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What errors report 
<pre><code id="code-20-36978812-1">dcsiag /all</code></pre>
?<br />

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As per your error logs I can firmly say that it is a network / Firewall / Router issue. Please do a tracert to know where exactly you are loosing data packets. However if you run repadmin /replsummary on any DCs it will give you exact errors. Errors like 58, 1722, 1753, 1256. If you get 8524 then think that DNS incorrect configuration (missing records, zones, etc). Make sure that all the DCs connected physically with each other. Also run this command from problematic DC to check RPC port is in listening state or not. Command: &nbsp;telnet replicating patnet DC name 135 (example: telnet DC1 135). Once you execute this command is port is listening state you will see blank screen.
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As per your error logs I can firmly say that it is a network / Firewall / Router issue. Please do a tracert to know where exactly you are loosing data packets. However if you run repadmin /replsummary on any DCs it will give you exact errors. Errors like 58, 1722, 1753, 1256. If you get 8524 then think that DNS incorrect configuration (missing records, zones, etc). Make sure that all the DCs connected physically with each other. Also run this command from problematic DC to check RPC port is in listening state or not. Command:  telnet replicating patnet DC name 135 (example: telnet DC1 135). Once you execute this command is port is listening state you will see blank screen.

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We have 2 site <br />
<br />
eg: site A and site B<br />
<br />
Site A :has 2 servers 1)primary Dc and 2)additional DC<br />
<br />
Site B :has 1 server:Additional DC<br />
<br />
when i run dcdiag on PDC iam geting the following error:&quot;The replication generated an error :&lt;1722&gt; the RPC server is unavailable&quot;<br />
<br />
and when i replicate from ADSS , ntds setting iam getting an error please find the screen shot for the same <br />
<br />
<br />
<a href="https://filedb.experts-exchange.com/incoming/2011/10_w43/512763/error.jpg" target="_blank" class="file-inline" title="RPC ERROR (31 KB)"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><path d="M67.508 468.467c-58.005-58.013-58.016-151.92 0-209.943l225.011-225.04c44.643-44.645 117.279-44.645 161.92 0 44.743 44.749 44.753 117.186 0 161.944l-189.465 189.49c-31.41 31.413-82.518 31.412-113.926.001-31.479-31.482-31.49-82.453 0-113.944L311.51 110.491c4.687-4.687 12.286-4.687 16.972 0l16.967 16.971c4.685 4.686 4.685 12.283 0 16.969L184.983 304.917c-12.724 12.724-12.73 33.328 0 46.058 12.696 12.697 33.356 12.699 46.054-.001l189.465-189.489c25.987-25.989 25.994-68.06.001-94.056-25.931-25.934-68.119-25.932-94.049 0l-225.01 225.039c-39.249 39.252-39.258 102.795-.001 142.057 39.285 39.29 102.885 39.287 142.162-.028A739446.174 739446.174 0 0 1 439.497 238.49c4.686-4.687 12.282-4.684 16.969.004l16.967 16.971c4.685 4.686 4.689 12.279.004 16.965a755654.128 755654.128 0 0 0-195.881 195.996c-58.034 58.092-152.004 58.093-210.048.041z"/></svg>error.jpg</a>
</div>
</div>


error.jpg

We have 2 site 

eg: site A and site B

Site A :has 2 servers 1)primary Dc and 2)additional DC

Site B :has 1 server:Additional DC

when i run dcdiag on PDC iam geting the following error:"The replication generated an error :<1722> the RPC server is unavailable"

and when i replicate from ADSS , ntds setting iam getting an error please find the screen shot for the same 



RPC Server is unavaiable

Windows Server 2008 and Windows Server 2008 R2, based on the Microsoft Vista codebase, is the last 32-bit server operating system released by Microsoft. It has a number of versions, including including Foundation, Standard, Enterprise, Datacenter, Web, HPC Server, Itanium and Storage; new features included server core installation and Hyper-V.

Windows Server 2008

Windows Server 2003 was based on Windows XP and was released in four editions: Web, Standard, Enterprise and Datacenter. It also had derivative versions for clusters, storage and Microsoft’s Small Business Server. Important upgrades included integrating Internet Information Services (IIS), improvements to Active Directory (AD) and Group Policy (GP), and the migration to Automated System Recovery (ASR).

Windows Server 2003

Active Directory (AD) is a Microsoft brand for identity-related capabilities. In the on-premises world, Windows Server AD provides a set of identity capabilities and services, and is hugely popular (88% of Fortune 1000 and 95% of enterprises use AD). This topic includes all things Active Directory including DNS, Group Policy, DFS, troubleshooting, ADFS, and all other topics under the Microsoft AD and identity umbrella.