Port 5353 MDNS
Port 5353 is the IANA-assigned mdns port for Multicast DNS (TCP / UDP).
What is port 5353 used for?
Port 5353 is assigned to mdns and uses TCP / UDP. The IANA registry describes the service as “Multicast DNS”. It sits in the registered range, the block used by databases, application servers and developer tooling. Port conflicts here are common when several local services start at once.
Ports are the transport-layer address a service listens on. A client that wants to reach mdns connects to port 5353. A TCP connection is refused when nothing is listening, while a UDP request simply goes unanswered. That is why a port conflict appears whenever two processes try to bind the same number.
Use the commands below to confirm whether port 5353 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.
Browse all DNS and naming ports
Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [IESG]. Reference: [RFC 6762].
Check and block port 5353
Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.
Check on Linux
sudo ss -tlpn 'sport = :5353'
sudo ss -ulpn 'sport = :5353'Check on Windows
Get-NetTCPConnection -LocalPort 5353 -State Listen -ErrorAction SilentlyContinue
Get-NetUDPEndpoint -LocalPort 5353 -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 5353/tcp
sudo ufw deny 5353/udpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 5353 -j DROP
sudo iptables -A INPUT -p udp --dport 5353 -j DROPThese commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.
Is port 5353 safe to expose?
This port is not on our curated list of services with a widely exploited profile. Exposure is only safe when the listening service is intended, patched and protected by a firewall. Keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.
Where port 5353 is usually used
Most traffic on port 5353 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Recursive or authoritative resolution for clients on a LAN or in a VPC.
- Forwarders passing queries between internal and public resolvers.
- Debugging name-resolution failures with dig or nslookup.
Query the resolver
Send one query straight to the server so the answer does not depend on the client's configured resolver.
dig @127.0.0.1 -p 5353 example.comCommon problems with port 5353
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 5353. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.
Port already in use
Find the process holding the port with sudo ss -tlpn 'sport = :5353' or sudo lsof -i :5353. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.
Firewall rule did not survive a reboot
UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.
The port is blocked but still reachable
A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.
Port 5353 at a glance
| Port number | 5353 |
|---|---|
| Service name | mdns |
| Transport protocol | TCP / UDP |
| Category | DNS and naming |
| Range | Registered port (1024–10000) |
| Risk level | Standard/Low |
| Registered assignee | [IESG] |
| Reference | [RFC 6762] |
| Registry description | Multicast DNS |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 5353 used for?
Port 5353 (MDNS) uses TCP / UDP. Multicast DNS.
How do I check if port 5353 is open?
On Linux run `sudo ss -tlpn 'sport = :5353'` and `sudo ss -ulpn 'sport = :5353'`. On Windows run `Get-NetTCPConnection -LocalPort 5353 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 5353 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 5353; empty output usually means nothing is bound to it.
How do I block port 5353?
With UFW run `sudo ufw deny 5353/tcp` and `sudo ufw deny 5353/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 5353 -j DROP` and `sudo iptables -A INPUT -p udp --dport 5353 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 5353 safe to expose?
This port is not on our curated list of services with a widely exploited profile. Exposure is only safe when the listening service is intended, patched and protected by a firewall. Nevertheless, keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.
Related ports
- Port 5350 · pcp-multicastPort Control Protocol Multicast
- Port 5354 · mdnsresponderMulticast DNS Responder IPC
- Port 853 · domain-sDNS query-response protocol run over DTLS or QUIC
- Port 558 · sdnskmpSDNSKMP
- Port 8953 · ub-dns-controlunbound dns nameserver control
- Port 196 · dn6-smm-redDNSIX Session Mgt Module Audit Redir
Primary data: IANA Service Name and Transport Protocol Port Number Registry.
Last reviewed 2026-10-30 · Methodology · About · Privacy