What Port 2408 Is
Port 2408 is a registered port in the IANA registry, assigned via TCP to Cloudflare for the Railgun Web Acceleration Protocol (service name: railgun-webaccl). The registration was filed on 2012-03-09, with John Graham-Cumming listed as the contact.1
It is not unassigned. It is not abandoned in the traditional sense. It belongs to a named company for a named protocol. The protocol just no longer exists.
What Railgun Was
Cloudflare Railgun solved a problem that CDNs couldn't touch with caching: dynamic content.
Static files—images, CSS, JavaScript—are easy to cache at the edge. But dynamically generated pages, personalized content, session-aware responses—those can't be cached. Every request goes all the way back to the origin server. For users far from that origin, latency is baked in.
Railgun's answer: don't cache the page. Cache the difference.
The system ran two components:
- A Railgun Sender inside Cloudflare's edge network
- A Railgun Listener installed as a daemon on the customer's origin server
Between them: a persistent, encrypted TCP connection on port 2408. When a request came in for dynamic content, the sender would ask the listener for the page. The listener would compare the current response to the last version it had sent, compress just the delta, and transmit only the changed bytes. If a news site's homepage changed a headline and a timestamp, only those bytes crossed the wire—not the full HTML.
In high-latency situations, this meaningfully reduced transfer size and response time.2
Why It's Dead
Railgun's last significant release was in 2015. For eight years after that, the codebase aged while Cloudflare built newer infrastructure.3
By 2023, Cloudflare had released:
- Cloudflare Tunnel — a more flexible, more secure way to connect origins to the edge
- Argo Smart Routing — intelligent routing that reduces latency without requiring a daemon on your server
- Network Interconnect — direct peering for large customers
Railgun required installing and maintaining a binary on every origin server. The newer products didn't. In June 2023, Cloudflare announced deprecation. On January 31, 2024, Railgun connections stopped functioning.3
The Port Today
Port 2408 remains in the IANA registry under Cloudflare's name. Nothing runs on it by default. If you scan it today on most servers, you'll find it closed.
If you do find something listening on port 2408 on a server that hasn't been decommissioned, it's either:
- A legacy Railgun listener that was never cleaned up
- Something unrelated that chose this port because it appeared unused
How to Check What's Using Port 2408
On Linux/macOS:
On Windows:
From outside the machine:
What the Registered Port Range Means
Port 2408 sits in the registered port range (1024–49151). These ports are tracked by IANA but don't require root/administrator privileges to bind. Applications can claim them by filing with IANA, which Cloudflare did in 2012.
Unlike the well-known ports (0–1023), registered ports are not locked down by the operating system. Any process can open a connection to or listen on port 2408 without special privileges. The IANA registration is a courtesy—a way to say "we're using this, don't collide"—not a technical enforcement.4
Frequently Asked Questions
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