Suppose you want your firewall to block all incoming Telnet connections but to allow outbound Telnet connections. One approach would be to block all inbound packets to the designated Telnet port (23). (a) We might want to block inbound packets to other ports as well, but what inbound TCP connections must be permitted in order not to interfere with outbound Telnet? (b) Now suppose your firewall is allowed to use the TCP header Flags bits in addition to the port numbers. Explain how you can achieve the desired Telnet effect here while at the same time allowing no inbound TCP connections.

Suppose you want your firewall to block all incoming Telnet connections but to allow outbound Telnet connections. One approach would be to block all inbound packets to the designated Telnet port (23). (a) We might want to block inbound packets to other ports as well, but what inbound TCP connections must be permitted in order not to interfere with outbound Telnet? (b) Now suppose your firewall is allowed to use the TCP header Flags bits in addition to the port numbers. Explain how you can achieve the desired Telnet effect here while at the same time allowing no inbound TCP connections.

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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If host A receives two SYN packets from the same port from remote host B, the second may be either a retransmission of the original or, if B has crashed and rebooted, an entirely new connection request. (a) Describe the difference as seen by host A between these two cases. (b) Give an algorithmic description of what the TCP layer needs to do upon receiving a SYN packet. Consider the duplicate/ new cases above and the possibility that nothing is listening to the destination port.
DO NOT COPY FROM OTHER WEBSITES. THANK YOU! Assume that a TCP process A first measures the actual round trip time to another TCP process to be 20 ms, and A thus sets its estimated round trip time to be 20 ms. The next actual round trip time that A sees is 40 ms. In response A increases its estimated round trip to 60 ms. The next actual round trip time that A sees is 30 ms. What is the next estimated round trip computed by A? Justify your answer
Host A and B are directly connected with a 100 Mbps link. There is one TCP connection between the two hosts, and Host A is sending to Host B an enormous file over this connection. Host A can send its application data into its TCP socket at a rate as high as 120 Mbps but Host B can read out of its TCP receive buffer at a maximum rate of 50 Mbps. Describe the effect of TCP flow control.
Why does the maximum packet lifetime have to be large enough to ensure that not only the packet but also its acknowledgments have disappeared? Give one potential disadvantage when Nagle's algorithm is used on a badly congested network. Give two examples of cases where TCP sends data-less packets on an established connection (which is not being torn down).
In your own words, describe what happens at every step of our network model, when a node on one network establishes a TCP connection with a node on another network. You can assume that the two networks are both connected to the same router. You must include a detailed explanation of the following: Physical layer Data link layer Network layer Transport layer MAC address IP address • TCP port Checksum check Routing table TTL
cwmd 35 30 25 20 15 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Transmission Round Assuming TCP Reno is the protocol experiencing the behavior shown above, answer the following questions. a. Identify the intervals of time when TCP slow start is operating. b. Identify the intervals of time when TCP congestion avoidance is operating. c. During what transmission round is the 120th segment sent? (Provide a short discussion justifying your answer.) Congestion Window Size (in segnments)
Hosts A and B have a TCP connection with neither side having any unacknowledged data. Now, host A sends two TCP segments back to back to host B. Host B sends an acknowledgement (ACK) for each segment. Host A receives the second ACK, but not the first one. How many packets does host A retransmit?
We will examine the effect of NATs on P2P applications in this problem. Suppose a peer with Arnold finds that a peer with Bernard username has a file to download. Suppose also that both Bernard and Arnold are behind a NAT. Try to formulate a technique that will permit Arnold to create a TCP link to Bernard without a special NAT application setup. If you have trouble developing such a strategy, please explain why.qap
Consider transferring an enormous file of L bytes from Host A to Host B. Assume an MSS of 536 bytes. a. What is the maximum value of L such that TCP sequence numbers are not exhausted? Recall that the TCP sequence number field has 4 bytes. b. For the L you obtain in (a), find how long it takes to transmit the file. Assume that a total of 66 bytes of transport, network, and data-link header are added to each segment before the resulting packet is sent out over a 155 Mbps link. Ignore flow control and congestion control so A can pump out the segments back to back and continuously.
Assume now that between A and B there is a switch S that uses store and forward. The distance from A to S is m meters and from S to B 2m meters. The link speed between A and S is R bps and between S and B R/2 bps. A has a supply of 6 packets to send to B using UDP. The switch buffer can accommodate 3 packets including the one being transmitted (until it finishes its transmission). Will there be packet losses at the switch buffer. Which packets (number packets 1, 2, 3, ...). Draw an annotated time-space diagram to illustrate this data transmission. (you should roughly respect the scales in your drawing).
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Consider the following figure. Assuming TCP Tahoe is the protocol experiencing the behavior shown above, answer the following questions. In all cases, you should provide a short discussion justifying your ansv answer. 45 40- 35- 30 25 20 15 10 0 2 4 6 8 10 12 14 16 18 20 22 Transmission round • TCP window size as a function of time a) Identify the intervals of time when TCP congestion avoidance is operating. b) What is the value of ssthresh at the 8th transmission round and 20th transmission round, respectively? c) Suppose TCP Reno is used (instead of TCP Reno), and assume that triple duplicate ACKS are received at the 18th round. What are the ssthresh and the congestion window size at the 19th round? d) If there is a timeout event at 21 round, what will be the value of the congestion window size? Congestion window size (segments) 5- 0