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Port 3113 (cs-auth-svr)

IANA assigns port 3113 to cs-auth-svr: CS-Authenticate Svr Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
cs-auth-svr TCP CS-Authenticate Svr Port Cliff Diamond, Andy Georgiou -
cs-auth-svr UDP CS-Authenticate Svr Port Cliff Diamond, Andy Georgiou -

Check what is listening on port 3113

Linux: is anything listening on TCP 3113?
sudo ss -tlnp 'sport = :3113'
Linux: UDP 3113
sudo ss -ulnp 'sport = :3113'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3113
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3113 '
Windows (Command Prompt)
netstat -ano | findstr :3113
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3113 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3113
From Windows
Test-NetConnection HOST -Port 3113
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3113

Block port 3113 in the firewall

ufw
sudo ufw deny 3113/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3113 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3113 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3113' -Direction Inbound -Protocol TCP -LocalPort 3113 -Action Block
ufw
sudo ufw deny 3113/udp
iptables
sudo iptables -A INPUT -p udp --dport 3113 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3113 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3113' -Direction Inbound -Protocol UDP -LocalPort 3113 -Action Block

Related ports

3111wsynch3112ksysguard3114ccmad3115mctet-master

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