Registered · Cross-platform

1521 Oracle DB listener

TCP Yes
UDP Unofficial
SCTP —
DCCP —

What it is

Oracle Net Services default listener (TNS).

When / why

Oracle client connections. Restrict to application servers.

Protocol status detail

TransportStatusMeaning
TCP Yes Assigned by IANA and standardized, specified, or widely used on this port.
UDP Unofficial Not assigned by IANA, but standardized, specified, or widely used on this port.
SCTP — Not applicable for this transport.
DCCP — Not applicable for this transport.
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Port range

Registered (1024–49151). Assigned by IANA on request; usable without elevated privileges on most systems.

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Firewall rules for port 1521

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 1521

Allow TCP 1521 (Oracle DB listener). Replace <source> with the network/host that should reach it.

sudo ufw allow proto udp from <source> to any port 1521

Allow UDP 1521 (Oracle DB listener). 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="1521" protocol="tcp" accept'

Allow TCP 1521 (Oracle DB listener) from <source>. Run 'firewall-cmd --reload' afterwards.

sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="<source>" port port="1521" protocol="udp" accept'

Allow UDP 1521 (Oracle DB listener) from <source>. Run 'firewall-cmd --reload' afterwards.

nftables

nft add rule inet filter input ip saddr <source> tcp dport 1521 accept

Allow TCP 1521 (Oracle DB listener). Assumes table 'inet filter' with an 'input' chain.

nft add rule inet filter input ip saddr <source> udp dport 1521 accept

Allow UDP 1521 (Oracle DB listener). Assumes table 'inet filter' with an 'input' chain.

iptables

sudo iptables -A INPUT -p tcp -s <source> --dport 1521 -j ACCEPT

Allow TCP 1521 (Oracle DB listener). Persist with iptables-save/netfilter-persistent.

sudo iptables -A INPUT -p udp -s <source> --dport 1521 -j ACCEPT

Allow UDP 1521 (Oracle DB listener). Persist with iptables-save/netfilter-persistent.

Azure NSG

az network nsg rule create -g <resource-group> --nsg-name <nsg> -n Allow-oracledblistener-1521 --priority 1000 --access Allow --direction Inbound --protocol "*" --source-address-prefixes <source> --destination-port-ranges 1521

Inbound rule for 1521 (Oracle DB listener). 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=1521,ToPort=1521,IpRanges="[{CidrIp=<source-cidr>}]"

Inbound TCP 1521 (Oracle DB listener). 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=1521,ToPort=1521,IpRanges="[{CidrIp=<source-cidr>}]"

Inbound UDP 1521 (Oracle DB listener). Replace <source-cidr> (e.g. 10.0.0.0/16).

GCP firewall

gcloud compute firewall-rules create allow-oracledblistener-1521 --direction=INGRESS --action=ALLOW --rules=tcp:1521,udp:1521 --source-ranges=<source-cidr> --network=<network>

Ingress rule for 1521 (Oracle DB listener). Scope with --source-ranges and optionally --target-tags.

Windows netsh

netsh advfirewall firewall add rule name="Allow Oracle DB listener 1521/TCP" dir=in action=allow protocol=TCP localport=1521 remoteip=<source>

Inbound TCP 1521 (Oracle DB listener). Set remoteip to a host/subnet; 'any' is discouraged.

netsh advfirewall firewall add rule name="Allow Oracle DB listener 1521/UDP" dir=in action=allow protocol=UDP localport=1521 remoteip=<source>

Inbound UDP 1521 (Oracle DB listener). Set remoteip to a host/subnet; 'any' is discouraged.

Windows PowerShell

New-NetFirewallRule -DisplayName "Allow Oracle DB listener 1521/TCP" -Direction Inbound -Action Allow -Protocol TCP -LocalPort 1521 -RemoteAddress <source>

Inbound TCP 1521 (Oracle DB listener). Replace <source> with a host or subnet.

New-NetFirewallRule -DisplayName "Allow Oracle DB listener 1521/UDP" -Direction Inbound -Action Allow -Protocol UDP -LocalPort 1521 -RemoteAddress <source>

Inbound UDP 1521 (Oracle DB listener). 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.