Port 2135: GRIS — The Grid's Yellow Pages

Port 2135 carries GRIS: the Grid Resource Information Server. It's an LDAP directory service — not for users or login credentials, but for compute clusters. When a job needs to run somewhere across a grid infrastructure, GRIS is how it finds out who's available, what they're running, and how much capacity they have.

What the Port Does

Port 2135 serves LDAP queries over both TCP and UDP. An OpenLDAP daemon (slapd) listens on this port, answering anonymous queries about a cluster's current state: available CPUs, memory, queue depth, supported software, and more.¹

It's a yellow pages for supercomputers. Instead of looking up a person's phone number, you look up a cluster's capabilities.

The port is IANA-registered under the name gris and appears in standard Linux /etc/services files as the canonical home for Grid Resource Information Server traffic.²

The Story Behind the Port

In the early 2000s, physicists at five Nordic universities faced a problem: they each had significant computing resources, but any one institution's cluster was rarely enough for their largest simulations. The obvious answer was to share — but how do you coordinate jobs across clusters at the Niels Bohr Institute in Copenhagen, Helsinki Institute of Physics, Oslo University, and both Lund and Uppsala Universities in Sweden?

They built NorduGrid, and its middleware — the Advanced Resource Connector (ARC) — became one of the first serious grid computing frameworks. The first ARC deployment happened in summer 2002.³

GRIS was the directory layer: before a job could be submitted to a remote cluster, ARC needed to know what that cluster could actually do. Port 2135 became the standard address for that conversation.

The choice of LDAP was deliberate. LDAP was already a mature, hierarchical directory protocol. Rather than invent something new, the NorduGrid team adapted it to serve structured resource information — repurposing a technology designed for corporate user directories to coordinate distributed scientific computing.

The LDAP Choice

LDAP on port 2135 works in anonymous mode — no authentication required for basic resource queries. A cluster joining the grid announces itself; other nodes query it. The directory tree structure maps naturally to grid topology: sites, clusters, queues, individual computing elements.

This openness was intentional. Grid computing depends on resources being discoverable. If you need credentials just to ask "what's available?", the whole federation breaks down.

Is It Still Relevant?

GRIS and the classic NorduGrid LDAP information system are largely legacy technology now. Modern grid and cloud infrastructures have moved toward REST APIs and more sophisticated service discovery systems. The NorduGrid ARC project has evolved its information system through multiple generations, with later versions moving away from LDAP on 2135.⁴

But the port number persists in IANA's registry and in /etc/services files on Linux systems worldwide — a quiet fossil of the era when physicists were figuring out how to make the Internet's spare computing power act like one very large machine.

How to Check What's Listening on This Port

If you see traffic on port 2135 on a system you manage:

On Linux/macOS:

# See what process is listening
ss -tlnp sport = :2135

# Or with lsof
lsof -i :2135

# Try an LDAP query if you suspect GRIS
ldapsearch -x -h localhost -p 2135 -b "o=Grid" "(objectclass=*)"

On Windows:

netstat -ano | findstr :2135

If you're seeing slapd (OpenLDAP) bound to 2135 on a scientific computing system, it's almost certainly a NorduGrid ARC installation or legacy grid middleware.

Port Range

Port 2135 sits in the registered port range (1024–49151). These ports require IANA registration and are typically used by specific applications rather than core Internet infrastructure. Unlike well-known ports (0–1023), they don't require root privileges to bind on most systems.