Why only TCP?

After careful review, shield's up only test TCP. Is there a reason, it does 
not test UDP?

Thanks. 


0
DSLR
3/7/2008 3:55:46 AM
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On Thu, 6 Mar 2008 22:55:46 -0500, "DSLR user 595148" <user@127.0.0.1>
wrote:

>After careful review, shield's up only test TCP. Is there a reason, it does 
>not test UDP?

Steve advocates "stealth". You cannot both be stealth and test for UDP
ports at the same time, since the reaction from an open UDP port would
be the same as for a stealthed one.

Yet another reason why stealth is utter nonsense. And again, ShieldsUp
is good for one thing and one thing only: To quickly test if a packet
filter is in place either on the machine itself or on a device
somewhere upstream - which makes it a promotion tool more than
anything else.
0
Straight
3/7/2008 5:16:20 AM
DSLR user 595148 wrote:

> After careful review, shield's up only test TCP. Is there a reason, it does 
> not test UDP?

A slightly less inflammatory explanation compared to the one from the 
"other person" here...

The UDP protocol does not have an affirmative "yes, we're open" response 
to a port probe like TCP does. UDP typically will only send a "no, we're 
closed" reply if the tested port is closed. You could infer then that if 
you did *not* receive a message telling you the port was closed that the 
port was open. Unfortunately it's not as simple as that.

If you are running some kind of firewall that blocks all UDP replies and 
have thus "stealthed" your UDP ports, the sender has no way of telling 
the difference between an open port (one that is not sending a "closed" 
response) or one that is firewalled off.

Only if you happen to send a UDP port a piece of data that the service 
using that port recognizes and in turn responds with its own piece of 
data can you definitively claim the port to be open. Steve /could/ do 
this for many common UDP ports but chose not to do so, most likely due 
to the fact that there are many common services running on UDP ports 
that simply do not reply at all to any kind of data, and so his claim 
that the port is "stealthed" may be misleading.

-- 
Robin
0
Robin
3/7/2008 6:12:18 AM
Reply:

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