I will try and keep this simple. We have 6 sites in our fully routed network.

Site 1 - 4 DCs - 1Gbps connection

Site 2 - 1 DC - 1Gbps connection

Site 3 - 1 DC - 50Mbps connection

Site 4 - 1 DC - 100Mbps connection

Site 5 - 1 DC - 100Mpbs connection

Site 6 - 1 DC - 20Mbps connection

All of these sites were in the same site link and none of the subnets were mapped to sites. I have since then, mapped all of our sites without dcs (These are offices with 1 or 2 people) to the closets DC.

I linked site 1 and 2 with the 1Gbps connection together. I then linked site 3 and 4 to site 1, and , linked site 2 to site 5 and 6.

What I am wondering, is if the circuit @ site 1 goes down, will site 3 and 4 be able to replicate? Same for Site 2. How this is configured now, is it best practice? I have no more than 2 sites in a site link. Should I link site 6 and 5 to site 1 with a higher cost?

Any help will be greatly appreciated! I started looking into this when I noticed how long it was taking password resets to replicate. Just by doing this alone has fixed the problem. I just want to make sure this correctly configured. Please be critical and give me any tips to make this better!

Picture for Reference:

Site Link Diagram - Each colored link represents an individual site link between 2 sites only.

Detailed settings added

  • Site 1 and 2 are in a site link together with no other sites. I made additional site links, such as Site 1 to site 3 and site 1 to 4. – mild0d2 Feb 17 '19 at 21:20
  • Can you provide a diagram or drawing? – joeqwerty Feb 17 '19 at 21:27
  • I just added a picture for reference to the original post. – mild0d2 Feb 17 '19 at 21:34
  • if the circuit @ site 1 goes down, will site 3 and 4 be able to replicate? You should specify if you have a fully routed network where all sites can communicate with each other, and if the Bridge All Site Links setting is enabled (enabled is the default). – Greg Askew Feb 17 '19 at 21:54
  • IF BASL is enabled (which it is by default), and if Site 1 goes offline then all other sites will continue to replicate with each other. If BASL is disabled and Site 1 goes offline then Sites 3 and 4 will be isolated. – joeqwerty Feb 17 '19 at 22:22

Yes, best-practice is to have only 2 sites per link. Your site links should be aligned to your network topology. Is the network routed between all sites?

If they are, then you can leave Bridge All Site Links enabled and the DCs will replicate even if a site is missing. However, it's really useful to do some traceroute tests (different times of the day) and so on to check latency between your sites.

If there are instances of sites where there is a significant difference in the traceroute results for any of the potential secondary sites, this is where you want to put in higher-cost links between the worse-performing ones.

In a fully-routed topology, higher-cost site links are really more about reducing replication and authentication latency in normal operations. They're not critical to operations or resiliency when a site goes down. So it's only worth putting the higher-cost links in if there is going to be a significant difference to performance if a site goes missing.

If the network topology isn't fully-routed, or you have firewalls between various segments, then you can disable Bridge All Site Links and set up Site Link Bridges manually to reflect the topology. Then work out link costs for primary/secondary routes.

  • Thank you!, exactly what I was thinking but wanted a second opinion. – mild0d2 Feb 18 '19 at 1:12
  • @mild0d2: FYI by default, if a computer cannot locate a DC in its own site, it may authenticate with any DC. A computer in Site 6 may authenticate with a DC in Site 4, which may not be desired. Policy setting: System\Net Logon\DC Locator DNS Records > 'Try Next Closest Site' enables the computer to attempt to locate a DC in the nearest site based on the site link cost if a DC in same the site is not found. – Greg Askew Feb 18 '19 at 15:32
  • @mild0d2: Also, if Site 1 and Site 2 have fast low-latency connectivity, you should consider enabling change notification. blogs.technet.microsoft.com/qzaidi/2010/09/23/… – Greg Askew Feb 18 '19 at 15:32

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