70-294 Concepts: Preferred Bridgehead Server

Here are the design considerations when evaluating a Preferred Bridgehead Server for multi-site deployments of Active Directory:

  • It is best practice to have more than one bridgehead server per site.
  • But if you want to “control” or “manage” site-to-site-replication, you must only choose one preferred bridgehead server.
  • If replication fails in a 3+ site environment, and there are preferred bridgehead servers, change the bridgehead server. Non-fully IP Routable networks may require another (non problem) site to replicate to and the failed PBHS may reside there
  • To avoid single point of failure with PBHS, you need to either have multiple PBHS at each site, or NONE – but this will reduce management.
  • If poor performance on a DC (which is also an app server) make another DC the PBHS, typically the RRAS DC if there is one.
  • Use PBHS for controlling replication traffic, not GC
  • PBHS can be configured for IP and/or SMTP (seperately)
  • Use IP by default, SMTP for unreliable connections
  • SMTP requires a Enterprise Certificate Authority (ECA)

70-294 Concepts: Active Directory Site Links

graduationWhen designing Active Directory Site Links:

  • On non-fully IP routed networks, disable automatic site links, implement a site link bridge
  • A site link is a set of sites which communicate at the same cost, and can be automatically configured to route in a redundant path between sites within a site-link
  • In a fully routed network, you do not need site link bridges unless you wanted to specifically control the flow of replication changes.
  • Controls which sites are connected and at what cost, but does not directly control which servers replicate with one another, this would be the role of a Preferred Bridgehead Server
  • Best Practice to create site links from corporate to branches, little benefit in having a tiered site line corp->branch->branch
  • You cannot create site-links between networks which are not IP routed
  • Site link bridging is used when an IP network is not fully routed; or if replication is not converging properly (used when site’s are 2+ hops away)
  • Site links are for same domain only, and are between IP-routable networks unless you use a ip bridge to connect two non-routable network in the same domain;
  • If two non-routable domains are separated by a site in a different domain, you will need to have a DC setup in that site or you will need a routable network
  • IP Replication for single domain sites; SMTP not available

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