Port 517 (talk)

IANA assigns port 517 to talk: like tenex link, but across machine - unfortunately, doesn't use link protocol (this is actually just a rendezvous port from which a tcp connection is established).

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

talk TCP like tenex link, but across machine - unfortunately, doesn't use link protocol (this is actually just a rendezvous port from which a tcp connection is established) - -

talk UDP like tenex link, but across machine - unfortunately, doesn't use link protocol (this is actually just a rendezvous port from which a tcp connection is established) - -

Check what is listening on port 517

Linux: is anything listening on TCP 517?

sudo ss -tlnp 'sport = :517'

Linux: UDP 517

sudo ss -ulnp 'sport = :517'

Linux / macOS: which process owns the port

sudo lsof -nP -i :517

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':517 '

Windows (Command Prompt)

netstat -ano | findstr :517

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 517 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 517

From Windows

Test-NetConnection HOST -Port 517

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 517

Block port 517 in the firewall

ufw

sudo ufw deny 517/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 517 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 517 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 517' -Direction Inbound -Protocol TCP -LocalPort 517 -Action Block

ufw

sudo ufw deny 517/udp