Port 5001 DSM (TLS) / iperf3 · TCP

What runs on port 5001

The TLS twin of 5000 in several products: Synology DSM over HTTPS, ASP.NET Core Kestrel HTTPS, and iperf3's default server port (plain TCP/UDP). Identify the service before judging it.

Software that uses it: Synology DSM (HTTPS) · ASP.NET Core · iperf3

Should port 5001 be open?

Internet-facing only with authentication and care. It can be exposed when the service behind it is authenticated, rate-limited and kept up to date; most deployments are better off behind a VPN, an allow-list or a reverse proxy.

• iperf3 -s listens on 5001 by default; -p changes it.

Check port 5001

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :5001'
sudo lsof -i :5001

# from another machine: is it reachable?
nc -zv host 5001
nmap -p 5001 host
curl -v telnet://host:5001      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 5001

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 5001 proto tcp
sudo ufw deny 5001/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 5001 accept
nft add rule inet filter input tcp dport 5001 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 5001 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 5001 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=5001 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 5001" with no source is just "open".

Putting it behind nginx

server {
    listen 443 ssl;
    server_name app.example.com;
    location / {
        proxy_pass http://127.0.0.1:5001;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
    }
}

Then make the application listen on 127.0.0.1:5001 only. Test which location block a request hits with the nginx location tester.

Related ports

• 5000 dev servers — Flask, Docker registry, UPnP
• 443 HTTPS — Web over TLS; UDP for HTTP/3 (QUIC)

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions