EDGE HA and DLR

[mansoorahmadkha]

Hey Experts,

Just wanted to know if I have deployed a pair of EDGE appliances (active and standby), will both of them form peer relationship with DLR control VM if running OSPF or its just the active EDGE which will have neighbor relationship with the DLR control VM?

If thats the case and active EDGE goes down, standby EDGE will then proceed to form neighbor and adjacency relationship with DLR control VM?

Thanks in advance

[Sreec]

Only active node establish the peering with upstream/DLR , however forwarding table is in sync between Active and Standby edge

[mansoorahmadkha]

Sreec​ Lets consider OSPF is used as IGP in the NSX environment, below is what I understood from your comment, please confirm.

1. Active EDGE establishes neighbor and adjacency relationship with DLR control VM. Means OSPF state is Full between these two entities after exchanging routes.

2. Standby EDGE does not establish neighbor and adjacency relationship with DLR control VM. What I thought was it develops neighbor relationship but does not actively exchange routes with DLR control VM hence adjacency relationship is not established. I thought the OSPF state between DLR control VM and Standby EDGE is 2-way at this point.

3. When Active EDGE is down, neighbor relationship with DLR control VM is also torn down. At this point, DLR control VM does not have any sort of neighbor relationship with Standby Control VM.

4. At this point, Standby EDGE attempts to establish neighbor relationship with DLR control VM. Means it goes through all OSPF state machine and reaches till Full state after exchanging routes. On the Standby EDGE, was OSPF state in 2-way before the active went down?

Your help is greatly appreciated.

[Sreec]

There is no peering with Standby instances(You will see a empty routing table) , so it will never initiate any packet flow for control plane traffic and concept is same even if you use BGP. When Active fail, standby establish the peering and traffic flow via that. To be more precise standby will have only HA interface configurations and keep live sessions for seamless switch-over and forwarding table will be in sync between the instances .

[mansoorahmadkha]

Just for the sake of more clarity if standby EDGE is not a peer of DLR control VM and active EDGE goes down, it will start neighborship formation process with the DLR control VM. What happens to active traffic during this process since there is no peer relationship on the standby with DLR control VM?

Will it continue to flow as per the forwarding table already known by standby EDGE which is not in active state?

And one more thing, is there any concept of pre-emption between EDGE appliances? If the EDGE appliance which was active before going down comes up again, will it again asume the role of active or will it stay as standby now? Can we configure pre-emption feature between EDGE appliances?

[mansoorahmadkha]

Please respond experts ! ! !

Thanks in advance.

[Sreec]

You should read below threads to understand different scenarios were we can expect downtime

About High Availability ( Check high availability section)

Down time - Edge & Control VM

For your second question : There is no preemption for Edges in NSX-v, it is possible to configure this feature in NSX-T

Preemptive	If the preferred node fails and recovers, it will preempt its peer and become the active node. The peer will change its state to standby. This is the default option.
Non-preemptive	If the preferred node fails and recovers, it will check if its peer is the active node. If so, the preferred node will not preempt its peer and will be the standby node.