Sites, site links, and site link bridges

[Chris Hall]

What is the difference between site links and site link bridges? When would
you use a bridge? Can you add many sites to a site link or should you create
a new site link for each site-to-site connection?

 

[Matjaz Ladava [MVP]]

Site links connect different sites, site link bridges connect different site
links. You would use site link bridges in a network that is not fully
routable as AD by default bridges all site links and in this way connects
every site in ad with every site. You can control this using site link
bridges.

--

Regards

Matjaz Ladava, MCSA, MCSE, MCT, MVP
Microsoft MVP Windows Server - Active Directory
(e-mail address removed), (e-mail address removed)

 

[Chris Hall]

Matjaz,

I guess when you say a 'fully routable' network, that would mean a
persistent connection across WAN links?

Thanks for your response. In the site link properties, there is a parameter:
cost. I'm getting conflicting information on that. One source says that cost
determines the frequency of replication ("Step -by-step Guide to Active
Directory Sites and Services", page 12) and another ("MCSE Guide to
Microsoft Windows 2000 Active Directoy Certification Edition", page 122)
defines cost: "The relative speed of the link in relation to the other links
within the topology...Links with lower costs are faster, whereas links with
higher costs are slower."

Which is correct? What's the 'best' way to configure cost on a network with
few objects and few changes?

 

[Matjaz Ladava [MVP]]

fully routable network is, that there is a WAN path to every site from every
site. There are cases where you can not directly connect from site A to Site
B (because of the firewall), but you can connect trough site C. In this
scenario you would have to configure site link bridges. If there are more
paths to specific site, then the path with the lowest cost would be used.
how often the site is replicating is determined on site link properties when
you set the time when link is available and replication frequency.
AD does not know what is the physical link like (leased, ISDN, DSL, dialup),
so the cost is an imaginary value you can use to tweak replication across
multiple sites.
Both statements are true. If there are multiple paths from one site to
another and each path has different replication settings then cost would
affect replication frequency, as if you change it, then another path could
take precedence with different replication schedule. Other statement, then
links with lower value are faster is also true as the AD replicates trough
the paths with lower value. Again this numbers are used by replication to
chose which path to take when replicating from one site to another.

--

Regards

Matjaz Ladava, MCSA, MCSE, MCT, MVP
Microsoft MVP Windows Server - Active Directory
(e-mail address removed), (e-mail address removed)

 

[Chris Hall]

A lot clearer now! Thanks again!

fully routable network is, that there is a WAN path to every site from every
site. There are cases where you can not directly connect from site A to Site
B (because of the firewall), but you can connect trough site C. In this
scenario you would have to configure site link bridges. If there are more
paths to specific site, then the path with the lowest cost would be used.
how often the site is replicating is determined on site link properties when
you set the time when link is available and replication frequency.
AD does not know what is the physical link like (leased, ISDN, DSL, dialup),
so the cost is an imaginary value you can use to tweak replication across
multiple sites.
Both statements are true. If there are multiple paths from one site to
another and each path has different replication settings then cost would
affect replication frequency, as if you change it, then another path could
take precedence with different replication schedule. Other statement, then
links with lower value are faster is also true as the AD replicates trough
the paths with lower value. Again this numbers are used by replication to
chose which path to take when replicating from one site to another.

--

Regards

Matjaz Ladava, MCSA, MCSE, MCT, MVP
Microsoft MVP Windows Server - Active Directory
(e-mail address removed), (e-mail address removed)