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Port 3205 (isns)

IANA assigns port 3205 to isns: iSNS Server Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
isns TCP iSNS Server Port - RFC 4171
isns UDP iSNS Server Port - RFC 4171

Check what is listening on port 3205

Linux: is anything listening on TCP 3205?
sudo ss -tlnp 'sport = :3205'
Linux: UDP 3205
sudo ss -ulnp 'sport = :3205'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3205
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3205 '
Windows (Command Prompt)
netstat -ano | findstr :3205
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3205 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3205
From Windows
Test-NetConnection HOST -Port 3205
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3205

Block port 3205 in the firewall

ufw
sudo ufw deny 3205/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3205 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3205 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3205' -Direction Inbound -Protocol TCP -LocalPort 3205 -Action Block
ufw
sudo ufw deny 3205/udp
iptables
sudo iptables -A INPUT -p udp --dport 3205 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3205 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3205' -Direction Inbound -Protocol UDP -LocalPort 3205 -Action Block

Related ports

3203netwatcher-mon3204netwatcher-db3206ironmail3207vx-auth-port

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