C:\Users\Administrator>repadmin /showrepl
Repadmin: running command /showrepl against full DC localhost     Default-First-Site-Name\DC1                                       DSA Options: IS_GC                                                Site Options: (none)                                              DSA object GUID: b45f4bfb-05fd-4767-b619-b7d6715081d8             DSA invocationID: b45f4bfb-05fd-4767-b619-b7d6715081d8
==== INBOUND NEIGHBORS ======================================                                                                       CN=Configuration,DC=frankfu,DC=com                                    Default-First-Site-Name\08R2 via RPC                                  DSA object GUID: 753877e7-c79b-4442-95db-6a40bd4d363e             Last attempt @ 2015-12-10 13:59:31 was successful.                                                                          CN=Schema,CN=Configuration,DC=frankfu,DC=com                          Default-First-Site-Name\08R2 via RPC                                  DSA object GUID: 753877e7-c79b-4442-95db-6a40bd4d363e             Last attempt @ 2015-12-10 13:59:31 was successful.                                                                          DC=ForestDnsZones,DC=frankfu,DC=com                                   Default-First-Site-Name\08R2 via RPC                                  DSA object GUID: 753877e7-c79b-4442-95db-6a40bd4d363e             Last attempt @ 2015-12-10 14:03:35 was successful.                                                                          DC=test,DC=frankfu,DC=com                                             Default-First-Site-Name\08R2 via RPC                                  DSA object GUID: 753877e7-c79b-4442-95db-6a40bd4d363e             Last attempt @ 2015-12-10 13:59:31 was successful.                                                                          Source: Default-First-Site-Name\DC2
******* 1 CONSECUTIVE FAILURES since 2015-12-10 13:55:46
Last error: 1722 (0x6ba):                                                     The RPC server is unavailable.                                                                                          Naming Context: DC=ForestDnsZones,DC=frankfu,DC=com               Source: Default-First-Site-Name\DC2
******* WARNING: KCC could not add this REPLICA LINK due to error.                                                                  Naming Context: DC=DomainDnsZones,DC=frankfu,DC=com               Source: Default-First-Site-Name\DC2                               ******* WARNING: KCC could not add this REPLICA LINK due to error.                                                                  Naming Context: CN=Schema,CN=Configuration,DC=frankfu,DC=com      Source: Default-First-Site-Name\DC2
******* WARNING: KCC could not add this REPLICA LINK due to error.                                                                  Naming Context: DC=frankfu,DC=com                                 Source: Default-First-Site-Name\DC2                               ******* WARNING: KCC could not add this REPLICA LINK due to error.                                                                  Naming Context: CN=Configuration,DC=frankfu,DC=com                Source: Default-First-Site-Name\DC2
******* WARNING: KCC could not add this REPLICA LINK due to error.

Possible reason:

1. ensure both servers are on the same subnet 2. check your DNS settings primary DNS should be DC1 3. check your firewall settings

Solution:

Verify the startup value and service status,make sure these are running:

  • the Remote Procedure Call (RPC),
  • Remote Procedure Call (RPC) Locator
  • Kerberos Key Distribution Center.

Reason for this senario: The RPC locator was stop.

Start this service and give both DC a restart.

Reference:
https://support.microsoft.com/en-us/kb/2102154