HTTPfy

Port 8243 (synapse-nhttps)

IANA assigns port 8243 to synapse-nhttps: Synapse Non Blocking HTTPS.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
synapse-nhttps TCP Synapse Non Blocking HTTPS Ruwan Linton -
synapse-nhttps UDP Synapse Non Blocking HTTPS Ruwan Linton -

Registry dates for this port: registered 2008-07-10.

Check what is listening on port 8243

Linux: is anything listening on TCP 8243?
sudo ss -tlnp 'sport = :8243'
Linux: UDP 8243
sudo ss -ulnp 'sport = :8243'
Linux / macOS: which process owns the port
sudo lsof -nP -i :8243
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':8243 '
Windows (Command Prompt)
netstat -ano | findstr :8243
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 8243 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 8243
From Windows
Test-NetConnection HOST -Port 8243
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 8243

Block port 8243 in the firewall

ufw
sudo ufw deny 8243/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 8243 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 8243 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 8243' -Direction Inbound -Protocol TCP -LocalPort 8243 -Action Block
ufw
sudo ufw deny 8243/udp
iptables
sudo iptables -A INPUT -p udp --dport 8243 -j DROP
nftables
sudo nft add rule inet filter input udp dport 8243 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 8243' -Direction Inbound -Protocol UDP -LocalPort 8243 -Action Block

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