TCP Port Numbers
Robert Goellner
the things my webbrowser is doing while communicating with a webserver. I
realized, that it increments the portnumber on every http-GET-request ! Does
anybody know, why it is so ?
Thanks a lot !
Robert
Eric A. Hall
When a client opens multiple simultaneous connections to the same
destination, it has to use a different port number.
The four-part tuple which uniquely identifies application traffic is:
src-addr:src-port,dst-addr:dst-port
One of those four elements has to be unique in order to keep data flows
from stepping on each other, so the client uses different source ports for
each connection whenever it has to perform multiple transfers
simultaneously.
More specifically, the application is asking the TCP stack to open a
connection on its behalf, and TCP is allocating the next-available port
number for the connection.
--
Eric A. Hall http://www.ehsco.com/
Internet Core Protocols http://www.oreilly.com/catalog/coreprot/
Robert Goellner
different port numbers for sending and receiving TCP-segments, e.g. is it
possible to send and receive a TCP-segment on a unique port ?
"Eric A. Hall" <eh...@ehsco.com> schrieb im Newsbeitrag
news:3A5E155D...@ehsco.com...
Barry Margolin
Robert Goellner <dab...@addcom.de> wrote:
>One additional question: Am I right if I say, that there is no need of
>different port numbers for sending and receiving TCP-segments, e.g. is it
>possible to send and receive a TCP-segment on a unique port ?
TCP connections are bidirectional. Outgoing traffic on a connection will
be from port A to port B, and incoming traffic on that port will be from
port B to port A.
--
Barry Margolin, bar...@genuity.net
Genuity, Burlington, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.
Alun Jones
wrote:
> > Currently, I dumped some network traffic from my companys LAN and
> > watched the things my webbrowser is doing while communicating with a
> > webserver. I realized, that it increments the portnumber on every
> > http-GET-request ! Does anybody know, why it is so ?
> More specifically, the application is asking the TCP stack to open a
> connection on its behalf, and TCP is allocating the next-available port
> number for the connection.
Note that this particular behaviour makes for a possibility of a port
guessing attack in certain instances.
Alun.
~~~~
[Note that answers to questions in newsgroups are not generally
invitations to contact me personally for help in the future.]
--
Texas Imperial Software | Try WFTPD, the Windows FTP Server. Find us at
1602 Harvest Moon Place | http://www.wftpd.com or email al...@texis.com
Cedar Park TX 78613-1419 | VISA/MC accepted. NT-based sites, be sure to
Fax/Voice +1(512)378-3246 | read details of WFTPD Pro for NT.