Port 11211 MEMCACHE
Port 11211 is the IANA-assigned memcache port for Memory cache service (TCP / UDP).
What is port 11211 used for?
Port 11211 is assigned to memcache and uses TCP / UDP. The IANA registry describes the service as “Memory cache service”. It sits above the registered range, where most numbers are transient client ports. A fixed high port is worth documenting precisely because tooling often assumes the default.
Ports are the transport-layer address a service listens on. A client that wants to reach memcache connects to port 11211. 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 11211 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 Caching and in-memory stores ports
Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [Trond_Norbye].
Check and block port 11211
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 = :11211'
sudo ss -ulpn 'sport = :11211'Check on Windows
Get-NetTCPConnection -LocalPort 11211 -State Listen -ErrorAction SilentlyContinue
Get-NetUDPEndpoint -LocalPort 11211 -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 11211/tcp
sudo ufw deny 11211/udpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 11211 -j DROP
sudo iptables -A INPUT -p udp --dport 11211 -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 11211 safe to expose?
Memcached has no authentication and is widely abused for amplification attacks. Bind it to localhost or a private network only. Treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
Where port 11211 is usually used
Most traffic on port 11211 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Session storage, rate limiting and hot-key caching in front of a slower database.
- Several application instances sharing counters or job state on port 11211.
- Local development stacks that run the cache in a container.
Read Memcached stats
The stats command returns counters and memory information; it should never be exposed publicly.
printf 'stats\r\n' | nc 127.0.0.1 11211 | headCommon problems with port 11211
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 11211. 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 = :11211' or sudo lsof -i :11211. 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 11211 at a glance
| Port number | 11211 |
|---|---|
| Service name | memcache |
| Transport protocol | TCP / UDP |
| Category | Caching and in-memory stores |
| Range | High port (10001–65535) |
| Risk level | High |
| Registered assignee | [Trond_Norbye] |
| Registry description | Memory cache service |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 11211 used for?
Port 11211 (MEMCACHE) uses TCP / UDP. Memory cache service.
How do I check if port 11211 is open?
On Linux run `sudo ss -tlpn 'sport = :11211'` and `sudo ss -ulpn 'sport = :11211'`. On Windows run `Get-NetTCPConnection -LocalPort 11211 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 11211 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 11211; empty output usually means nothing is bound to it.
How do I block port 11211?
With UFW run `sudo ufw deny 11211/tcp` and `sudo ufw deny 11211/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 11211 -j DROP` and `sudo iptables -A INPUT -p udp --dport 11211 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 11211 safe to expose?
Memcached has no authentication and is widely abused for amplification attacks. Bind it to localhost or a private network only. Nevertheless, treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
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Primary data: IANA Service Name and Transport Protocol Port Number Registry.
Last reviewed 2026-10-30 · Methodology · About · Privacy