Open ports slow down my internet connection. How to close them? What to do?

Question

My MacBook Pro has massive problems with internet connectivity. At times the connection is blazingly fast, at times unbelievably slow.
I've spoken to my internet provider who was able to inform me that my computer opens up 500-700 ports which is probably what's slowing down the network connectivity. When I'm online with the MacBook Pro, the web gets unstable – also for other connected devices like iPad etc.
The web supporter asked me to run an anti-virus scan which I did – with no results. The problem persists. When my MacBook Pro is not online, there are approximately 15 ports open, when I log on the web that number increases to between 500 and 700.
Is this normal?
Can anyone tell me how to solve this issue?
How do I figure out which application opens these ports? (and how to close them?)
I tried logging into another user account on the computer and the problem seemed to disappear, indicating that it is caused by something run only on my user account.
Hope someone can help me..

Answer 1

Open ports don't slow down your computer. The tech support person you spoke to doesn't know what they are talking about.
Basically, when you are using a web browser, opening a page means that the browser needs to open a connection for each element in the page (e.g., it needs to grab each picture, CSS, and JavaScript file that the page requires). This could be a couple of dozen, or it could be hundreds (and there's no telling what Flash content on the page will do). The browser tries to mitigate things a bit using a cache (you might check to make sure the cache is turned on, but this is the default setting). However, this is how all browsers work and how the whole system is designed to operate. You cannot "close" any ports, and they don't linger open, they remain open only as long as data is being transferred. This is expected and appropriate behavior.
The most likely culprit is that you are receiving poor DNS service from your service provider. Every time the computer sees an address like 'http://www.google.com', it needs to send out a request to figure out what numerical address goes with the human-readable name. If the DNS service your system is assigned to use doesn't respond lightning-quick, your experience is going to be very sluggish.
You might want to add an external DNS service to your list of DNS providers. Go to System Preferences > Network, select the network you are using on the left (Ethernet or AirPort), and click the 'Advanced' button. Click on the 'DNS' tab, then press the '+' button under the left panel. I would add the OpenDNS.com DNS servers. Add the following DNS addresses:
{quote}
208.67.222.222
208.67.220.220
{quote}
Click the 'OK' button. And then the 'Apply' button to save the changes.
That will probably fix the problem. If it doesn't the next most likely issue is either network congestion (e.g., your ISP's network is just too busy; a very common thing for small ISPs and cable Internet service), or the remote site that you are trying to contact is simply not performing so well.