socat: The Swiss Army Knife of Networking

I Wanted to Talk About Cool Stuff… But First, socat

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Today I really wanted to jump into more advanced topics, but I realised I first need to address something fundamental.

TCP connections are actually very simple.

Think of them like a phone call:

• You dial → connect
• You talk and listen
• You hang up

Applications basically do the same thing: they open a socket and just read/write data. Everything else (handshakes, retransmissions, congestion control) is handled by the kernel.

But what if we could treat a network connection exactly like a Unix pipe?

That’s where socat comes in.

socat = cat Over the Network

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socat (short for SOcket CAT) lets you create bidirectional byte streams between almost anything: TCP, UDP, files, serial ports, etc.

Simple File Copy Over TCP

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On the receiving side (remotehost):

socat TCP-LISTEN:12345,fork,reuseaddr - > file2

On the sending side (localhost):

cat file1 | socat - TCP:remotehost:12345

That’s it. You just copied a file over the network as easily as cat file1 > file2.

More Advanced: UDP → TCP Proxy

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On the receiving side (remotehost) - that’s the same as previous:

socat TCP-LISTEN:12345,fork,reuseaddr - > file2

On the proxy (middleman):

socat -u UDP-LISTEN:54321,fork TCP:remotehost:12345

And finally on the sending side (localhost):

cat file1 | socat -u - UDP:proxy:54321

That’s it - we just sent the file over UDP and TCP glued together by the TCP-to-UDP proxy.

Real-World Example: SSH Over UDP

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# On remotehost (forward UDP 2222 → local SSH)
socat UDP-LISTEN:2222,reuseaddr,fork TCP:localhost:22

# On localhost (forward local TCP 2222 → remote UDP)
socat TCP-LISTEN:2222,reuseaddr,fork UDP:remotehost:2222

and then just:

ssh -p2222 localhost

!SSH OVER UDP! 🎉

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Why This Matters

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socat proves that at the end of the day, most network communication is just streams of bytes. Once you understand that, you can:

• Forward ports creatively
• Build quick proxies and tunnels
• Debug tricky connectivity issues
• Create powerful one-liners

It really is the Swiss Army knife of networking.

Many other official examples: http://www.dest-unreach.org/socat/doc/socat.html#EXAMPLES

I’ll be showing more advanced socat use cases in future posts (port forwarding, TLS tunnels, relay chains, etc.).