Port 2504Windows Network Load Balancing (NLB)

Windows NLB control traffic uses this port to manage load-balancing hosts; it is not the cluster's application traffic.

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 7/10
lookups: 0

also known as wlbs, Windows Load Balancing Service, NLB, Windows Network Load Balancing

Technical Details

what runs on :2504

The IANA assignment is WLBS on TCP and UDP 2504. In Windows NLB deployments, UDP 2504 is the port associated with NLB control and management; it is not a general-purpose application listener, and the cluster's client traffic is handled on the applications' own ports. The TCP registration does not mean ordinary NLB deployments expose a TCP service here. This is a Windows-specific control protocol rather than a broadly standardized service protocol.

Security Information

exposure of :2504

risk score

7/ 10risk

treat as sensitive. widely scanned and regularly exploited when reachable — restrict it to known sources.

network services averages 2.7 across 1,310 ports — this one sits 4.3 above.

in transit

cleartext

credentials and payloads are readable by anyone on path

assignment

official

registered with iana for this service — scanners fingerprint it by number

reachable over

tcp · udp

udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite

security overview

If NLB remote control is enabled, reachable control traffic can affect cluster operation, so do not expose this port to the public internet; restrict it to trusted management networks and disable remote control when it is not needed. Traffic is not encrypted by default. A port scan finding alone does not establish that NLB is enabled or that its remote-control feature is active.

Record

iana registry entry

port: :2504
service: Windows Network Load Balancing (NLB)
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 7/10risk
category: Network Services
usage: This port is associated with Microsoft's Windows Load Balancing Service, later called Network Load Balancing (NLB), on configured Windows cluster hosts. NLB control or management traffic may use UDP 2504; applications served by the cluster use their own ports.
lookups: 0rank 993
added: 2026-09-23
updated: 2026-09-23
references: IANA service name registry — port 2504

Something wrong?

This record is maintained by the engineers who use port 2504. Every field on it is editable — change what's wrong, say how you know, and a reviewer publishes it, usually within a minute. Last touched 2026-09-23.

01edit any field on a page of its own
02a model checks it for accuracy and spam
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edit this record →back to the registry

Related Ports

all 1,310 in network services →

the 8 most looked-up other ports in network services — 1,310 ports carry that label.

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:3268	Microsoft Global Catalog (GC)	TCPUDP	Security	caution	54.6k
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:3128	Tatsoft Default HTTP Proxy	TCP	Web Services	caution	46.8k

risk mix of the 8 listed

caution100%

0 of 8 encrypted

Port :2504Windows Network Load Balancing (NLB)

Technical Details

Security Information

Related Ports

Port 2504Windows Network Load Balancing (NLB)