Re: ip address and ports

From: Barry Margolin (barmar@genuity.net)
Date: 11/26/02 

From: Barry Margolin <barmar@genuity.net>
Date: Tue, 26 Nov 2002 20:27:52 GMT

In article <3DE3D240.2AB71359@yahoo.com>, Lik Mai Sak <alt.test> wrote:
>Tracker wrote:
>
>> > >having an open port
>> > Every PC (server, etc...) on the Internet with an IP address will have
>> > at least one port open.
>> Thousands of malicious hackers would love to get into my computer. On a
>> Windows Platform, no port is open, and am not running any SERVERS.
>
>Really? Go have a squizz at info/RFC's regarding ident.

Does Windows run an IDENT server by default? I don't know for sure, but I
suspect not.

>> > Your browser will, for example, open port 80.
>> Bullcrap, how can a browser open port 80? You really am lost dude.
>> I won't respond to your stupidy.
>> Tracker
>
>It opens port 80/8080/8081/3128 etc on the machine it's connecting to. If it
>didn't, web browsing would not work. (tho establishing a connection to an
>already open port would be more accurate)

Connecting to a server does not cause the client machine to have an open
port. There will be an open socket with a local (usually ephemeral) port
number, but it's not really "open" -- it only processes packets that come
back from the server it's connected to. This port can't be used by someone
to get into your system, which is what someone is generally concerned with
when they talk about "open ports". The most someone can do is forge
packets that appear to be part of that connection, but this requires
knowing the ephemeral port number and sequence numbers that are use in the
connection; unless the attacker is able to sniff the traffic on the
connection, this will be difficult. 

-- 
Barry Margolin, barmar@genuity.net
Genuity, Woburn, 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.

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