Port 1523 (cichild-lm)

IANA assigns port 1523 to cichild-lm: cichild.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

cichild-lm TCP cichild Andy Burgess -

cichild-lm UDP cichild Andy Burgess -

Linux: is anything listening on TCP 1523?

sudo ss -tlnp 'sport = :1523'

Linux: UDP 1523

sudo ss -ulnp 'sport = :1523'

Linux / macOS: which process owns the port

sudo lsof -nP -i :1523

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':1523 '

Windows (Command Prompt)

netstat -ano | findstr :1523

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1523 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 1523

From Windows

Test-NetConnection HOST -Port 1523

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 1523

ufw

sudo ufw deny 1523/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 1523 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 1523 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 1523' -Direction Inbound -Protocol TCP -LocalPort 1523 -Action Block

ufw

sudo ufw deny 1523/udp

iptables

sudo iptables -A INPUT -p udp --dport 1523 -j DROP

nftables

sudo nft add rule inet filter input udp dport 1523 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 1523' -Direction Inbound -Protocol UDP -LocalPort 1523 -Action Block

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