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NLB stops responding on one IP


Hi everyone,

We've seen this happen a couple of times now. I was wondering if anyone has insights on why this happens, and/or what we can do to prevent or fix it.

Basically, One of the IPs in the network loadbalancer stops responding. We check to make sure the IPs didn't change in DNS or there was another DNS caching issue. I can see no errors or warnings in the target group settings or NLB settings....

$ dig

; <<>> DiG 9.11.3-1ubuntu1.13-Ubuntu <<>>
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50240
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 4, ADDITIONAL: 1
;; WARNING: recursion requested but not available

; EDNS: version: 0, flags:; udp: 4096
; IN A


But, is not responding while does:

$ telnet 22
telnet: Unable to connect to remote host: Connection timed out

$ telnet 22
Connected to
Escape character is '^]'.

Edited by: dh42 on Feb 15, 2021 9:36 AM

Edited by: dh42 on Feb 15, 2021 12:08 PM

asked 2 years ago105 views
2 Answers
Accepted Answer


As you are not able to connect to one of the NLB IP for this NLB, I would request you check that there should be backend target present in the same AZ as of this NLB node then only the connection will be successful.
If you only have one target then make sure that NLB attribute cross-zone is enable for this NLB, so that both node can connect to the same target. If there is target present for the NLB node than only we can connect to that NLB node.

[] Network Load Balancers - Availability Zones -

"After you enable an Availability Zone, the load balancer starts routing requests to the registered targets in that Availability Zone. Your load balancer is most effective if you ensure that each enabled Availability Zone has at least one registered target."


answered 2 years ago

Thanks. For this particular scenario, we have 1 target behind the NLB, but the NLB is provisioned to multiple AZs. Enabling the cross-zone feature on the NLB allows this to work again.

answered a year ago

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