Citrix states in their article: CTX325277

CTX325277 - PNAgent appears to cache DNS information

This document was published at: http://support.citrix.com/kb/entry.jspa?externalID=CTX325277

Document ID: CTX325277, Created on: Nov 25, 2002, Updated: Jun 25, 2003

Products: Citrix MetaFrame XP 1.0 for Microsoft Windows 2000, ICA Win32 Program Neighborhood Agent

The below paragraph explains this topic.
ISSUE

The PNAgent may appear to locally Cache the IP address of the NFuse server based upon the following test:

1. Have 2 NFuse servers available and configured.

2. Create a single DNS entry for the fist NFuse server associated with 1 IP address.

3. Set the TTL, time to live, of the record to 10 seconds. This will ensure the record does not stay in the client DNS cache for a long time.

4. Connect with the PNAgent and enumerate the applications.

5. Change the IP address of the DNS record for NFuse to point to a different, 2nd, NFuse server.

6. Shutdown the first NFuse server.

7. Attempt to refresh the application list. The PNAgent will initially fail to connect to the NFuse server as it tries to communicate to the first, now powered off, NFuse server.

EXPLANATION

The code for PNAgent does not cache the IP address. Furthermore, Pnagent does not use the proxy layer code to access config.xml. PNAgent uses the MS Wininet http functions: InternetOpen(), InternetConnect(), HttpSendRequest() et al.

RESOLUTION

Set/Add the client's Internet Explorer DNS cache timeout value to 0. This will disable Internet Explorer's DNS cache.

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Citrix cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

HKEY_CURRENT_USER/Software/Microsoft/Windows/CurrentVersion/Internet Settings/

Value:DnsCacheTimeout

Type: REG_DWORD Value: 0

See Q263558for additional information

Additional Information from the client ReadMe

Version 1051

If an ICA Client's DNS server was configured to use round-robin DNS to map to a set of MetaFrame XP servers, the client did not cycle through the list of resolved addresses. The client attempted to connect only to the first IP address returned by DNS. If the server at the first IP address was unavailable, the client did not try the other IP addresses in the set, and failed to connect. The solution ensures that the client connects, if there is at least one MetaFrame server running in the round-robin DNS set.