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Port 711 (cisco-tdp)

IANA assigns port 711 to cisco-tdp: Cisco TDP.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
cisco-tdp TCP Cisco TDP Bruce Davie -
cisco-tdp UDP Cisco TDP Bruce Davie -

Check what is listening on port 711

Linux: is anything listening on TCP 711?
sudo ss -tlnp 'sport = :711'
Linux: UDP 711
sudo ss -ulnp 'sport = :711'
Linux / macOS: which process owns the port
sudo lsof -nP -i :711
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':711 '
Windows (Command Prompt)
netstat -ano | findstr :711
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 711 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 711
From Windows
Test-NetConnection HOST -Port 711
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 711

Block port 711 in the firewall

ufw
sudo ufw deny 711/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 711 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 711 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 711' -Direction Inbound -Protocol TCP -LocalPort 711 -Action Block
ufw
sudo ufw deny 711/udp
iptables
sudo iptables -A INPUT -p udp --dport 711 -j DROP
nftables
sudo nft add rule inet filter input udp dport 711 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 711' -Direction Inbound -Protocol UDP -LocalPort 711 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.