Three Way Handshake Question

[mgodinez]

Dear Greater Cisco Intellect,

Using the Cisco Press CCNA (Intro) text, I ran across the following question:

Select the statement that correctly orders the steps to establish a TCP connection.

Answer: syn=1, syn=1 ack=1, syn=0 ack=1

I need some help deciphering the syn/ack fields here.

I guess syn=1 is the sender and receiver requesting synchronization.

I suppose syn=1 ack=1 is the receiver sending the sender an acknowledgment after synchronization.

But what is syn=0 ack=1?

Any insight would be tremendous to my studies. I would imaging a question like this one being on the test, as every text I've gone through touches on this subject.

Much Obliged,

mgodinez
seattle, wa

partly cloudy...

 

[Jsteve]

Think of it like two people in the dark trying to find each other.
_________________________________________________
the first person yells "Jack I'm here, Hello!" (syn=1)

the second person yells "Jill I'm over here" (syn=1) "and I can here you" (ack=1)

the first person yells "I can here you too" (ack=1)
___________________________________________________

hope you get it. here is a good link that will help you a little more

http://www.cs.ucsb.edu/~vigna/courses/CS176B/TCPIP.pdf

 

[Jsteve]

Also think of syn=0 as if it was not there. If you look at the link above you would see that the sequence is really:
syn=1 ack=0, syn=1 ack=1, syn=0 ack=1

could also be refered to as:
syn=1, syn=1 ack=1, ack=1

 

[mgodinez]

Dear Greater Cisco Intellect,

Thank you for your replies. The three way handshake is clear now. The syn=0 ack=1 (third part of the handshake) was throwin' me off. I thought syn=0 meant that the 2 hosts are not longer synch'd.

Thanks again. I'm plannin' on taking the ccna (intro) exam by the end of the month. I've got a lot of reviewin' to do.

Much Obliged,

mgodinez
seattle, wa

rainy

 

[Jsteve]

good luck

 

[Jsteve]

"I thought syn=0 meant that the 2 hosts are not longer synch'd."

that is what the fin bit is used for.