Memcached
What is Port 11211?
Port 11211 is the default port for Memcached, a high-performance, distributed memory caching system. Developed by Brad Fitzpatrick for LiveJournal in 2003, Memcached is used to speed up dynamic web applications by caching data and objects in RAM to reduce database load. Memcached stores key-value pairs and supports operations like get, set, delete, and increment/decrement. It's used by some of the largest websites in the world — Facebook famously ran the world's largest Memcached deployment. While Redis has become a popular alternative with richer data structures, Memcached remains preferred for simple caching scenarios due to its simplicity, multi-threaded architecture, and lower memory overhead per key.
Common Uses
- Database query result caching
- Session storage for web applications
- Page fragment caching
- API response caching
Technical Details
Copy-paste commands to check port 11211 (Memcached) from your terminal
Test connectivity
nc -zv example.com 11211
curl -v --max-time 5 http://example.com:11211/
telnet example.com 11211
nmap -p 11211 -sU -sV example.com
(echo > /dev/tcp/example.com/11211) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 11211/tcp
sudo iptables -A INPUT -p tcp --dport 11211 -j ACCEPT
sudo firewall-cmd --permanent --add-port=11211/tcp && sudo firewall-cmd --reload
Security Considerations
Memcached has no built-in authentication. Thousands of internet-exposed Memcached instances have been exploited for massive DDoS amplification attacks (Memcrashed) — the largest reaching 1.7 Tbps. NEVER expose Memcached to the internet. Bind to localhost or use UNIX sockets. Use firewall rules to restrict access. Disable UDP if not needed (it was the amplification attack vector). Consider SASL authentication if available.
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