Well-known · Windows

137 NetBIOS Name Service

TCP Yes
UDP Yes
SCTP —
DCCP —

What it is

NetBIOS name registration and resolution.

When / why

Legacy Windows networking. Block at the perimeter; LLMNR/NBT-NS spoofing is a common LAN attack.

Protocol status detail

TransportStatusMeaning
TCP Yes Assigned by IANA and standardized, specified, or widely used on this port.
UDP Yes Assigned by IANA and standardized, specified, or widely used on this port.
SCTP — Not applicable for this transport.
DCCP — Not applicable for this transport.
« 135 MS RPC Endpoint Mapper 138 NetBIOS Datagram »

Port range

Well-known (0–1023). System port for a core service. On Unix-like systems, binding it requires superuser privileges.

Browse all ports →

Firewall rules for port 137

Copy-ready inbound rules for the active transports. Replace every <source> placeholder with the specific host, subnet, or CIDR that should reach this port.

ufw

sudo ufw allow proto tcp from <source> to any port 137

Allow TCP 137 (NetBIOS Name Service). Replace <source> with the network/host that should reach it.

sudo ufw allow proto udp from <source> to any port 137

Allow UDP 137 (NetBIOS Name Service). Replace <source> with the network/host that should reach it.

firewalld

sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="<source>" port port="137" protocol="tcp" accept'

Allow TCP 137 (NetBIOS Name Service) from <source>. Run 'firewall-cmd --reload' afterwards.

sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="<source>" port port="137" protocol="udp" accept'

Allow UDP 137 (NetBIOS Name Service) from <source>. Run 'firewall-cmd --reload' afterwards.

nftables

nft add rule inet filter input ip saddr <source> tcp dport 137 accept

Allow TCP 137 (NetBIOS Name Service). Assumes table 'inet filter' with an 'input' chain.

nft add rule inet filter input ip saddr <source> udp dport 137 accept

Allow UDP 137 (NetBIOS Name Service). Assumes table 'inet filter' with an 'input' chain.

iptables

sudo iptables -A INPUT -p tcp -s <source> --dport 137 -j ACCEPT

Allow TCP 137 (NetBIOS Name Service). Persist with iptables-save/netfilter-persistent.

sudo iptables -A INPUT -p udp -s <source> --dport 137 -j ACCEPT

Allow UDP 137 (NetBIOS Name Service). Persist with iptables-save/netfilter-persistent.

Azure NSG

az network nsg rule create -g <resource-group> --nsg-name <nsg> -n Allow-netbiosnameservice-137 --priority 1000 --access Allow --direction Inbound --protocol "*" --source-address-prefixes <source> --destination-port-ranges 137

Inbound rule for 137 (NetBIOS Name Service). Set <source> to a CIDR; lower priority number = higher precedence.

AWS Security Group

aws ec2 authorize-security-group-ingress --group-id <sg-id> --ip-permissions IpProtocol=tcp,FromPort=137,ToPort=137,IpRanges="[{CidrIp=<source-cidr>}]"

Inbound TCP 137 (NetBIOS Name Service). Replace <source-cidr> (e.g. 10.0.0.0/16).

aws ec2 authorize-security-group-ingress --group-id <sg-id> --ip-permissions IpProtocol=udp,FromPort=137,ToPort=137,IpRanges="[{CidrIp=<source-cidr>}]"

Inbound UDP 137 (NetBIOS Name Service). Replace <source-cidr> (e.g. 10.0.0.0/16).

GCP firewall

gcloud compute firewall-rules create allow-netbiosnameservice-137 --direction=INGRESS --action=ALLOW --rules=tcp:137,udp:137 --source-ranges=<source-cidr> --network=<network>

Ingress rule for 137 (NetBIOS Name Service). Scope with --source-ranges and optionally --target-tags.

Windows netsh

netsh advfirewall firewall add rule name="Allow NetBIOS Name Service 137/TCP" dir=in action=allow protocol=TCP localport=137 remoteip=<source>

Inbound TCP 137 (NetBIOS Name Service). Set remoteip to a host/subnet; 'any' is discouraged.

netsh advfirewall firewall add rule name="Allow NetBIOS Name Service 137/UDP" dir=in action=allow protocol=UDP localport=137 remoteip=<source>

Inbound UDP 137 (NetBIOS Name Service). Set remoteip to a host/subnet; 'any' is discouraged.

Windows PowerShell

New-NetFirewallRule -DisplayName "Allow NetBIOS Name Service 137/TCP" -Direction Inbound -Action Allow -Protocol TCP -LocalPort 137 -RemoteAddress <source>

Inbound TCP 137 (NetBIOS Name Service). Replace <source> with a host or subnet.

New-NetFirewallRule -DisplayName "Allow NetBIOS Name Service 137/UDP" -Direction Inbound -Action Allow -Protocol UDP -LocalPort 137 -RemoteAddress <source>

Inbound UDP 137 (NetBIOS Name Service). Replace <source> with a host or subnet.

Rules are generated only for transports marked active for this port. They default to an inbound allow with an explicit source placeholder — never any. Review direction, scope, and rule precedence before applying in production.