SDWAN controller connection questions

[TechnStuff]

Can someone help me with these questions?

Assumptions:
max-control connections set to default (2)
There are more than 2 vSmarts and vBonds in the environment.

1. How does an edge determine which vBond to connect to? Is it based on latency, or do edges cycle through all configured vBond IPs, starting with the lowest IP?
2. When an edge connects to a vBond, does the vBond provide a list of all known vSmarts, or is the list limited to a specific number?
3. When an edge receives a list of all known vSmarts, what criteria does it use to select a specific vSmart to establish a control connection?
4. If an edge loses connection to an existing vSmart, does it initiate an OMP graceful restart, waiting for the connection to be restored, or does it attempt to establish a connection with another vSmart?
5. Does a vBond attempt to load balance vSmart connections? If it does, how does this process work in an environment with multiple vBonds? Could this potentially result in an uneven number of connections to vSmarts due to communication between vBonds?

[M02@rt37]

Hello @TechnStuff 

1. The process of an edge determining which vBond to connect to is typically based on DNS resolution. The edge uses the domain name associated with the vBond orchestrator, and DNS returns the IP address of an available vBond. It is not typically based on latency or a cycling through configured vBond IPs.

2. When an edge connects to a vBond, the vBond provides the edge with a list of all known vSmarts in the overlay network.

3. The criteria an edge uses to select a specific vSmart from the provided list is based on factors such as load balancing and the available resources on each vSmart. The edge makes an informed decision to distribute control connections across the available vSmarts.

4. If an edge loses connection to an existing vSmart, it does not initiate an OMP (Overlay Management Protocol) graceful restart. Instead, it attempts to establish a connection with another vSmart from the list provided by the vBond.

5. Yes, vBond orchestrators attempt to load balance control connections to vSmarts. In an environment with multiple vBonds, they coordinate to distribute the load across the available vSmarts. This load balancing process helps prevent uneven distribution of connections and ensures efficient utilization of resources. Communication between vBonds is part of the coordination to achieve load balancing.

[TechnStuff]

MO2@rt37 Thanks for your reply

1. When using a host entry that maps to multiple vBonds, how does the edge handle the connection? Does it connect to the first vBond in the list?

3. Is it possible to see what vSMart information is returned to an edge by a vBond?
 
4. That was my understanding too but I saw different behavior in my setup, where when an edge lost connection to a vSmart, it did not try to attempt connection to alternate vSmart.

5. For vBonds, my understating is that they don't setup any control connections between them (unlike vSmarts that do). How do they coordinate?

I am talking about on-prem controller setup here.

[Kanan Huseynli · Accepted solution]

Hi,

1) sequentially until device is successfully creates control connection to vBond

...and the router tries each address sequentially until it forms a successful connection. 

2) vBond always send all controllers list

3) If affinity is configured then device connects to controllers sequentially based on affinity list. If not, then internal load balancing is done by router

When the number of Cisco SD-WAN Controllers in a domain is greater than the maximum number of controllers that a domain's Cisco IOS XE Catalyst SD-WAN devices are allowed to connect to, the Cisco Catalyst SD-WAN software load-balances the connections among the available Cisco SD-WAN Controllers. 

4) No graceful restart, it is not mentioned in HA guides, device tries to connect next available (from affinity group or just from the list when no explicit affinity group exists till max allowed number)

5) I don't think that vBond helps somehow in vSmart connections distribution, I would like to see - read in doc.

[M02@rt37]

@TechnStuff 

1. When a host entry maps to multiple vBonds, the edge typically selects one vBond based on DNS resolution. It doesn't necessarily connect to the first vBond in the list; DNS resolution provides an IP address, and the edge connects to that vBond.

3. To view the vSmart information returned to an edge by a vBond, you might need to check debug logs or specific commands on the edge device. 

4. The behavior you observed where an edge doesn't attempt to connect to an alternate vSmart upon losing connection might be influenced by specific conditions or configurations. It's also possible that the edge has a specific order or priority for vSmarts that it follows.

5. In an on-prem controller setup, vBonds indeed do not set up control connections among themselves. They coordinate through the control connections with vSmarts. The coordination involves sharing information about available vSmarts and helping in load balancing control connections. This coordination is part of the orchestration provided by the vBond orchestrator.

[Kanan Huseynli]

Could you provide resource- document- proof about " helping in load balancing control connections"?