I use to have all my DC in the default site that all the domains get put into. DC1, DC2 and DC3. So they are all in same site. Replication was going both directions to and from each server. So each Server. For instance DC1 would go to and from DC2 and DC3, DC2 would go to and from DC1 and DC3, and DC3 would go to and from DC1 and DC2. and Replication was whatever dfault for domains in same zone which I think is 5 minutes. I didn't have any subnets setup or anthing. Last week I changed things around. I changed the default site to First site and created another site called 2nd site. I added subnets to the First Site and I added others to the 2nd site. I then Moved DC3 to the 2nd Site because it was across the WAN and on another subnet. When I move it I check connections again. Here is what the connections show now. DC1 replicates to DC2 and DC3, and replicates only from DC2. Then DC2 replicates to DC1 and from DC1. DC3 replicates to DC2 and from DC1. I not sure why DC3 dropped the from DC2 connection and the replicat to DC1 connection after I moved it to the 2nd site location. I am sure if it did this because its now across the WAN link and it only needs a to come from only one DC and to only one DC. Or Should I go and put the connections back to the way it was when they were when they were all in the same site. So basically add connection DC3 to replicate from from DC2 and the other to replicate to DC1. So that all the DC's replicate to and from each other.
Also The site link going accoss the is set to default when going across from Site to Site. We have a WAN link of 20MB what would be good replication interval.