Port 2598 is unassigned by IANA, but in any enterprise running Citrix Virtual Apps and Desktops, it's one of the most consequential ports on the network. It's the reason a doctor can walk from one hospital wing to another without losing their remote session. It's why a trader's screen doesn't go blank when the building's Wi-Fi hiccups.
What It Does
Citrix's standard ICA (Independent Computing Architecture) protocol runs on port 1494. ICA is what carries the remote desktop — keystrokes, screen updates, clipboard data — between a Citrix server and a user's device.
Port 2598 takes over when Session Reliability is enabled. Instead of sending ICA traffic directly, the Citrix client wraps it in a second protocol called CGP (Common Gateway Protocol) and sends the whole package to port 2598. On the server side, a service called XTE receives the CGP-wrapped traffic, strips the wrapper, and hands the inner ICA stream off to the ICA listener on port 1494.
From the application's perspective, nothing changed. From the network's perspective, everything went through 2598.
Why the Wrapper Exists
A raw ICA connection on port 1494 is stateful and unforgiving. Drop the TCP connection for even a few seconds and the session dies. The user gets disconnected. They have to log back in, reopen their applications, find where they were.
CGP adds a buffer. When the client detects a network interruption, it doesn't immediately give up — it queues outgoing data locally and holds the session open, waiting. If the connection recovers within the Session Reliability timeout (typically two minutes by default), the session resumes exactly where it left off. The server never declared the session dead.
Your keystrokes went nowhere. Then the network came back. Then they arrived. The server experienced a pause, not a disconnection.
The Fallback
If the XTE service on the Citrix server fails or is unavailable, the connection falls back to port 1494. This is why production Citrix environments typically keep both ports open in the firewall — 1494 for direct ICA, 2598 for sessions with reliability enabled.
Registered but Unassigned
Port 2598 sits in the registered port range (1024–49151). IANA has not formally assigned it a service name, but Citrix has used it consistently across MetaFrame, XenApp, XenDesktop, and Citrix Virtual Apps and Desktops for over two decades. In practice, if you see traffic on port 2598 in an enterprise environment, it's Citrix.
How to Check What's Using It
If you see something listening on 2598 and you're not running Citrix, investigate. It's not a commonly exploited port, but unassigned ports with active listeners always warrant a look.
Firewall Considerations
In Citrix deployments, the firewall rule is usually straightforward: open TCP 2598 inbound to your Citrix Delivery Controllers or VDAs, alongside TCP 1494. If you're running Citrix Gateway (formerly NetScaler), SSL-wrapped ICA traffic arrives on 443 and is proxied internally — in that case, 2598 may only need to be open for internal traffic between the Gateway and the VDAs.
Related Ports
- 1494 — Standard Citrix ICA without Session Reliability
- 443 — HTTPS; used by Citrix Gateway to carry ICA over SSL externally
- 80 — Citrix StoreFront web interface
Frequently Asked Questions
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