Port 428 (ocs-cmu, ocs_cmu)

IANA assigns port 428 to ocs-cmu, ocs_cmu: OCS_CMU IANA assigned this well-formed service name as a replacement for "ocs_cmu"..

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

IANA assignment

Service nameProtoDescriptionAssigneeReference

ocs-cmu TCP OCS_CMU IANA assigned this well-formed service name as a replacement for "ocs_cmu". - -

ocs_cmu TCP OCS_CMU
This entry is an alias to "ocs-cmu". This entry is now historic, not usable for use with many common service discovery mechanisms. - -

ocs-cmu UDP OCS_CMU IANA assigned this well-formed service name as a replacement for "ocs_cmu". - -

ocs_cmu UDP OCS_CMU
This entry is an alias to "ocs-cmu". This entry is now historic, not usable for use with many common service discovery mechanisms. - -

Check what is listening on port 428

Linux: is anything listening on TCP 428?

sudo ss -tlnp 'sport = :428'

Linux: UDP 428

sudo ss -ulnp 'sport = :428'

Linux / macOS: which process owns the port

sudo lsof -nP -i :428

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':428 '

Windows (Command Prompt)

netstat -ano | findstr :428

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 428 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 428

From Windows

Test-NetConnection HOST -Port 428

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

nc -vzu -w 5 HOST 428

Block port 428 in the firewall

ufw

sudo ufw deny 428/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 428 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 428 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 428' -Direction Inbound -Protocol TCP -LocalPort 428 -Action Block

ufw

sudo ufw deny 428/udp