Slingbox and Port Forwarding 21

(Updated 04/03/2012)
Sling Media has made quite a few changes in the last year on how their Sling Player program and SlingBox firmware works in order to eliminate remote viewing problems. The way they have done this is great but at times it can get very confusing.

In order to help you understand what changes they have made and why some people are confused about the port forwarding problems let’s start at the beginning.

Originally in order to connect to your SlingBox remotely you had to have a TCP port forwarded to your SlingBox in your routers configuration setup.  This was the only way you could connect remotely to your SlingBox.

So let’s start with what an open TCP port is and does.

Without going into tons of details of how and what TCP port forwarding does here is a simple explanation.

You have your home network setup with several different things connected to it. Each one of them are given a specific network address.  Not anyone of them can use the same address as the other.  For example the network address of your computer might be and the network address of your Slingbox might be

A TCP port forward is a doorway to your Slingbox. The way it works is that you “open” up this port in your router settings. Then when you are Slinging remotely your SlingPlayer says something like this, in lay man terms, to your router.  “Hey I want to connect to the Slingbox at “” and go through this doorway, a specific port number,  to get there.

Your router then checks to see if that doorway,  port forward, is open to your Slingbox.  If it is then it sends the info to it.  If not open then it says nope can’t go there and stops everything.

So if you don’t have a TCP port forwarded, a doorway,  to your Slingbox then you will be able to reach it.

UDP works completely different.

UDP can tell your router where to send something to. Inside the information packet that it is sending to your home router it also has the place to send the info to in your LAN.

But of course your router needs to know where your Slingbox is.  So your Slingbox sends out to the Sling Media servers where it is at in your LAN and your WAN.

Let’s say your Slingbox is at on your LAN (at home) and on the Internet (WAN).  It tells the Sling Media service this is it’s private home address and here is the public internet address.

Then try to connect to your Slingbox via UDP it sends this info to your router. It tells the router to send this packet of info straight to regardless of what resides at that address. The router doesn’t care it just sends it there without any error checking at all.

That is why you don’t need a port forward setup for the Slingbox and UDP.

How this relates to Slinging

When you setup your SlingBox it tries to setup a TCP port forward for you.  If it or you can’t set one up it will drop back to using UDP to Sling remotely.

The only problem with that your can’t use UDP for everything. It works with the Web SlingPlayer app, both Mac and Windows stand alone programs and I am told also for the iPhone and Blackberry.

I have no way to test the iPhone but have tested UDP usage for the Blackberry and it did not work for me. It also won’t work for the SlingCatcher, Windows Mobile player and Palm Symbian programs.

Ever wonder why someone said “Hey how come my SlingPlayer for Windows works fine remotely but my Catcher doesn’t?” That is because he is using UDP for Windows and there is no proper TCP port forwarded to the SlingBox so the Catcher won’t connect.

This can at times make it very hard to diagnose a remote connection problem. Someone could have a problem using UDP and all he needs to do is open up a TCP port and it goes away. It could also happen in the opposite. Someone having a TCP Slinging issue could try running UDP and see if it helps.

In this case here it resolved his issue completely

That’s the basics of UDP and TCP port forwarding for the Slingbox. If you have any questions regarding this let us know.

In depth resources.

UDP Wikipedia

Understanding UDP

TCP Wikipedia

Introduction to TCP

Leave a comment

21 thoughts on “Slingbox and Port Forwarding

  • Bryanod

    The sling does not stream udp remotely. Your connection will be TCP, Relay or SNATT. It will never show as UDP. The sling stream is tcp always the udp the sling now uses is dependent on upnp enabled routers. The relay and Snatt connections are ways to make remote connections more dependable. TCP is the preferred connection Relay next then snatt.

    Hava users rarely have remote connection configuration issues because it uses the relay of udp ports. Because it never uses TCP its not possible to configure any port. The sling now does the same but its still tcp from the viewing pc and tcp on the sling. UDP is only to get passed the NAT and firewall. So your router is doing more work than a tcp portforward. I think thats why sling support blames routers 90% of the time.

    If you preform a netstat on your remote viewing pc you will see 2 tcp connections (different local ports)to the same port on your wan ip. 5001

  • Naita Rajin

    Your guide is absolutely excellent.
    It has saved me hours of time – since I now know what is the problem with my connection.
    My problem is the speed from my Slingbox Pro HD fluctuates between 1700 and 300 – up and down like a yoyo all the time.
    I now know that it only does this when I connect using TCP, and the problem goes away when I connnect using UDP (SNATT).
    Problem is… If I leave the port forwarding to the wrong port I am unable to connect using my SLINGCATCHER (which requires TCP).
    So my problem is – when using TCP the speed fluctuates horrendously (and so does picture quality). Can you suggest something to fix my TCP problem?

  • Andrew

    I’ve found this article very helpful and I think I’ve figured out that my fluctuating speeds (8000 down to 200 and back) is due to TCP so now my question is, how do I chance to UDP? I know it says to change the port forwarding but I’m not exactly sure what I’m supposed to do! I’m on Verizon FIOS with an ActionTech router.

  • karl

    Bruce,i would try a different port,like 443 or 80,there some others too…..i know comcast has used software to throttle upload/download streaming….so i dont know about other isp’s,but sure they will probaly follow suit….i’m getting ready to try this on my pro hd.

  • between

    My daughter is in the Navy and in Japan, using slingcatcher to use our slingbox and directv dedicated dvr and tv for her use only. After the verizon combo router/modem died I bought a Linksys E3200 router and Verizon sent me a Westell combo router/modem that I bridged to modem only. She then had 2-3 minutes of slinging until it would freeze up. It was a very frustrating looking at all the MTU solutions, this and that, but what worked was changing the Slingbox setup port to 443 from the suggested 5001 and the router port to 443.

  • Eternal Idol

    Bryanod: Actually SNATT is indeed UDP, you can check this by using “Process Monitor” by Sys Internals for example.

    Naita Rajin: Most probably I’m too late but you can add a firewall rule (very easy to do in Windows 7 BTW) to disable the outgoing port your Slingbox uses then it will fallback to UDP.

  • belayon

    I have a few questions:
    a) Is “Relay” mode is actually relaying traffic through Slingmedia servers or is the term Relay referring to the NAT?
    b) What conditions must exist from a Slingbox to connect in TCP mode (not Relay)?
    c) Should a NAT be used for UDP mode or some alternative?

    Trying to understand why I’m always in Relay mode and having connection speeds all over the board…

  • SliderFighter

    I have disabled my TCP NAT and this has put my Slingbox PRO-HD into RELAY mode. Any ideas regarding why this is and/or what I can do to force SNATT mode? My router is NOT UPnP-capable.

  • jamie

    hey. i have had a slingbox for 4 years and a catcher for 3.. “they worked” great until i had this brilliant plan of adding another another slingbox. i bought one off ebay, set it up, did the internet viewing thing.. and it never finished.. so i did it manually like i used to. just added port 5002 and ip thought it was working. but when someone where my catcher is said they keep getting a network error when they try to connect… so brilliant me ran the internet viewing set up on my original slingbox.. now neither of them work… i am pulling my hair out.. i don’t know what is wrong.

    i have 1st slingbox set as port 5001 ip and 2nd 5002 ip
    yet when i run the set up internet viewing. it gets to almost complete do you use these mobel items? click next it asks do do the set up router and test. it goes right back to almost done just need to set up moble items..

    any ideas?

  • jamie

    hey i am able to connect remotely with slingplayer program and though… but when i try my slingcatcher now it says network error..

  • GlennDio

    you guys rock! … I had a slingbox HD and bought a WD TV live to watch my directv at my weekend place … I had a 75/35 Fios connection at the slingbox location and a 40mg Brighthouse connection at the WD TV Live place and couldnt hold anything resembling a good session with a relay connection … I tried to set up the port forwarding a few times with no luck until I used the tools you guys led me to. I went from being miserable about it to having a superb HD experience at my weekend house …BTW the remote commands on the WD TV Live are sluggish but I use a tablet or my smartphone to do the tricky things and then just watch in 48″ HD perfection on the WD TV Live box!

  • Billy

    I read a lot of interesting content here. Probably you spend
    a lot of time writing, i know how to save you a lot of work, there
    is an online tool that creates readable, google friendly
    posts in seconds, just search in google – laranitas free content source