Checking if You're Being Blocked on Outbound Ports

13 Dec 2013

Earlier this week I spent some time playing with Redis on my local dev box. Set-up was smooth sailing; install virtual box w/Ubuntu, Redis, set up port forwarding from a host port to a guest port, grab ServiceStack.Redis...I was on my way. Things got a bit more interesting after I deployed Redis to Azure. I changed the configuration in my little console test application to point to the Azure instance. It was running on the default Redis port, 6379. Fired up the console application...tried a SET. Timed out. Tried it again - same result.

After verifying that the service was running on the box over SSH, I concluded it had to be some outbound filtering. Sure, I could fire up telnet and go to 6379 on my Redis box, but that assumes that there isn't some Azure configuration blocking that port, IPTables isn't blocking that port, and there isn't some Redis configuration I was missing. Those were all important, but I only wanted to verify I was able to get outbound on 6379. Turns out...there is a tool for that: PortQuiz

It's super simple. Basically, the portQuiz server is listening on all ports. This means you can go ahead and telnet to any port. If it times out, you're being filtered outbound. This way, you can be sure it's actually port filtering and not a missing or bad configuration somewhere else in your stack.

So, check it out next time you want to eliminate this as a possibility,

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