Wednesday, February 15, 2017

SSL Reverse Proxy using Citrix NetScaler VPX Express

Part 6 in a series

In previous posts I covered the configuration of the NetScaler VPX Express for use as an intelligent reverse proxy, allowing the use of a single public IP address with multiple interior hosts.

In recent days, I've been working on adding Horizon View to my home lab; in addition to requisite Connection Servers, I'm using the EUC Access Point virtual appliance as a security gateway instead of Security Servers paired with dedicated Connection Servers.

The procedure I outline for the creation of a content-switching configuration works as you'd expect...to a point.

I found that I kept getting "Tunnel reconnection is not permitted" errors when trying to login using the dedicated Horizon Client; this was extremely frustrating because HTML access (using nothing but an HTML5-compatible browser) was working flawlessly.

Upon reviewing the client logs, I noticed that the response from the tunnel connection (HTTP/1.1 404 Not Found) was from IIS, not a Linux or other non-Windows webserver. In my configuration, my content-switching plan uses a Windows IIS server as the fall-through (default/no-match).

Theory: for whatever reason, while the registration process for the Horizon Client was being properly switched to the Access Point, login via tunnel was not.

By capturing a trace (including SSL decoding) at the NetScaler and reviewing it in Wireshark, I was able to see that the client is using two different host strings, one during the initial login followed by a second one during tunnel creation.

What's the difference? The initial login doesn't include the port number in the host string; the tunnel request includes it...
Login: vdi.corp.com
Tunnel: vdi.corp.com:433
The fix is to add an additional match criteria for your content switching policy:
Before: HTTP.REQ.HOSTNAME.EQ("vdi.corp.com")
After: HTTP.REQ.HOSTNAME.EQ("vdi.corp.com")||HTTP.REQ.HOSTNAME.EQ("vdi.corp.com:443")
You can also create an additional policy with the "fqdn:443" match, but editing the policy was faster to implement.

UPDATE: I've done some more digging, and there are additional arguments/functions that would also work—and would've worked transparently had I used them in the first place—instead of the EQ("") expression:
HTTP.REQ.HOSTNAME.CONTAINS("vdi.corp.com")
HTTP.REQ.HOSTNAME.SERVER=="vdi.corp.com"
HTTP.REQ.HOSTNAME.STARTSWITH("vdi.corp.com")
HTTP.REQ.HOSTNAME.PREFIX('.',0).EQ("vdi")

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