Citrix Zone query


I am looking into the build of a new Citrix 4.5 farm.

We have 2 major sites, and several smaller ones. There will be Citrix servers in both sites (London and Manchester).

But we're not sure of whether it would be a good idea to create two seperate zones, or just build one zone?

What exactly does a zone do, and what are the benefits/disadvantages of having multiple zones?
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Carl WebsterCitrix Technology Professional - FellowCommented:
Citrix recommends as few zones as possible.  When you have multiple zones and have those zones configured to share zone info, you create a lot of network/wan traffic.

You would generally create multiple zones:

to do zone transfer and failover for DR
if you have multiple geo zones that are separated by wide distances and slow wan links
bruce_77Author Commented:
Thanks, to be honest, I am still a little bit confused by what a Zone actually does/is.

For web clients, I understand they connect as follows

Citrix Web Client > Web Interface server > XML Broker > ZDC > PS server

(I assume for Prog Neighbourhood clients, it's PN > ZDC > PS server)

So, if you only had one Zone, then we users in both London and Manchester would be contacting a ZDC in London, which would then send clients to an App server that was least busy.

If we had multiple zones, then users in London would be directed to the London ZDC as above, but users in Manchester would be directed to to the Manchester ZDC > Manchester App servers

Am I along the correct lines?

Finally, is it possible to have multiple zones on the same subnet? I assume not?

Any explanation would be much appreciated!
Carl WebsterCitrix Technology Professional - FellowCommented:
Multiple zones on the same subnet - no.
You would normally have your Citrix servers in one physical location.  So it should matter if you users are in London, Manchester, Grimethorpe or wherever your favorite British Brass Band is located (<grin>).  Since the Citrix ICA protocal is very WAN friendly, you normally want all your servers in one location or as few locations as possible.  That way there is little network distance between servers.

A Zone is simple a collection of servers on a subnet.  In XenApp 5, Citrix finally allows diffeent subnets to be in one Zone since they changed the default naming scheme for Zones.  The new name is "Default" instead of "x.x.x.x".
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from the PS 4.0 advanced concepts guide.  please let me know if you have further questions.

Zones in a server farm perform two functions:
" Collecting data from member servers
" Distributing changes to all servers in the farm
All member servers must belong to a zone. By default, the zone name is the subnet
ID on which the member server resides.
The zone data collector maintains all load and session information for every server
in its zone. Each data collector has a connection open to all other data collectors in
the farm. This connection is used to immediately relay any changes reported by
servers that are members of the zone by that zones data collector to the data
collectors of all other zones. The formula for interzone connections is N * (N-1)/2,
where N is the number of zones in the farm.
Important Citrix recommends that you maintain as few zones as possible while
still being able to complete application enumeration requests and resolutions in a
timely manner. Creating too many zones can decrease performance in a farm,
resulting in high network bandwidth consumption and decreased performance of
the zone data collectors.
bruce_77Author Commented:
Thanks guys, just one question, am I correct in my statement below;

"So, if you only had one Zone, then we users in both London and Manchester would be contacting a ZDC in London, which would then send clients to an App server that was least busy.

If we had multiple zones, then users in London would be directed to the London ZDC as above, but users in Manchester would be directed to to the Manchester ZDC > Manchester App servers"
yep..i think you have it.
if you have Presentation servers in geographically distant places i recommend different zones.
bruce_77Author Commented:

So there is no setting where you can state, if user is connecting from X IP subnet, then direct them to Y PS4.5 servers?

The only way to direct local users to local PS servers (if there are PS server in more than one location) is to use Zones?

Is there also a DR advantage to have multiple Zones as opposed to PS servers spread across the two locations? Without zones, I guess you could have a ZDC in London and a Secondary in Manchester?
you got it.
Carl WebsterCitrix Technology Professional - FellowCommented:
If you have one zone, there can only be one ZDC.  You can setup Most Prefered, Prefered and Default but only one will be a ZDC at one time.  If the ZDC goes out/down, then an election will occur and new one will be selected in about the time you blink an eye.  AT that time, all servers in the zone will send their dynamic info to the ZDC.

If you have multiple Zones, then the same thing happens in each zone.  In addition, you also, by default, have the ZDCs talking to each other.  Citrix doesn't recommend having the ZDCs in each zone talking with other, unless you have a good reason for doing so.  The bandwidth required for inter-zone communication can be intense at times, especially if you have a lot of dynamic activity in the zones.

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