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Port 639 (msdp)

IANA assigns port 639 to msdp: MSDP.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
msdp TCP MSDP Dino Farinacci -
msdp UDP MSDP Dino Farinacci -

Check what is listening on port 639

Linux: is anything listening on TCP 639?
sudo ss -tlnp 'sport = :639'
Linux: UDP 639
sudo ss -ulnp 'sport = :639'
Linux / macOS: which process owns the port
sudo lsof -nP -i :639
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':639 '
Windows (Command Prompt)
netstat -ano | findstr :639
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 639 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 639
From Windows
Test-NetConnection HOST -Port 639
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 639

Block port 639 in the firewall

ufw
sudo ufw deny 639/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 639 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 639 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 639' -Direction Inbound -Protocol TCP -LocalPort 639 -Action Block
ufw
sudo ufw deny 639/udp
iptables
sudo iptables -A INPUT -p udp --dport 639 -j DROP
nftables
sudo nft add rule inet filter input udp dport 639 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 639' -Direction Inbound -Protocol UDP -LocalPort 639 -Action Block

Related ports

637lanserver638mcns-sec640entrust-sps641repcmd

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.