Yesterday i have captured some frames using ethereal... I have noticed that my http requests have the port 32778 ... I wan to know why the client does not use the 80 port and use another one...
Thx

Were you looking at the source or destination port? The destination port from a client will normally be port 80, but it doesn't have to be. If you've followed a link it could potentially send you to another port. If you are looking at the source port on your client, this will be a variable high value, normally starting from 1024 and working upwards, its quite possible for it to be using this as a source port.

Pete

I am talking about the source port. I cannot understand why it is not the same as the destination... Some application use the same port for client and the server but some other does not (ex. apache) Why?

One of the functions of the TCP/UDP layer where ports are used, is to multiplex multiple connections from a single host onto the same destination/source ip addresses. Obviously it is possible to open more than one HTTP session from your PC to a web host. So for each session you have the same source/destination IP pair. So how does the IP stack know which packets go with which session? It does this by using different port numbers.

Now obviously you can't easily go changing the destination port as this identifies to the server which service you want. Hence the term "well known ports" - 23 = telnet, 80 = HTTP, 69 = tftp etc. So to make each session unique the client creates a source port unique to the session so that the source IP and port number taken together, collectively known as a 'socket', uniquely identifies the session.

Where you have a function that does not have multiple potential sessions to the same end-point you tend to have the source and destination ports the same. So for instance RIP uses a source and destination port of 520, because what it sends is an IP and MAC layer broadcast and the information will only ever be sent once from each host so why bother allowing for multiple sessions when there won't ever be multiple sessions?

Its really just a case of each protocol following different design principles to best perform their function without over complicating things.

If you want more in depth info on this, google for 'user datagram protocol rfc', you'll get more info on this than you could ever want!