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Port 525 (timed)

IANA assigns port 525 to timed: timeserver.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
timed TCP timeserver - -
timed UDP timeserver - -

Check what is listening on port 525

Linux: is anything listening on TCP 525?
sudo ss -tlnp 'sport = :525'
Linux: UDP 525
sudo ss -ulnp 'sport = :525'
Linux / macOS: which process owns the port
sudo lsof -nP -i :525
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':525 '
Windows (Command Prompt)
netstat -ano | findstr :525
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 525 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 525
From Windows
Test-NetConnection HOST -Port 525
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 525

Block port 525 in the firewall

ufw
sudo ufw deny 525/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 525 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 525 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 525' -Direction Inbound -Protocol TCP -LocalPort 525 -Action Block
ufw
sudo ufw deny 525/udp
iptables
sudo iptables -A INPUT -p udp --dport 525 -j DROP
nftables
sudo nft add rule inet filter input udp dport 525 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 525' -Direction Inbound -Protocol UDP -LocalPort 525 -Action Block

Related ports

523ibm-db2524ncp526tempo527stx

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