Simple TCP port numbering question 1

[GusBrown]

Hi all,

I've recently been playing with Ethereal to examine web traffic and I've noticed that each request my browser makes (ie for a page, an image etc) uses a different (incrementing) source port number.
My question is this: does Internet Explorer (and other programs) limit itself to a particular range of ports? How quickly might that port number wrap around?
Or...I wondered whether it's the operating system which assigns that number, to avoid multiple applications using the same one at the same time?

Thanks,

Gus

 

[JasonDeckard]

Gus,

An application does not normally designate which source port to use on an outbound connection (though it is possible to do so if you're writing your own program). This leaves it up to the operating system to identify a source port.

As you have discovered, Windows simply increments the source port number each time. According to Mike Gleason (

http://www.ncftpd.com/ncftpd/doc/misc/ephemeral_ports.html),

the ephemeral port range on Microsoft Windows is 1024-4999, but can support an upper limit of 65534 if you edit the registry.

Regards,
Jason Deckard

http://www.closedsocket.com/

 

[GusBrown]

Thanks Jason, that clears it up.

Gus