Transit control plane nodes

[KevinR99]

Is there any reason not to deploy TCN's on Edge stacks?  One TCN in each fabric connected by a SD Transit. 

The edge location is our most cost effective option. 

Kev.

[Torbjørn]

The TCN must be a dedicated node, it cannot be colocated with another role. There's also an upper limit of 4 TCN nodes per SD transit which would limit this design. It is also important that the TCN nodes should all have good connectivity to eachother as they must remain in sync. Topologically your TCN nodes should be placed somewhere that makes sense considering that all border nodes need to establish connections to it. This would be somewhere with very robust connectivity like a central datacenter or hosted at an SP.

[KevinR99]

Thank you.

I may have not explained properly.  The ask is not whether I can co-host the TCN on an edge.  I would be having a dedicated pair of TCNs and I know I can hang them off edge nodes.  I’ve done that in testing. The question is whether there is a compelling reason not to do so given the edges I would use to connect the TCNs to are in DCs. 

[jedolphi]

Hi Kevin, I cant think of a compelling reason to not do this except that it's unusual and might confuse other people that have to manage the network in future. Technically (confused people aside), as long as all BNs have highly available /32 reachability to TC in GRT/underlay then where it connects is not important. Keeping TC out of the forwarding path is preferred, to reduce load on TC. Keep TC user-added configs minimal, to reduce TC complexity. Consider reliable reachabilitiy e.g. if EN has maintenance then TC might become unreachable.

[Torbjørn]

That makes more sense - I misinterpreted your post.

See @jedolphi's response, it's the correct answer to this.