Port 528 (custix)

IANA assigns port 528 to custix: Customer IXChange.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference

custix TCP Customer IXChange Ferdi Ladeira -

custix UDP Customer IXChange Ferdi Ladeira -

Registry dates for this port: last modified 2022-01-25.

Linux: is anything listening on TCP 528?

sudo ss -tlnp 'sport = :528'

Linux: UDP 528

sudo ss -ulnp 'sport = :528'

Linux / macOS: which process owns the port

sudo lsof -nP -i :528

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':528 '

Windows (Command Prompt)

netstat -ano | findstr :528

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 528 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 528

From Windows

Test-NetConnection HOST -Port 528

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

nc -vzu -w 5 HOST 528

ufw

sudo ufw deny 528/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 528 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 528 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 528' -Direction Inbound -Protocol TCP -LocalPort 528 -Action Block

ufw

sudo ufw deny 528/udp

iptables

sudo iptables -A INPUT -p udp --dport 528 -j DROP

nftables

sudo nft add rule inet filter input udp dport 528 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 528' -Direction Inbound -Protocol UDP -LocalPort 528 -Action Block

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