.

NACK data packer - Questions from a certification program

<<

morpheus063

User avatar

Sr. Member
Sr. Member

Posts: 393

Joined: Sun Jun 25, 2006 10:08 am

Location: Cochin - India

Post Fri Jul 07, 2006 12:40 pm

NACK data packer - Questions from a certification program

Hi Friends,

I am posting more questions that I have faced during my course. Please discuss the same. The next question is:

  Code:
Assume that system X sends a NACK data packet to system Y. What does the packet mean?
1.   It means that X does not want to establish a connection.
2.   It means that X did not understand what Y is saying.
3.   It means that X wants to end the connection with Y.
4.   It means that Y wants to end a connection with X.
5.   None of the above.


Regards,
Last edited by morpheus063 on Sun Jan 28, 2007 12:28 pm, edited 1 time in total.
Manu Zacharia
MVP (Enterprise Security), ISLA-2010 (ISC)², C|EH, C|HFI, CCNA, MCP,
Certified ISO 27001:2005 Lead Auditor

[b]There are 3 roads to spoil; women, gambling & hacking. The most pleasant with women, the quickest with gambling, but the surest is hacking - c0c0n
<<

Negrita

User avatar

Sr. Member
Sr. Member

Posts: 299

Joined: Sat Sep 10, 2005 5:45 pm

Location: /dev/null

Post Fri Jul 07, 2006 2:50 pm

Re: NACK data packer - Questions from AFCEH

This is a trick question. If you're rushing through your exam, and don't concentrate you may be tempted to answer no. 1.

The correct answer is;
5. None of the above.

In this situation system Y is sending packets to system X using a TCP session. System X is acknowliging the receipt of these packets by replying with ACK's. If system X fails to receive a packet it will send a NACK to system Y to request a resend of the lost packet.
Last edited by Negrita on Fri Jul 07, 2006 2:59 pm, edited 1 time in total.
CEH, CCSA NG/AI, NNCSS, MCP, MCSA 2003

There are 10 kinds of people, those that understand binary, and those that don't.
<<

morpheus063

User avatar

Sr. Member
Sr. Member

Posts: 393

Joined: Sun Jun 25, 2006 10:08 am

Location: Cochin - India

Post Fri Jul 07, 2006 9:26 pm

Re: NACK data packer - Questions

Hi Negrita,

Thanks for the answer, however, the question is not talking about any TCP session. And I recently came across a defenition of NACK :
A NACK or a non-acknowledgment message is meant for ending the connection, resulting in no further communication between the two systems involved.


Is the above definition is true, and if it is true, then why cant we select the option 3 as the answer.

Thanks for the reply.

Regards,

The Morpheus
Last edited by morpheus063 on Sun Jan 28, 2007 12:29 pm, edited 1 time in total.
Manu Zacharia
MVP (Enterprise Security), ISLA-2010 (ISC)², C|EH, C|HFI, CCNA, MCP,
Certified ISO 27001:2005 Lead Auditor

[b]There are 3 roads to spoil; women, gambling & hacking. The most pleasant with women, the quickest with gambling, but the surest is hacking - c0c0n
<<

pcsneaker

Jr. Member
Jr. Member

Posts: 73

Joined: Mon Nov 07, 2005 12:23 pm

Post Sat Jul 08, 2006 5:02 am

Re: NACK data packer - Questions from AFCEH

To answer that question it would be necessary to know what application/protocol is sending that NACK packet.

At least with TCP/IP (TCP and UDP) there is no "NACK data packet", it can be some upper layer protocol/application (some multicasting data streams use NACKs, DHCP has NACK, etc...)
MCSA:Security (W2k, W2k3)
MCSE:Security (W2k, W2k3)
CPTS, Network+
<<

Negrita

User avatar

Sr. Member
Sr. Member

Posts: 299

Joined: Sat Sep 10, 2005 5:45 pm

Location: /dev/null

Post Sat Jul 08, 2006 4:13 pm

Re: NACK data packer - Questions from AFCEH

The Morpheus, a TCP session can be ended using either a RST or a FIN packet, depending on the situation.
Read here for more info.

pcsneaker, a NACK packet is part of an experimental multicast streaming protocol called Negative-acknowledgment (NACK) Oriented Reliable Multicast protocol or NORM. It has been defined in RFC 3940 and in RFC 3941 and does what I said in my previous post. As you say, there are also DHCP NACKs'.
CEH, CCSA NG/AI, NNCSS, MCP, MCSA 2003

There are 10 kinds of people, those that understand binary, and those that don't.

Return to Network Pen Testing

Who is online

Users browsing this forum: No registered users and 0 guests

cron
.
Powered by phpBB® Forum Software © phpBB Group.
Designed by ST Software