I have 5 DCs in a WAN environment. Yesterday my Root DC stopped replying to one of those DCs. Now the servers do send/receive information but the Root doesn't replicate with the one DC anymore. The DC that cannot replicate states that the Root DC's RPC isn't available. All of the other DC's work properly and do not report any problems replicating.
I have tried removing and re-adding the site in sites and services, I have tried having that server added to a different site to see if it could replicate with any other of the DC's but that gives another error.
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