Site links, Site link bridge and bridgehead server

agustinchernitsky

Hello!

I'm reading Syngress book... I'm getting trouble with the following concepts:

* Site links
* Site link bridge
* bridgehead server

What is the difference between the 3 of them? According to the book, all site links are "transitive site link bridges"... but I don't get it when you have to create bridges and when to use a bridgehead server.

Any help appreciated!!

Thanks!

Danman32

Site links are direct links between sites. Site links aren't considered transitive. In other words, if you have site A, B and C, and you have a link between A-B, and B-C, you don't necessarily have a link between A and B. A site link bridge says that to get from A to C, use the links AB and BC.

agustinchernitsky

Hello Danman!

This what syngress book says:

Often, there is no need to deal with site link bridges separately, as all the links are automatically bridged by a property known as a transitive site link. Sometimes when you need to control through which sites the data can flow, you need to create site link bridges. By default, all the site links created are bridged together.

So, if we have A site, B site and C site (A-B and B-C), To get C from A I should create a site link bridge to A where C is one of the "site links in this bridge", right?

Thanks amigo!

agustinchernitsky

Hello again amigo,

This is a quota from ms:

By default, site links are transitive, or “bridged.” If site A has a common site link with site B, site B also has a common site link with Site C, and the two site links are bridged, domain controllers in site A can replicate directly with domain controllers in site C under certain conditions, even though there is no site link between site A and site C. In other words, the effect of bridged site links is that replication between sites in the bridge is transitive.

The setting that implements automatic site link bridges is Bridge all site links, which is found in Active Directory Sites and Services in the properties of the IP or SMTP intersite transport containers. The default bridging of site links occurs automatically and no directory object represents the default bridge. Therefore, in the common case of a fully routed IP network, you do not need to create any site link bridge objects.

Aparently, by default there is "transitivity".

If you want to check the url: http://technet2.microsoft.com/WindowsServer/en/Library/c238f32b-4400-4a0c-b4fb-7b0febecfc731033.mspx?mfr=true

sprkymrk

So did you answer your own question or do you still need help?

A bridgehead server is a specially designated DC that receives replication traffic from another site and replicates it to local site DC's. So if you have DC1, DC2 and DC3 in a site and DCx, DCy, and DCz at another site, you might designate DC1 and DCx as bridgehead servers. This way you don't replicate every 5 minutes across a WAN link with all the DC's at another site. DCs 1,2 and 3 will replicate AD amongst themselves every 5 minutes by default, as will DC's x,y, and z. However, traffic between sites will replicate only on whatever schedule you set, say every 3 hours, and will only replicate from the bridgehead servers DC1 to DCx, which are then responsible to pass that replication information on to other DC's on their respective site.

Danman32

Sorry guys that I didn't complete my post. Someone asked me a question and I needed to get to other threads on this site, so I was going to complete the post later. Then I forgot all about it.

Anyway, yes site bridges are normally automatically created to provide transitivity. But that doesn't have to be the case. I believe there's a checkbox to disable the automatic site bridges. You still need site bridges, but most of the time they are automatically generated and understood. This is one of those things that can be vauge and misleading on a test question.

Do you need site bridges? Well, yes and no. You probably don't need to create any yourself, but they can be automatically generated and implied.

As for bridgeheads, you can designate one DC in a site to receive all updates from other sites that are linked to this site. The bridgehead will apply to all site links to this site.
I don't particularly care much for this idea, since you can't individualize the bridgehead for each link to the site.

agustinchernitsky

Hello sprkymrk & Danman,

Thanks for clearing this out... I believe my confusion was with the site links and the site link bridges... Since the former ones are also by default bridges. That gave me the headache!!

Now, another question... When would you use site link bridges and disable the default transitivity feature? According to Syngress and MS, that would be when you do not have a routed network... Still, I can't think of a good example. Do you guys can think of one?

I think 294 is killing my brain

Thanks a million amigos.

PS: sprkymrk, the MS link shaded some light, buy your explanations were more "human"... I'll stick with the human explanation! LOL!!!

Danman32

Site links and site bridges are not the same thing. Aite links are actual replication links, and site bridges are a collection of links to allow routing between non-adjacent sites.

You may need to take control of the replication path, in which case you would disable the auto-generation of site link bridges and configure the bridges yourself.

For example, you have sites A, B, C, D and E. You create links between A-B, C-D, and D-E. As it is, without bridges, whether auto or manually created, you have no path from A to C, from A to D, from A to E.
You then create a bridge from A to D using link AB and CD. Another bridge might be AB & DE so A can get to E. The system might have created those very same bridges, but perhaps not.

agustinchernitsky

Hello Danman,

That was cristal clear! Thanks a lot.... you should offer some training, you explain quite well

Gracias amigo.

Danman32

Thank you! Hmm, my parents have been encouraging me to teach some classes in their computer club. I have been thinking about creating a seminar in setting up and troubleshooting internet broadband access.

agustinchernitsky

LOL! I tried to teach to my mom once... it was too much a challenge!

Teaching is something I like... I'm giving a course in two months... that for now!

Saludos amigo.