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Citrix Application performance can be slow, Citrix on Vlan connecting through flat network

Greetings all,

We have a large broadcast domain with a potential of 4000+ nodes.
Currently we have ~1300 nodes on this level 2 switched network.
We have no IPX, but printers/ dhcp/ Lots of RPC etc.

Currently we get ~40MB to the desktop ( of a 100MB line) so far so good.

We recenty installed a Citrix farm (2 nodes) and we decided to place this farm
on a seperate VLAN because there is a lot of broadcast traffic on the flat segment
( The Vlan is attached off the core switch). We are seing delays when
an application goes out to AD to authenticate. Monitoring the packets we are
seeing multiple re-broadcasts and frequent 2 second return delays from the DC
on the flat network back to the Citrix servers on the VLAN.
My boss tells me that "it's not the network" idiot, Active directory is the
problem (Insert your favorite MS snub here). I know I can add another DC
into this VLAN, create a site link and force everything local for authentication.
But looking at the big picture is this the right thing to do since the rest of the production servers ( ie Exchange etc) are back on the flat network space.

We have done tests and the following are the results using backups:

On the flat network on a 1GB interface we get
440.00 MB/Min = 58.6 mbps
We created a special standalone network using a new network and copying the same data between same machines  we get:
1,209 MB/Min = 169.0 mbps

Another datapoint , Active directory;when DC's were in a VLAN on this network
the majority of clients chose to bind to remote DC's over a WAN ( still in the local site). When we added DC's to the flat network then clients bound to them their last
choice was to bind to the DC's in the VLAN. Any thoughts on this?

Anyone have ideas on how to integrate Citrix into a large flat  heavy broadcast based network? My boss expects applications to pop up within 4 seconds.
We are seeing frequent re-broadcasts from Citrix on the Vlan to the main network
and sometimes the syn/acks are 2 seconds. Sometimes it's very fast and seems to
cooincide with network load.

Any suggestions? Or should we just place the Citrix servers on the large flat network?


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1 Solution
Sounds like a router issue to me. To get from one VLAN to another, the packets have to be routed - ie go via a router. The router is probably what's causing the delay. It may not have enough grunt to handle the load being placed on it.

Ideally you want to hang your VLAN's off a layer 3 switch. Basically that will use the router for the first packet that goes between 2 nodes in a different VLAN's, then sends the rest of the packets direct (bypassing the router), which makes things much faster.

Alternatively you could place your Citrix servers on the large flat network. That'll work fine. Surely the broadcast traffic isn't that significant? If it is, you really need to look at ways to reduce it. eg if it's NetBios broadcasts, implement WINS.
welly192Author Commented:
Thanks for your reply, Your thoughts confirm ours. Now If I could only convince our
networking group of this. We have run etherreal against the network and discovered
significant latency. I was told that Citrix will work with slow connections fine, Our Citrix guy
used to implement Citrix over satellite links. However he say's Citrix expects consistancy with
packet returns. We are seeing significant packet retries. Off promary work hours the Citrix
response is damn near remarkable. Applications open faster via citrix than on the local machine.

I'll keep this open for a while longer for any more suggestions


Try giving your network group some additional info that will help them understand that it's a network problem...

From the Citrix server:
ping -n 10 -l 1500 something_else_on_the_same_VLAN
ping -n 10 -l 1500 the_router
ping -n 10 -l 1500 something_on_the_large_flat_network

From the large flat network:
ping -n 10 -l 1500 something_else_on_the_large_flat_network
ping -n 10 -l 1500 the_router
ping -n 10 -l 1500 the_Citrix_server

I'll bet there's packet loss & delays after the router in each case.
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