Port 202 is assigned to at-nbp (AppleTalk Name Binding), a service discovery protocol that has been functionally extinct since 2009 when Apple removed AppleTalk support from Mac OS X. This port sits in the well-known range (0-1023), a permanent marker of a protocol that solved zero-configuration networking decades before we pretended to invent it.
What AppleTalk Name Binding Did
The Name Binding Protocol (NBP) was the mechanism that made AppleTalk networks feel like magic. When you opened the Chooser on a Mac in 1990, you saw a list of printers and file servers by name. Not IP addresses. Not manual configuration. Just names. NBP made that happen.1
How it worked:
- Services registered human-readable names when they started ("LaserWriter in Building 3")
- NBP checked that no other machine had claimed that name
- Clients queried the network to find services by name
- Names mapped directly to addresses, completely separate from machine hostnames
The name structure followed the pattern Entity:Type@Zone. A typical query might look for "LaserWriter:Printer@Engineering". NBP would broadcast the query, get responses, and return the address.2
The Assignment History
In April 1988, the Network Information Center (NIC) assigned a range of UDP ports for AppleTalk protocols starting at port 200. Port 202 became the home of at-nbp, documented in RFC 1700 in 1994 and still listed in IANA's registry today.3
The protocol operated on both TCP and UDP at port 202, though UDP was more common for its broadcast-based discovery mechanism.
Why This Mattered (And Still Does)
AppleTalk NBP offered zero-configuration service discovery in 1985. No DHCP server required. No DNS. No manual IP address entry. Two Macs on a network could find each other automatically using multicast.4
This wasn't a prototype or a research project. This was production networking at scale—millions of Macs, printers, and servers used this protocol daily through the 1980s and 1990s. It just worked.
Then we killed it and spent the next decade reinventing it as Multicast DNS (mDNS) and DNS-SD, which Apple released as Bonjour in 2002. The stated goal of mDNS was explicitly "to retire AppleTalk and the AppleTalk Name Binding Protocol and replace them with an IP-based solution."5
The Death of AppleTalk
AppleTalk became unsupported with Mac OS X 10.6 (Snow Leopard) in 2009. Apple removed all legacy AppleTalk support completely with macOS 11 Big Sur in 2020.6
The protocol died because IP networking won. Ethernet became ubiquitous. The Internet happened. AppleTalk's proprietary stack couldn't compete with TCP/IP's universality, even though AppleTalk had better ideas about service discovery and auto-configuration.
What Lives on Port 202 Now
Nothing legitimate, mostly. The protocol assignment remains in IANA's registry as a historical marker, but modern operating systems don't implement AppleTalk. If you see traffic on port 202 today, it's worth investigating—some malware has historically used abandoned well-known ports because they're less likely to raise suspicion.7
Checking Port 202
To see if anything is listening on port 202:
On Linux/Mac:
On Windows:
You shouldn't see anything on modern systems unless you're running very old Apple networking software or something is actively wrong.
Why Unassigned-But-Assigned Ports Matter
Port 202 represents an entire category of ports: officially assigned to protocols that no longer exist in practice. The assignment remains because IANA maintains historical continuity, but the actual service is extinct.
These fossil ports matter because they show us what networking used to be. Port 202 is a reminder that zero-configuration networking worked in 1985, that service discovery doesn't require centralized servers, and that sometimes we solve problems, forget we solved them, and solve them again.
The Name Binding Protocol is dead. Long live mDNS.
Related Ports
- Port 201 - AppleTalk Routing Maintenance (at-rtmp)
- Port 204 - AppleTalk Echo Protocol (at-echo)
- Port 206 - AppleTalk Zone Information (at-zis)
- Port 548 - Apple Filing Protocol (AFP), the file sharing protocol that outlived AppleTalk
Frequently Asked Questions
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