These are the ports required for BF4: http://help.ea.com/en/article/online-ports-for-battlefield-4/
Is your PS4 fully up to date?
You may need to contact your ISP as it could be network related.
Here is a band Aid fix. But it is NOT your ISP, NOT your console it is a conflict with the saved profile information on your device (PS4, Xbox's, Computers). I wish people would fact check before wasting everyone's time with nonsense blaming irreverent non applicable theories.
On PS4 you can do this and get a temporary bypass.
1. shut down game hit ps4 button and "push option button" then chose "close application" then confirm by Yes... Now go to the PS4 Setting box or suitcase next to the power button. Click X. Then select "Storage" you will see "system storage" then click then "X" button.
Slide down to "Saved Data". Hit the "X" button again. Highlight "Battlefield 4 tm" then click the "X" button yet again. Now here is the meat and potatoes. you will see "backup saved Data" and ""Profile saved Data"" now highlight the ""profile saved Data"". then on the right it gives you the "DELETE" option and chose "DELETE" with your "X" button NOW BE CAREFUL HERE!!.
ONLY Check the ""Profile Saved Data"" and using the left thumb move to the right to highlight "DELETE" and hit the "X" button and hit "OK" with your "X" Button.
It will say Deleting and take you back to the "Saved Data in System Storage" screen now use the "O" button and hit is 4 times to back to the control panel/Home screen. Now pay attention here, sometimes you can start the game and it will work and other times you must restart or best to shut down the console till it is fully off a (Turn off PS4) and wait till you are sure it is off. On my TV it says NO SIGNAL when the ps4 is fully off.
Now restart the console with the PS4 button on the controller... then start the game and get in a sever. Note sometimes and especially after the Christmas Eve 2017 CRASH of all E.A. servers, you must do this every time you want to change to a different game server on BF4. Sometimes you get lucky and the server has no conflict with your saved profile data.
This is not news with Battlefield and back in the early versions which I played from the first incarnation they also had random odd problems similar to this.
About me: I am a retired CCNA, CCNP, CCIE and worked in Networking for 3 decades. I was an old IBM AS 400 guy, Cisco, 3Com you name it. I brought the Internet from the Dept of Defense A.R.P.A.N.E.T. days to the educational systems (Universities colleges) in the 1980's to eventually building Livingston/Lucent technology boxes and installing them for dial up access to recently building DSLAM's and contract building Cable company ISP's for them to operate and sell you the Internet access and Fiber.
So be careful what people tell you it becomes a chance endeavor and frankly you can eat a banana and try several times and get lucky and get on the server. But this works and many people have let me know it works..
I hope this helps..
