Port 2777: Unassigned — The Legacy RTCP Port That Never Got Registered

What Range This Port Belongs To

Port 2777 falls in the registered ports range (1024–49151). These ports are administered by IANA, and organizations can apply to have a service officially assigned to one. Port 2777 has never been claimed — it appears as unassigned in the IANA Service Name and Transport Protocol Port Number Registry. ¹

That means no service has formal rights to it, but it also means nothing stops someone from using it.

Known Unofficial Uses

Cisco Expressway / VCS — Legacy Firewall Traversal Media

The most concrete real-world use of port 2777 comes from Cisco's enterprise video conferencing infrastructure. Cisco Expressway (formerly VCS) is the system that lets video calls cross corporate firewalls — a hard problem, because media traffic needs to punch through NAT and firewalls in both directions.

Cisco's solution used a technique called Assent (and later H.460.18/H.460.19), which multiplexes RTP and RTCP media through a dedicated port pair on the Expressway-E (the external-facing server). The legacy default for that pair was 2776 for RTP and 2777 for RTCP. ²

When Cisco introduced a wider default range (36000–59999) in later versions, 2776/2777 became the old default — kept around for installations that were never migrated, and still documented in older deployment guides. If you open your firewall logs and see traffic on 2777 in an enterprise network, there is a reasonable chance an aging Expressway or VCS system is still using it.

Polycom — Mail and Calendar Integration

Some Polycom video conferencing documentation from the same era lists port 2777 (TCP) as used for mail and calendar communication with Outlook and Lotus Notes mail servers. ³ This was likely specific to certain firmware versions and collaboration integrations.

Historical Malicious Use

Security databases note that port 2777 has appeared in older trojan and malware traffic. ⁴ This is worth knowing if you see unexpected connections on this port from a system that shouldn't be running Cisco or Polycom infrastructure.

How to Check What Is Listening on This Port

macOS / Linux:

# Show what process is listening on port 2777
lsof -i :2777

# Or with ss (Linux)
ss -tlnp sport = :2777

Windows:

netstat -ano | findstr :2777

Take the PID from the output and cross-reference it:

# macOS / Linux
ps aux | grep <PID>

# Windows
tasklist | findstr <PID>

If something is listening on 2777 that you don't recognize, and you're not running Cisco Expressway, that's worth investigating.

Why Unassigned Ports Matter

The registered port range has 48,128 slots. IANA has formally assigned only a fraction of them. The rest sit unassigned — not empty, just unclaimed.

Vendors pick ports for their products, sometimes never bothering to register them with IANA. Port 2777 is a small example of how the real port landscape diverges from the official one: a port that carried video call media through thousands of corporate firewalls, for years, without a single line in the official registry.