Port 113 (Ident)

Identification Protocol, still queried by some IRC servers when you connect.

Well-known (system) port, 0-1023 TCP Network infrastructure Do not expose to the internet

What port 113 is used for

Identification Protocol, still queried by some IRC servers when you connect.

Do not expose to the internet. Rarely needed; it can leak user names. Rejecting (rather than dropping) 113 avoids slow IRC connects.

Service nameProtoDescriptionAssigneeReference

auth TCP Authentication Service Mike St Johns -

auth UDP Authentication Service Mike St Johns -

Linux: is anything listening on TCP 113?

sudo ss -tlnp 'sport = :113'

Linux / macOS: which process owns the port

sudo lsof -nP -i :113

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':113 '

Windows (Command Prompt)

netstat -ano | findstr :113

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 113 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 113

From Windows

Test-NetConnection HOST -Port 113

ufw

sudo ufw deny 113/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 113 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 113 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 113' -Direction Inbound -Protocol TCP -LocalPort 113 -Action Block

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