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Port 13821 (dsmcc-download)

IANA assigns port 13821 to dsmcc-download: DSMCC Download Protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
dsmcc-download TCP DSMCC Download Protocol Tim Addington ISO/IEC 13818-6 MPEG-2 DSM-CC
dsmcc-download UDP DSMCC Download Protocol Tim Addington ISO/IEC 13818-6 MPEG-2 DSM-CC

Check what is listening on port 13821

Linux: is anything listening on TCP 13821?
sudo ss -tlnp 'sport = :13821'
Linux: UDP 13821
sudo ss -ulnp 'sport = :13821'
Linux / macOS: which process owns the port
sudo lsof -nP -i :13821
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':13821 '
Windows (Command Prompt)
netstat -ano | findstr :13821
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 13821 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 13821
From Windows
Test-NetConnection HOST -Port 13821
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 13821

Block port 13821 in the firewall

ufw
sudo ufw deny 13821/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 13821 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 13821 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 13821' -Direction Inbound -Protocol TCP -LocalPort 13821 -Action Block
ufw
sudo ufw deny 13821/udp
iptables
sudo iptables -A INPUT -p udp --dport 13821 -j DROP
nftables
sudo nft add rule inet filter input udp dport 13821 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 13821' -Direction Inbound -Protocol UDP -LocalPort 13821 -Action Block

Related ports

13819dsmcc-session13820dsmcc-passthru13822dsmcc-ccp13823bmdss

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