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intersite replication

    Question

  • hi,

    i want to know more about replication. in particular i want to know about seting moment of replication between sites.

    in 'link and services' there are three places where we configure time,schedule of replication:

    1. DEFAULTIPSITELINK - here we are 'cost' and 'replicate every'

    2. NTDS Site Settings for site - schedule

    3. NTDS Settings for bridgehead server - schedule.

     

    if leave default value 'replicate every' - 180 min - and chage schedule for site - every 15 minutes - which setting is stronger? and what about schedule for bridgehead server? 

     

    thx in advance for any info.

     


    Voytas
    Wednesday, October 13, 2010 3:55 PM

Answers

  • My understanding is that the schedule of the bridgehead server, or more correctly the schedule of the connection that is automatically generated by the bridgehead server of one site to the bridgehead server of another site is based on the 'replicate every' setting of the site link. Not quite correct to say 'the same as' but rather 'is based on' - but yes, they should be the same.

    AD will use the 'intersite topology generator' (ISTG) and the 'knowledge consistency checker' (KCC) (theres two things to google :o)) periodically to ensure that information is sufficiently being replicated, and will regenerate any connections as required. The more important one to change is the 'replicate every' setting of the site link and to ensure that the schedule of the site link reflects what times of the day you want replication to take effect (i.e. every 180 minutes, 24 hours a day?, or maybe every 15 minutes but only during work hours?). KCC and ISTG should automatically update the schedule of the bridgehead server as required.

    I have not done any testing to see how quickly these changes are reflected in the bridgehead servers connections schedule, and as the intersite replication defaults to 180 minutes it may take 3 hours before the faster replication schedule settings to be replicated, you might need to check this out :o) - I've just changed one on a site of mine, I'll let you know how long it takes to replicate

    I believe it is advised that manual settings are not done on the connections between domain controllers, bridgehead or otherwise, but that the 'NTDS Site Settings' (for internal replication of a site) and the "site links" (for between sites) be used to control the schedules, connections etc... and that KCC and ISTG be allowed to do their thing :o). Having said that the option to change the schedule directly on the connection is available as a kind of 'manual override' so if you really want to change it directly I believe that's why it's there! The direct change will override the other settings

    This link is for 2000 but is still applicable I think, it just doesn't seem to include information about the notification process the dc's go through, which might have been a 2003 or 2008 feature... http://technet.microsoft.com/en-us/library/cc961612.aspx "Server and Site Connections". I hope it helps with the explanation.

    Thank you!

    • Marked as answer by Voytass Monday, October 18, 2010 4:58 PM
    Wednesday, October 13, 2010 11:05 PM
  • I wouldn't suggest deleting any connections, as long as they are all automatically generated connections AD should be allowed to maintain them. If, however, you have changed the schedules on the connections manually then it may be that they are 'manually overridden' and won't automatically change - I'm not sure about this I would need to test it. I believe if you delete the connections the KCC and ISTG will automatically recreate them, and 'check replication topology' is a way of forcing it to do just get on with it now rather than the next scheduled time...

    The following technet article says "Active Directory runs the intersite topology generator on one domain controller in a site to consider the cost of intersite connections and to check if any previously available domain controllers are no longer available or if new domain controllers have been added. Then, the Knowledge Consistency Checker (KCC) uses this information to add or remove connection objects as needed for efficient replication. This process does not affect manually created connection objects. Only one domain controller per site assumes the role of the intersite topology generator."

    http://technet.microsoft.com/en-us/library/cc739234(WS.10).aspx

    • Marked as answer by Voytass Monday, October 18, 2010 4:58 PM
    Friday, October 15, 2010 1:06 AM

All replies

  • Hi Voytas

    RE: DEFAULTIPSITELINK "Costs" and "Replicate Every". This is for replication between DIFFERENT sites...

    When you have multiple sites you link togethor the sites with a site link. Here you specify the cost of the site link. If you had say 3 sites A, B an C that were all connected you might have 3 different site links to 'link' them all togethor. We might call the site links, and set their cost, as follows:

    "Link A--> B" - Cost: 100
    "Link B--> C" - Cost: 100
    "Link C--> A" - Cost: 300

    Thus everything is connected. The 'cost' allows AD to decide how best to replicate traffic. In the above example AD would prefer to replicate traffic from Site A to B then B to C for a total cost of 200 rather than replicating directly from C to A at a cost of 300.

    The replicate every and schedule options found in the site link are as follows:

    Replicate every is when the elected bridgehead for the site will poll it's nearest upstream bridgehead server to see if there have been any changes... If you want traffic to be updated quicker then lower this time, I think the lowest is 15 minutes. The schedule in the site link is what times of the day traffic is allowed to replicate over that site link, and the replication will occur at the increments set by the 'replicate every' OR if you where to instigate an forced update with repadmin or other method...

    RE: NTDS Site Settings schedule - this controls replication WITHIN a single site.

    Now by default Domain Controllers in a single site will notify other domain controllers if something has been changed at the replication happens within moments of making a change HOWEVER it might also be possible an error has occured. This schedule is to ensure replication happens, by default, at least once an hour WITHIN a site...

    RE: The schedule on the NTDS Settings of the BridgeHead server I couldn't find 'schedule'. I could find schedule by clicking the NTDS Settings on the left under a bridge head server (or indeed any DC) and on the right hand pane viewing the properties of one of the connections... Is that where you mean?

    These connections between servers, assuming they are automatically generated, get their schedule automatically from either the NTDS Site Settings (if they are domain controllers in a single site) or from the Site Link schedule, if they are bridgehead servers between sites. One site I am viewing at the moment the 'site link replicate every' setting is set to every 180 minutes, and the schedule is 24/7 available, so when i view the automatically generated schedule of the connection it has 'once per hour' ticked every three hours...

    I hope that all makes sense!!!

    To specifically answer your question, if you change the site schedule to 15 minutes it will cause the domain controllers inside the site to talk to each other every 15 minutes to ensure they have the latest and to detect and connectivity issues... if you leave the default 'replicate every' value at 180 minutes this will concern replication between the sites attached to that site link and will leave them communicating once every 3 hours...

    I would leave the schedule for the bridgehead server alone, it is automatically generated... if you want information to replicate more frequently between two sites then edit the 'replicate every' setting for the site link that is linking the two sites (in your case defaultipsitelink).

    Hope that helps!

    • Proposed as answer by Mike Kline Wednesday, October 13, 2010 5:06 PM
    Wednesday, October 13, 2010 4:52 PM
  • Hi,

    thx for explanation.

    ok, i got it.

    as you wrote, bridgehead schedule was for connection not NTDS itself.

    one question - so the replication schedule for bridgehead server is the same as  'replication every' for default site link. but when i change it what is more important? sitelink 'replicate every' or schedule of bridgehead server? or maybe is a sum both?

     


    Voytas
    Wednesday, October 13, 2010 6:04 PM
  • Here is some additional information regarding site link cost if you are interested.

    Determine What is the Appropriate Active Directory Site Link Cost
    http://www.anitkb.com/2010/10/determine-what-is-appropriate-active.html

     


    Visit: anITKB.com, an IT Knowledge Base.
    Wednesday, October 13, 2010 6:05 PM
  • My understanding is that the schedule of the bridgehead server, or more correctly the schedule of the connection that is automatically generated by the bridgehead server of one site to the bridgehead server of another site is based on the 'replicate every' setting of the site link. Not quite correct to say 'the same as' but rather 'is based on' - but yes, they should be the same.

    AD will use the 'intersite topology generator' (ISTG) and the 'knowledge consistency checker' (KCC) (theres two things to google :o)) periodically to ensure that information is sufficiently being replicated, and will regenerate any connections as required. The more important one to change is the 'replicate every' setting of the site link and to ensure that the schedule of the site link reflects what times of the day you want replication to take effect (i.e. every 180 minutes, 24 hours a day?, or maybe every 15 minutes but only during work hours?). KCC and ISTG should automatically update the schedule of the bridgehead server as required.

    I have not done any testing to see how quickly these changes are reflected in the bridgehead servers connections schedule, and as the intersite replication defaults to 180 minutes it may take 3 hours before the faster replication schedule settings to be replicated, you might need to check this out :o) - I've just changed one on a site of mine, I'll let you know how long it takes to replicate

    I believe it is advised that manual settings are not done on the connections between domain controllers, bridgehead or otherwise, but that the 'NTDS Site Settings' (for internal replication of a site) and the "site links" (for between sites) be used to control the schedules, connections etc... and that KCC and ISTG be allowed to do their thing :o). Having said that the option to change the schedule directly on the connection is available as a kind of 'manual override' so if you really want to change it directly I believe that's why it's there! The direct change will override the other settings

    This link is for 2000 but is still applicable I think, it just doesn't seem to include information about the notification process the dc's go through, which might have been a 2003 or 2008 feature... http://technet.microsoft.com/en-us/library/cc961612.aspx "Server and Site Connections". I hope it helps with the explanation.

    Thank you!

    • Marked as answer by Voytass Monday, October 18, 2010 4:58 PM
    Wednesday, October 13, 2010 11:05 PM
  • Just an update on how to force it to update the bridgehead schedule after you change the site link 'replicate every' settings.

    I changed the Site Link 'replicate every' settings to 60 minutes. I think went to the bridge head server and expanded it so I could see 'NTDS Settings' underneath, then right clicked NTDS Settings, chose 'all tasks' then 'check replication topology'. Left it for about 15/20 minutes and came back and checked the schedule on the connection between the bridgehead servers and it was now once an hour every hour.

    I assume if left to it's own devices it would have done this anyway, but thought this was a nifty way to see the result straight away.

    Wednesday, October 13, 2010 11:48 PM
  • thx for your info about that.

     

    i done the same as you wrote. changed sitelink 'replicate every' to 30 min, run 'check replication topology' and after 15/20 min i look at connection schedule and there was not any change. earlier i putted in schedule different replication duration between 8:00 and 20:00 to see if all be changed to 30 min. nothing.

    i think that i should delete connection before 'check replication topology' ?

     

     


    Voytas
    Thursday, October 14, 2010 12:02 PM
  • I wouldn't suggest deleting any connections, as long as they are all automatically generated connections AD should be allowed to maintain them. If, however, you have changed the schedules on the connections manually then it may be that they are 'manually overridden' and won't automatically change - I'm not sure about this I would need to test it. I believe if you delete the connections the KCC and ISTG will automatically recreate them, and 'check replication topology' is a way of forcing it to do just get on with it now rather than the next scheduled time...

    The following technet article says "Active Directory runs the intersite topology generator on one domain controller in a site to consider the cost of intersite connections and to check if any previously available domain controllers are no longer available or if new domain controllers have been added. Then, the Knowledge Consistency Checker (KCC) uses this information to add or remove connection objects as needed for efficient replication. This process does not affect manually created connection objects. Only one domain controller per site assumes the role of the intersite topology generator."

    http://technet.microsoft.com/en-us/library/cc739234(WS.10).aspx

    • Marked as answer by Voytass Monday, October 18, 2010 4:58 PM
    Friday, October 15, 2010 1:06 AM
  • Hi,

    How's everything going? I want to check if the information is helpful or if you need any further assistance. If there is anything unclear, please do not hesitate to respond back.

    Thanks.


    This posting is provided "AS IS" with no warranties, and confers no rights. Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.
    Monday, October 18, 2010 2:59 AM
    Moderator
  • Hi,

    i had problem with understanding sitelink 'relicate every' and schedule of connection between sites. i think that i  know what is going :).

    i will mark answered posts!

    thx you all for clearification.


    Voytas
    Monday, October 18, 2010 4:57 PM