How to identify next-hop edge node for Tier-1/Tier-0 gateways in active-active mode

Products

• VMware NSX
• VMware NSX
• VMware NSX-T Data Center

Issue/Introduction

For Tier-1/Tier-0 gateways in active-active mode 'get logical-router <uuid> forwarding' will show two default routes in the forwarding table with gateway pointing to both edges. This KB provides steps to identify correct edge node used for a particular flow from a specific host.

Environment

VMware NSX-T Data Center
VMware NSX

Resolution

In the below example, there are two default routes in forwarding table of this particular router. This is a Tier-1 router in Active/Active HA mode.

 

esx.example.local> get logical-router 2214affb-2693-4583-9d85-bd5fda6d73eb forwarding

Wed May 22 2024 UTC 08:02:12.113

                                       Logical Routers Forwarding Table

--------------------------------------------------------------------------------------------------------------

Flags Legend: [U: Up], [G: Gateway], [C: Connected], [I: Interface]

[H: Host], [R: Reject], [B: Blackhole], [F: Soft Flush], [E: ECMP]

 

                   Network                               Gateway                Type               Interface UUID

==============================================================================================================

0.0.0.0/0                                              169.x.x.x              UGE     348953c8-120e-43c9-be05-88edcf7b83a6

0.0.0.0/0                                              169.x.x.x              UGE     348953c8-120e-43c9-be05-88edcf7b83a6

 

For this particular flow from source 172.x.x.x to destination 8.8.8.88, run the following command on source host (where VM 172.x.x.x resides) to identify correct gateway.

 

[root@esx:~] net-vdr -R -o resolve -e 172.x.x.x -i 8.8.8.88 2214affb-2693-4583-9d85-bd5fda6d73eb

 

DR 2214affb-2693-4583-9d85-bd5fda6d73eb Route Table

Legend: [U: Up], [G: Gateway], [C: Connected], [I: Interface]

Legend: [H: Host], [B: Blackhole], [F: Soft Flush] [!: Reject] [E: ECMP]

 

Destination      GenMask          Gateway          Flags    Ref Origin   UpTime     HitCount   Lif UUID

-----------      -------          -------          -----    --- ------   ------     --------   ---------

0.0.0.0          0.0.0.0          169.254.0.2      UGE      3   618619     113224     348953c8-120e-43c9-be05-88edcf7b83a6

[root@esx:~]

Additional Information

Return path for traffic originating from outside NSX and entering NSX edge will be determined by uplink ToR switch.