27 and they're connected via a 40G QSFP+ port. I can ssh to the switch and when I run the network switch/router host wizard (as I have for all other network devices on our network) I get a message that the host is down, the ip address doesn't exist or that snmp is not working. During my troubleshooting of this problem, I can see flows going through the firewall show send and receive udp/161 traffic from my Nagios server to the switch ip address. I also ran' monitor traffic interface' command and can see the snmp traffic coming in. I can ping the switch from the nagios server, but for some reason the snmp isn't working. Again, the snmp v3 config comes from the same template that I use on everyone of our switches and have not had any issues. I've tried to delete the snmp config from the switch and re-add it but I get the same results. I've confirmed both switches are running the same version of JUNOS software. I'm at a loss as to why this device cannot be monitored.

This sounds like a low-level SNMP config issue — likely related to SNMPv3 authentication or interface binding. Since SNMP traffic is reaching the switch, and the same template works elsewhere, I’d zero in on the following:

Verify SNMPv3 user credentials & encryption methods match what Nagios is sending

Ensure SNMP is bound to the right interfaces

Test with SNMPv2 for comparison

[selaopera]

I'm adding another Juniper EX3400 switch to our network and attempting to get it on NagiosXI but running into some issues. This is a switch that is daisy chained off another EX3400 switch that I added months ago. Melon Playground The existing switch is 192.168.66.12/27, the new switch is 192.168.66.13/27 and they're connected via a 40G QSFP+ port. I can ssh to the switch and when I run the network switch/router host wizard (as I have for all other network devices on our network) I get a message that the host is down, the ip address doesn't exist or that snmp is not working. During my troubleshooting of this problem, I can see flows going through the firewall show send and receive udp/161 traffic from my Nagios server to the switch ip address. I also ran' monitor traffic interface' command and can see the snmp traffic coming in. I can ping the switch from the nagios server, but for some reason the snmp isn't working. Again, the snmp v3 config comes from the same template that I use on everyone of our switches and have not had any issues. I've tried to delete the snmp config from the switch and re-add it but I get the same results. I've confirmed both switches are running the same version of JUNOS software. I'm at a loss as to why this device cannot be monitored.

It’s most likely a SNMPv3 engine ID conflict or view/authorization misconfiguration despite using a template. Try testing with snmpwalk, verify the engine ID, and test SNMPv2 to confirm the switch responds.

Let me know if you’d like a checklist or Junos config template for SNMPv3!