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Port 201 (at-rtmp)

IANA assigns port 201 to at-rtmp: AppleTalk Routing Maintenance.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
at-rtmp TCP AppleTalk Routing Maintenance - -
at-rtmp UDP AppleTalk Routing Maintenance - -

Check what is listening on port 201

Linux: is anything listening on TCP 201?
sudo ss -tlnp 'sport = :201'
Linux: UDP 201
sudo ss -ulnp 'sport = :201'
Linux / macOS: which process owns the port
sudo lsof -nP -i :201
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':201 '
Windows (Command Prompt)
netstat -ano | findstr :201
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 201 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 201
From Windows
Test-NetConnection HOST -Port 201
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 201

Block port 201 in the firewall

ufw
sudo ufw deny 201/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 201 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 201 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 201' -Direction Inbound -Protocol TCP -LocalPort 201 -Action Block
ufw
sudo ufw deny 201/udp
iptables
sudo iptables -A INPUT -p udp --dport 201 -j DROP
nftables
sudo nft add rule inet filter input udp dport 201 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 201' -Direction Inbound -Protocol UDP -LocalPort 201 -Action Block

Related ports

199smux200src202at-nbp203at-3

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