Port 4011 PXE proxyDHCP · UDP

What runs on port 4011

PXE boot server (proxyDHCP): lets a PXE server answer boot requests on a network whose DHCP server is not PXE-aware. Clients get the boot file name from 4011 and the address from the normal DHCP server.

Software that uses it: dnsmasq (proxy mode) · Windows Deployment Services · FOG · iPXE setups

Should port 4011 be open?

Private network or VPN only. Nothing good comes from this port being reachable from the internet. Keep it on an internal network, reach it over a VPN or an SSH tunnel, and firewall it from everything that does not need it.

• Only needed when you cannot edit the real DHCP server's options 66/67.

Check port 4011

# on the host: is anything listening, and which process?
ss -lunp 'sport = :4011'
sudo lsof -i :4011

# from another machine: is it reachable?
nc -zuv host 4011
sudo nmap -sU -p 4011 host

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 4011

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 4011 proto udp
sudo ufw deny 4011/udp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 udp dport 4011 accept
nft add rule inet filter input udp dport 4011 drop

# iptables (legacy)
iptables -A INPUT -p udp --dport 4011 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 4011 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=4011 protocol=udp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 4011" with no source is just "open".

Related ports

• 67 DHCP server — Hands out IP addresses
• 69 TFTP — Trivial file transfer (PXE boot, network gear)

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