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Dear Thierry,
Dear Arturas Zalenekas,
AZ> How does TCP protocol work !? How should it replay, e.g. to a closed
port
AZ> !? With ICMP packet !?
Lots of Packetfilters answer with ICMP Administravtively Prohibited,
sometimes also leaking their internal IP address by the way.. It is a
common way to respond every IP stack I know about will understand that
message.
Of course is that a common way. Everything is a common way :) Microsofts
IP stack was/is also build on a "common way" :) Every application CAN work
on a different way with the IP stack. Look at SAP software :)
Thierry, I've seen so many crappy IP stacks in the wild ... that is
terrable. But on the other hand, it is simple to identify the OS. But if
you will see into the RFC 793 (if its not for TCP please correct me) and
RFC 768 (should be UDP), you will understand, what I mean.
AZ> No, it has to answer with an RST.
Answering with ICMP is fine, possible and in the wild.
Of course is it fine. But if you answer with an ICMP packet for a TCP
packet, you can aprox. imagine, what kind of a device or IP stack it is
:)
Thierry, what I would like to say, a lot of developers don't care about
RFCs and I personally hate that. Why do we have RFCs !? Just for fun !?
But that is not the thema. The thema is "how nmap can know my firewalled
servers ?" and it nice to see people wondering, what nmap can :)
Thanks again to the team of nmap.
I'd like to give a tip ... just try to sniff and look "deeper" into
packets, how nmap works. It was at least a help for me.
- --
Kind regards,
Arturas Zalenekas
Network Security Engineer and Analyst
--
http://secdev.zoller.lu
Thierry Zoller
Fingerprint : 5D84 BFDC CD36 A951 2C45 2E57 28B3 75DD 0AC6 F1C7
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