Well-known · Linux/Unix

512 rexec / comsat

TCP Yes
UDP Yes
SCTP —
DCCP —

What it is

Remote process execution (TCP); mail notification comsat (UDP).

When / why

Insecure r-command — replace with SSH.

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.
« 510 FirstClass 513 rlogin / who »

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 512

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 512

Allow TCP 512 (rexec / comsat). Replace <source> with the network/host that should reach it.

sudo ufw allow proto udp from <source> to any port 512

Allow UDP 512 (rexec / comsat). 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="512" protocol="tcp" accept'

Allow TCP 512 (rexec / comsat) from <source>. Run 'firewall-cmd --reload' afterwards.

sudo firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="<source>" port port="512" protocol="udp" accept'

Allow UDP 512 (rexec / comsat) from <source>. Run 'firewall-cmd --reload' afterwards.

nftables

nft add rule inet filter input ip saddr <source> tcp dport 512 accept

Allow TCP 512 (rexec / comsat). Assumes table 'inet filter' with an 'input' chain.

nft add rule inet filter input ip saddr <source> udp dport 512 accept

Allow UDP 512 (rexec / comsat). Assumes table 'inet filter' with an 'input' chain.

iptables

sudo iptables -A INPUT -p tcp -s <source> --dport 512 -j ACCEPT

Allow TCP 512 (rexec / comsat). Persist with iptables-save/netfilter-persistent.

sudo iptables -A INPUT -p udp -s <source> --dport 512 -j ACCEPT

Allow UDP 512 (rexec / comsat). Persist with iptables-save/netfilter-persistent.

Azure NSG

az network nsg rule create -g <resource-group> --nsg-name <nsg> -n Allow-rexeccomsat-512 --priority 1000 --access Allow --direction Inbound --protocol "*" --source-address-prefixes <source> --destination-port-ranges 512

Inbound rule for 512 (rexec / comsat). 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=512,ToPort=512,IpRanges="[{CidrIp=<source-cidr>}]"

Inbound TCP 512 (rexec / comsat). 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=512,ToPort=512,IpRanges="[{CidrIp=<source-cidr>}]"

Inbound UDP 512 (rexec / comsat). Replace <source-cidr> (e.g. 10.0.0.0/16).

GCP firewall

gcloud compute firewall-rules create allow-rexeccomsat-512 --direction=INGRESS --action=ALLOW --rules=tcp:512,udp:512 --source-ranges=<source-cidr> --network=<network>

Ingress rule for 512 (rexec / comsat). Scope with --source-ranges and optionally --target-tags.

Windows netsh

netsh advfirewall firewall add rule name="Allow rexec / comsat 512/TCP" dir=in action=allow protocol=TCP localport=512 remoteip=<source>

Inbound TCP 512 (rexec / comsat). Set remoteip to a host/subnet; 'any' is discouraged.

netsh advfirewall firewall add rule name="Allow rexec / comsat 512/UDP" dir=in action=allow protocol=UDP localport=512 remoteip=<source>

Inbound UDP 512 (rexec / comsat). Set remoteip to a host/subnet; 'any' is discouraged.

Windows PowerShell

New-NetFirewallRule -DisplayName "Allow rexec / comsat 512/TCP" -Direction Inbound -Action Allow -Protocol TCP -LocalPort 512 -RemoteAddress <source>

Inbound TCP 512 (rexec / comsat). Replace <source> with a host or subnet.

New-NetFirewallRule -DisplayName "Allow rexec / comsat 512/UDP" -Direction Inbound -Action Allow -Protocol UDP -LocalPort 512 -RemoteAddress <source>

Inbound UDP 512 (rexec / comsat). 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.