6

I'm going to be honest here - this question has been ripped straight from a exam example, but I'm intrigued to see how such a layout would be configured in the real world (I'm not entirely sure of the rules with regards to such a question?)

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Each office contains an identical number of staff. As per the question there is no defined "Head Office" per say.

The options for the answers are as follows:

1. Three Site and Three Site Links
2. Five sites and one site link
3. Five sites and five site links
4. Five sites and three site links

I can see reasoning for two of the options there:

1). Five Sites and Five site links - i.e. Hub and Spoke to perhaps Atlanta.

2). Five Sites and Thee site links - i.e. one site link for all sites connected via the 5Mbps WAN Link, and individual links for the other sites with slower links.

4

You clearly have 5 sites there, so that eliminates option 1. Sites don't necessarily have to correspond to geography, but in reality it practically always works out that way.

There is no connectivity between several of the sites. I.e., the network is not fully meshed. That means you have to unbridge all site links and create specific site links, so that immediately eliminates option 2.

Just remember that even if you have 20 sites that are all fully-routed/meshed, and you have one satellite site that can only talk to one of the other sites... then you must unbridge all site links on account of that one remote site.

Sites that are connected should have their site links bridged.

So you will have:

1 site link New York <> Atlanta.

1 site link Sydney AUS <> Atlanta.

And since Washington, Boston and Atlanta are all fully meshed with equal bandwidth, you can make 1 site link contain all three of those sites so that replication can occur transitively among those sites.

So the answer is option 4. Five sites and three site links.

Option 3, creating five site links, an extra one for Boston <> Atlanta, Washnigton <> Atlanta, and Washington <> Boston, would work OK, but by doing that, you forfeit the transitivity since all sites contained within the same site can replicate transitively. Plus, why create more site links than you have to? It's difficult to really drive that point home in this scenario, but would become a more important factor if your network ever expanded to have more sites.

To further elaborate, just for the sake of completeness - there is a situation where you might want a more extravagant solution for the Washington-Atlanta-Boston network than just a single site link with all three sites in it. And that is if you were bandwidth-constrained between two of the sites - you might want to make a dedicated site link to represent that connection - but give it a higher replication cost, so that the KCC will prefer to replicate across the higher bandwidth, lower cost link... then use a site link bridge to bridge all of the Washington-Atlanta-Boston site links, so that AD would know that it could replicate transitively across the other link in case one of the links went down, but during times of normal operation it knows to prefer the better link. Remember that when calculating site link costing, both site link costs in the transitive route added together need to beat the site link cost of the single point-to-point link, if you want the longer route to be preferred.

But in the words of Einstein, it's best to make things as simple as possible, but no simpler.

  • Ryan - fantastic explanation, thanks very much for taking the time. I realise the question may be seen as an "exam" question however I do believe the theory behind it explained here will be useful for many. – PnP May 11 '15 at 19:04
1

First, to clarify something in the proposed answer, you DO NOT need to unbridge all site links. Just because there is not a mesh topology between sites, does not mean that you do not have an IP route. The only reason to unbridge site links is when you do not have an IP route.

Second, without the wording that goes with the diagram, it is not possible to know exactly what the test thinks is the correct answer. However, I suspect the wording said something like "You must minimize unnecessary traffic on the WAN links while minimizing administrative effort." That wording would lead to only one answer IMO... FIVE SITES WITH THREE SITE LINKS. Establishing 5 sites ensures minimized WAN traffic while combining the three 5Mbps links into a single site link object serves to minimize administrative effort because you have created one site link to represent the 5Mbps links instead of three separate ones. And combining those three links results in the same replication topology and SRV records, if you have DCs in every site.

  • Yeah, you have a point that BASL could be left enabled if, say, New York can route to Boston through Atlanta. But I got the impression that it couldn't. I guess you're right - we can't really know for sure without more detail. – Ryan Ries May 19 '15 at 12:48

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