T0 gateway displays a status of "unknown" in NSX UI with error message "FRR config failed:: ROUTING_CONFIG_ERROR (-1)"

Products

• VMware NSX

Issue/Introduction

• T0 is configured in Active/Standby
• Multicast was recently disabled on the T0 
  • Networking > Tier-0 Gateway > [T0] > Multicast > Multicast on/off
• New routing configuration is not pushed to the Edge
• Traffic traversing the Active Edge is affected
• Edge logs show the following error

/var/log/syslog

[TIMESTAMP] <Edge-Node-Name> NSX 3631 SYSTEM [nsx@6876 comp="nsx-edge" subcomp="frr-config" username="frr" level="ERROR"] "Exception while generating FRR Config: ['Traceback (most recent call last):\n', ' File "/opt/vmware/nsx-edge/bin/frr.py", line 536, in apply_config_to_frr\n if generate_frrcfg_txt_from_pb(routing_cfg_msg):\n', ' File "/opt/vmware/nsx-edge/bin/frr.py", line 406, in generate_frrcfg_txt_from_pb\n pim.mcast_cfg(frr_cfg)\n', ' File "/opt/vmware/nsx-edge/python/com/vmware/nsx/edge/frr/pim.py", line 121, in mcast_cfg\n print_mcast_interfaces(frr_cfg, mcast_config)\n', ' File "/opt/vmware/nsx-edge/python/com/vmware/nsx/edge/frr/pim.py", line 66, in print_mcast_interfaces\n if ((mcast.mcast_role == rcpb.MulticastConfigMsg.MCAST_ACTIVE and \\\n', "UnboundLocalError: local variable 'mcast' referenced before assignment\n"]"

[TIMESTAMP] <Edge-Node-Name> NSX 3631 SYSTEM [nsx@6876 comp="nsx-edge" subcomp="frr-config" username="frr" level="ERROR"] "Error in applying the config to FRR"

• Failover to Standby Edge resolves issue

Environment

VMware NSX-T Data Center 3.x

VMware NSX 4.x

Cause

After disabling Multicast on a T0, the Multicast HA role still remains as Active on the Active Edge and Standby on the Standby Edge. On the Active Edge, RCPM continues to push multicast configuration to the Edge which causes the datapath outage.

Resolution

Fixed in NSX-T Data Center 3.2.4

Fixed in NSX 4.2

 

Workaround:

Reboot or place Edges in/out of Maintenance Mode. This will clear the Multicast configuration from the Edges. The issue will not reoccur provided Multicast is not enabled/disabled again.