Port 11211 (TCP/UDP) — Memcached

Anatoly Oshmanovsky

Port 11211: Memcached

By Anatoly Oshmanovsky · Updated May 23, 2026

Key idea:

Port 11211 (TCP/UDP) is the standard for Memcached. Memcached — in-memory key-value store (pre-Redis era). Port 11211 — default for both TCP and UDP. The UDP variant was used for reflection/amplification DDoS attacks (1.7 Tbps G

Below: what uses this port, security considerations, online check, FAQ.

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What runs on this port

Memcached

Memcached — in-memory key-value store (pre-Redis era). Port 11211 — default for both TCP and UDP. The UDP variant was used for reflection/amplification DDoS attacks (1.7 Tbps GitHub attack 2018). Since then many hosters block UDP 11211 from the outside.

Security considerations

Memcached UDP exposed = amplification DDoS reflector (factor 51,000x). Disable UDP, bind to 127.0.0.1 or private network only. Modern Memcached 1.5.6+ disables UDP by default.

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Understanding Memcached and Its Use Cases

Security Considerations for Using Port 11211

Practical Examples of Configuring Memcached on Port 11211

ICMP PingHost availability and latency

Port ScannerOpen TCP port detection

LatencyResponse time in milliseconds

Packet LossPercentage of dropped packets

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How Do Ping and Port Scanning Work?

Ping sends ICMP packets to a host and measures response time. Port scanning checks which TCP ports are open and accepting connections — helping diagnose serviceavailability issues.

Configurable Ping

Choose packet count (3, 4, 6, 10). Stats: min/avg/max latency and packet loss.

Common Port Scanner

Check 14 key ports: HTTP, HTTPS, SSH, FTP, SMTP, MySQL, PostgreSQL, and more.

Cloud-Based Check

Testing from our server — see site availability from outside, not just your local network.

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Who uses this

DevOps

availability diagnosis

Network engineers

TCP port scanning

Developers

connection debugging

SRE

basic health check

Common Mistakes

❌

ICMP blocked = server is downMany servers block ICMP. Ping fails but site works — check ports instead.

❌

High ping = server problemLatency depends on geography. 150ms between continents is normal, not an error.

❌

Closed ports — cause for alarmClosed ports of unused services are good. Unnecessary open ports are a risk.

❌

One check = sufficientNetworks are unstable. A single timeout ≠ a problem. Check multiple times or set up monitoring.

Best Practices

✓

Combine ping and port checksPing shows host availability, ports show specific service availability. Use both.

✓

Check from different locationsThe problem may be local. A cloud test shows the real picture.

✓

Close unused portsEvery open port is a potential attack vector. Keep only necessary ports open.

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Set up monitoringManual checks do not scale. Set up automated monitoring with notifications.

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Ports

Frequently Asked Questions

Is port 11211 open by default?

No, modern cloud providers (AWS, Google Cloud, Yandex) close all incoming ports by default. You must explicitly allow port 11211 in a Security Group or firewall.

How to check if port 11211 is reachable?

Use <a href="/en/ping">Enterno Ping + Port Checker</a>. Or in shell: <code>nc -vz example.com 11211</code>.

Is port 11211 safe to expose?

Depends on the service. Memcached should never be exposed publicly without authentication + TLS. See <a href="/en/s/research-open-ports-exposure-2026">our 2026 exposure research</a>.

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