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site links and site link bridges

    Question

  • Hi all,

    I have been trying to find documentation to answer a pair of doubts I have about site transport, but could not find answer to them.

    This are the questions:

    If a create a site link and after that, connections are automatically generated, there is a direct relation between site links and those connections, isn't it? is there any way to check what site link has been responsable to generate each connection?

    About site link bridges, when I create a site link bridge, are there new connections coming from that brigde or connection are just coming from site links? if the second one, what are the result to create a site link brigde?

    Thank you very much

    David

    Monday, November 06, 2017 11:35 AM

Answers

  • A site link bridge designates a section of your network that is fully IP routed. It means that theoretically
    connections can be built not only along site links, but also between any two sites in the site link bridge if the topology generator finds it better. In practice that happens rarely, although I can imagine that in a complicated network with many DCs the topology can be built not only along the site links.

    For example if you have links A-B and A-C and bridge all three in a link bridge the topology generator can build connection from B to C directly and it will be perfectly valid.

    As I said, it is only for very complicated topologies, where your human brain will probably be unable to calculate the best route. In most situation connections will be along site links with lowest costs.

    Tuesday, November 07, 2017 6:17 PM
  • Hi,

    >> Now I have added two link bridge, one holding links 1-3 and 3-4 and another one holding 1-2 and 1-3. Sincé I have done this, no new connections have been created.
    Have you configured the bridge-head server for the sites? If not, this may be a normal behavior. In this case, I'd like to explain the difference between two terms: KCC and ISTG:
    KCC: KCC is responsible for generating site replication topologies between domain controllers and creating connections objects. It works on the site level.
    ISTG: In case of site level, there will be a bridge-head server to manage site to site replication. ISTG (Inter-Site Topology Generator) is responsible for creating connection objects in bridge-head servers.

    You may refer to the following links for details:
    Creating a Site Link Bridge Design
    https://technet.microsoft.com/en-us/library/cc753638(v=ws.10).aspx
    Determine the ISTG Role Owner for a Site
    https://technet.microsoft.com/en-us/library/cc794776(v=ws.10).aspx

    If you need further help, please feel free to let us know.
     
    Best Regards,
    Albert Ling

    Please remember to mark the replies as an answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com

    Wednesday, November 08, 2017 8:51 AM
  • Hi,

    Just checking in to see if the information provided was helpful.

    Please let us know if you would like further assistance.

    Best Regards,
    Albert Ling

    Please remember to mark the replies as an answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com

    Friday, November 10, 2017 4:59 AM

All replies

  • It is the entire topology that is used when connections are generated, not a single site link.

    By default all site links are bridged, and you do not need to create site link bridges.

    You only need to do it if you disable "Bridge all site links" setting. You may want to do it if you do not have full IP connectivity between all DCs in your network. For example I have done it in one of the projects where site DCs could only connect to their neighbour sites DCs, not any DC in the domain. 

    Tuesday, November 07, 2017 12:35 AM
  • Hi David,

    Based on my research, I'd like to explain that the connections between domain controllers are generated and maintained by KCC, not site links or site link bridges. Within a site, each KCC generates its own connections. For replication between sites, a single KCC per site generates all connections between sites. And if the configuration of Active Directory Sites and Services has been changed, the KCC checks the topology every 15 minutes and makes changes as necessary. In addition, you can also delete automatically generated connections and create custom connections.

    For more information, please refer to the following article:
    KCC and Topology Generation
    https://technet.microsoft.com/en-us/library/cc961781.aspx

    If you need further help, please feel free to let us know.

    Best Regards,
    Albert Ling

    Please remember to mark the replies as an answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com

    Tuesday, November 07, 2017 6:38 AM
  • Hello Albert and I.A

    Thank you both for your answers. But even with these I have a few questions

    I have a lab, with five sites. I have deactivated "bridge all site links" becasue I am trying to get an idea of the diference between site link and site link brigde. I have created a site link between sites 1-2, 1-3, 1-5 and 3-4 so I get and idea of how links are created. connections have been created according to this links, and they follow it perfectly.

    Now I have added two link bridge, one holding links 1-3 and 3-4 and another one holding 1-2 and 1-3. Sincé I have done this, no new connections have been created. I do not get an idea of what link sites are for. And additionally, if a site link bridge should hold site links with at least a common site, How is it that I can create site links brigde without common sites in it?

    Thank you

    Tuesday, November 07, 2017 9:51 AM
  • A site link bridge designates a section of your network that is fully IP routed. It means that theoretically
    connections can be built not only along site links, but also between any two sites in the site link bridge if the topology generator finds it better. In practice that happens rarely, although I can imagine that in a complicated network with many DCs the topology can be built not only along the site links.

    For example if you have links A-B and A-C and bridge all three in a link bridge the topology generator can build connection from B to C directly and it will be perfectly valid.

    As I said, it is only for very complicated topologies, where your human brain will probably be unable to calculate the best route. In most situation connections will be along site links with lowest costs.

    Tuesday, November 07, 2017 6:17 PM
  • Hi,

    >> Now I have added two link bridge, one holding links 1-3 and 3-4 and another one holding 1-2 and 1-3. Sincé I have done this, no new connections have been created.
    Have you configured the bridge-head server for the sites? If not, this may be a normal behavior. In this case, I'd like to explain the difference between two terms: KCC and ISTG:
    KCC: KCC is responsible for generating site replication topologies between domain controllers and creating connections objects. It works on the site level.
    ISTG: In case of site level, there will be a bridge-head server to manage site to site replication. ISTG (Inter-Site Topology Generator) is responsible for creating connection objects in bridge-head servers.

    You may refer to the following links for details:
    Creating a Site Link Bridge Design
    https://technet.microsoft.com/en-us/library/cc753638(v=ws.10).aspx
    Determine the ISTG Role Owner for a Site
    https://technet.microsoft.com/en-us/library/cc794776(v=ws.10).aspx

    If you need further help, please feel free to let us know.
     
    Best Regards,
    Albert Ling

    Please remember to mark the replies as an answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com

    Wednesday, November 08, 2017 8:51 AM
  • Hi,

    Just checking in to see if the information provided was helpful.

    Please let us know if you would like further assistance.

    Best Regards,
    Albert Ling

    Please remember to mark the replies as an answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com

    Friday, November 10, 2017 4:59 AM
  • Hi both,

    Thank you very much for your answers.

    I haven't designated any brigdehead, as in this lab most of sites are only running one DC. But I will extend now my lab to test also with brigdehead DCs.

    Now it is much clearer for me what site link and site link bridges are.

    Thank you very much

    Best regards,

    David



    Friday, November 10, 2017 8:21 AM