Control Channel To Transport Node Down Too long due to DNS connectivity issue.

Products

• VMware NSX

Issue/Introduction

• On the NSX Manager, the alarm "Control Channel To Transport Node Down Too Long" is reported.

• Transport Zones show as Degraded.

• var/log/nsx-proxy.log in ESXi host reports timeout errors and DNS resolution errors:
  
  2026-03-03T05:16:13.656Z In(182) nsx-proxy[147588404]: NSX 147588404 - [nsx@6876 comp="nsx-esx" subcomp="nsx-proxy" s2comp="nsx-rpc" tid="147588413" level="INFO"] ConnectionKeeper[448005 ssl://;; communications error to <DNS_server_IP>#53: timed out:1235] attempting connection from timer callback

2026-03-03T05:16:13.658Z Wa(180) nsx-proxy[147588404]: NSX 147588404 - [nsx@6876 comp="nsx-esx" subcomp="nsx-proxy" s2comp="nsx-net" tid="147588413" level="WARNING"] StreamConnection[...] Couldn't resolve 'ssl://...' (error: 1-Host not found (authoritative))

Environment

VMware NSX 4.x

Cause

The ESXi host failed to resolve the NSX Manager FQDN because the DNS server was unreachable during a maintenance window. This prevented the host from identifying the correct IP address for the control plane, causing the ESXi host to be unable to reach its controllers over port 1235.

Resolution

• Ensure DNS server is reachable from the ESXi host on port 53.

• From the Host Transport Node CLI, run the following command to validate connectivity to the manager/controller: nc -zv <NSX_Manager_IP/FQDN> 1235

• From the Host Transport Node CLI, run the following commands to ensure the control channel is established:

  • nsxcli -c get controllers 

  • nsxcli -c get managers

Sample outpout:

[root@esxi-host:~] nsxcli -c get controllers
Wed Jul 21 2021 UTC 08:16:30.127
 Controller IP    Port     SSL         Status       Is Physical Master   Session State  Controller FQDN
 192.#.#.#    1235   enabled     connected             true               up           NA
 192.#.#.#    1235   enabled     connected             false              up           NA
 192.#.#.#    1235   enabled     connected             false              up           NA

[root@esxi-host:~] nsxcli -c get managers
Wed Jul 21 2021 UTC 08:18:43.213
- 192.#.#.#    Connected (NSX-RPC) *
- 192.#.#.#    Connected (NSX-RPC)
- 192.#.#.#    Connected (NSX-RPC)