## New-Bie doubt in TCP-IP 3 way hand shake

New-Bie doubt in TCP-IP 3 way hand shake
# 1
12-02-2013
New-Bie doubt in TCP-IP 3 way hand shake

from my understanding

step 1:

From device A to device B , sending SYN.
SYN=1
ACK=0
Ackno=0
Sequence number=2000 [for example]

step 2:

from device B to A , sending SYN-ACK
SYN=1
ACK=1
ACKno=2001 [seq no +1]
Sequence number= 5000 [for example]

Step :3

From device A to B , sending ACK

SYN=0
ACK=1
ACKno=5001.
here is my doubt , as i saw in many examples why Sequence number will be 2001 ....?

hope you guys understood my question...
 baker View Public Profile for baker Find all posts by baker
# 2
12-02-2013
It means device B is expecting to hear sequence 2001 (ACK=2001). So in step 3, when ACK is send the SEQ will be 2001.

Refer: RFC 793 (Section 3.4)
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 Yoda View Public Profile for Yoda Visit Yoda's homepage! Find all posts by Yoda
# 3
12-02-2013
I think you are mixing up the sequence numbers and the acknowledgements numbers. They are not related.
 fpmurphy View Public Profile for fpmurphy Find all posts by fpmurphy
# 4
12-02-2013
Quote:
Originally Posted by Yoda
It means device B is expecting to hear sequence 2001 (ACK=2001). So in step 3, when ACK is send the SEQ will be 2001.
thanks , i will be reading the RFC.

but why in step2 , sequence number was having no relation with acknowledge number , but in step3 why sequence number has to be the ACQnumber..?

is there any particular reason for that design..?
 baker View Public Profile for baker Find all posts by baker
# 5
12-03-2013
As per the design, if the ACK flag is set, then only the value of this field is the next sequence number that the receiver is expecting.
 Yoda View Public Profile for Yoda Visit Yoda's homepage! Find all posts by Yoda

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