assignment4

assignment4 - CSC 825 Assignment 4 Avinash Podisetti 1 P25...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
CSC 825 Assignment 4 Avinash Podisetti 1. P25: Host A and B are communicating over a TCP connection, and Host B has already received from Host A all bytes through byte 126. Suppose Host A then sends two segments to Host B back-to-back. The first and second segments contain 70 and 50 bytes of data, respectively. In the first segment, the sequence number is 127, the source port number is 302, and the destination port number is 80. Host B sends an acknowledgement whenever it receives a segment from Host A. 1. In the second segment from Host A to B, what are the sequence number, source port number, and destination port number? Sequence # = (126+(70+1)) = 197 Source Port # = 302 Destination Port # = 80 2. If the first segment arrives before the second segment, in the acknowledgement of the first arriving segment, what is the acknowledgement number, the source port number, and the destination port number? Acknowledgement # = 197 Source Port # = 80 Destination Port # = 302
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
3. If the second segment arrives before the first segment, in the acknowledgement of the first arriving segment, what is the acknowledgement number, the source port number, and the destination port number? Acknowledgement # = 127 Source Port # = 80 Destination Port # = 302 4. Suppose the two segments sent by A arrive in order at B. The first acknowledgement is lost and the second acknowledgement arrives after the first timeout interval. Draw a timing diagram, showing these segments and all other segments and acknowledgements sent. (Assume there is no additional packet loss.) For each segment in your figure, provide the sequence number and the number of bytes of data; for each acknowledgement that you add, provide the acknowledgement number.
Background image of page 2
2. P27: SYN cookies were described in Section 3.5.6. 1. Why is it necessary for the server to use a special initial sequence number in the SYNACK? When sending the SYNACK segment, use an initial sequence # that is a hash of the IP address, port numbers, and a secret value, forget the request When the ACK segment arrives, check the acknowledgement number by recalculating the hash If it matches, assume we have a valid client and proceed If it does not match, reject the connection 2. Suppose an attacker knows that a target host uses SYN cookies. Can the attacker create half-open or fully open connections by simply sending an ACK packet to the target? Why or why not?
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 8

assignment4 - CSC 825 Assignment 4 Avinash Podisetti 1 P25...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online