计算机网络自顶向下方法第八版答案 14.56MB

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SM8th.zip 大约有13个文件

SM8th/SM - Computer Networking 8e Kurose.pdf 6.44MB
SM8th/Wireshark_802.11_SOLUTION_v8.0.doc 171.5KB
SM8th/Wireshark_DHCP_SOLUTION_v8.0.doc 298.5KB
SM8th/Wireshark_DNS_SOLUTION_V8.0.docx 599.82KB
SM8th/Wireshark_Ethernet_ARP_SOLUTION_v8.0.doc 389.5KB
SM8th/Wireshark_HTTP_SOLUTION_v8.0.doc 4.36MB
SM8th/Wireshark_ICMP_SOLUTION_v8.0.doc 462.5KB
SM8th/Wireshark_Intro_SOLUTION_v8.0.doc 434KB
SM8th/Wireshark_IP_SOLUTION_V8.0.docx 333.71KB
SM8th/Wireshark_NAT_SOLUTION_v8.0.doc 161.5KB
SM8th/Wireshark_SSL_SOLUTION_v8.0.doc 1.52MB
SM8th/Wireshark_TCP_SOLUTION_v8.0.doc 1.43MB
SM8th/Wireshark_UDP_SOLUTION_v8.0.doc 298.5KB

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自顶向下方法第八版答案，包括复习题以及课后习题和实验的内容。

<html xmlns="http://www.w3.org/1999/xhtml"><meta charset="utf-8"><meta name="generator" content="pdf2htmlEX"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><link rel="stylesheet" href="/image.php?url=https://csdnimg.cn/release/download_crawler_static/css/base.min.css"><link rel="stylesheet" href="/image.php?url=https://csdnimg.cn/release/download_crawler_static/css/fancy.min.css"><link rel="stylesheet" href="/image.php?url=https://csdnimg.cn/release/download_crawler_static/87768255/raw.css"><script src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/js/compatibility.min.js"></script><script src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/js/pdf2htmlEX.min.js"></script><script>try{pdf2htmlEX.defaultViewer = new pdf2htmlEX.Viewer({});}catch(e){}</script><div id="sidebar" style="display: none"><div id="outline"></div></div><div id="pf1" class="pf w0 h0" data-page-no="1"><div class="pc pc1 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/87768255/bg1.jpg"><div class="c x1 y1 w2 h2"><div class="t m0 x0 h3 y2 ff1 fs0 fc0 sc0 ls0 ws0"></div></div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div></html><div id="pf2" class="pf w0 h0" data-page-no="2"><div class="pc pc2 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/87768255/bg2.jpg"><div class="c x2 y3 w3 h4"><div class="t m0 x3 h5 y4 ff2 fs1 fc2 sc0 ls1 ws0">Chapter!1!Review!Questions!</div></div><div class="t m0 x4 h6 y5 ff3 fs2 fc0 sc0 ls0 ws0">1. There is no difference. Throughout this text, the words “host” and “end system” are</div><div class="t m0 x5 h6 y6 ff3 fs2 fc0 sc0 ls0 ws0">used interchangeably. End systems include PCs, workstations, Web servers, mail</div><div class="t m0 x5 h6 y7 ff3 fs2 fc0 sc0 ls0 ws0">servers, PDAs, Internet-connected game consoles, etc.</div><div class="t m0 x4 h6 y8 ff3 fs2 fc0 sc0 ls0 ws0">2. From Wikipedia: Diplomatic protocol is commonly described as a set of international</div><div class="t m0 x5 h6 y9 ff3 fs2 fc0 sc0 ls0 ws0">courtesy rules. These well-established and time-honored rules have made it easier for</div><div class="t m0 x5 h6 ya ff3 fs2 fc0 sc0 ls0 ws0">nations and people to live and work together. Part of protocol has always been the</div><div class="t m0 x5 h6 yb ff3 fs2 fc0 sc0 ls0 ws0">acknowledgment of the hierarchical standing of all present. Protocol rules are based on</div><div class="t m0 x5 h6 yc ff3 fs2 fc0 sc0 ls0 ws0">the principles of civility.</div><div class="t m0 x4 h6 yd ff3 fs2 fc0 sc0 ls0 ws0">3. Standards are important for protocols so that people can create networking systems and</div><div class="t m0 x5 h6 ye ff3 fs2 fc0 sc0 ls0 ws0">products that interoperate.</div><div class="t m0 x4 h6 yf ff3 fs2 fc0 sc0 ls0 ws0">4. 1. Dial-up modem over telephone line: home; 2. DSL over telephone line: home or</div><div class="t m0 x5 h6 y10 ff3 fs2 fc0 sc0 ls6 ws0">small office; 3. Cable to HFC: home; 4. 100 Mbps switched Ethernet: enterprise.</div><div class="t m0 x4 h6 y11 ff3 fs2 fc0 sc0 ls0 ws0">5. HFC bandwidth is shared among the users. On the downstream channel, all packets</div><div class="t m0 x5 h6 y12 ff3 fs2 fc0 sc0 ls0 ws0">emanate from a single source, namely, the head end. Thus, there are no collisions in</div><div class="t m0 x5 h6 y13 ff3 fs2 fc0 sc0 ls0 ws0">the downstream channel.</div><div class="t m0 x4 h6 y14 ff3 fs2 fc0 sc0 ls0 ws0">6. In most American cities, the current possibilities include: dial-up; DSL; cable modem;</div><div class="t m0 x5 h6 y15 ff3 fs2 fc0 sc0 ls0 ws0">fiber-to-the-home.</div><div class="t m0 x4 h6 y16 ff3 fs2 fc0 sc0 ls0 ws0">7. Ethernet LANs have transmission rates of 10 Mbps, 100 Mbps, 1 Gbps and 10 Gbps.</div><div class="t m0 x4 h6 y17 ff3 fs2 fc0 sc0 ls0 ws0">8. Today, Ethernet most commonly runs over twisted-pair copper wire. It also can run over</div><div class="t m0 x5 h6 y18 ff3 fs2 fc0 sc0 ls0 ws0">fibers optic links.</div><div class="t m0 x4 h6 y19 ff3 fs2 fc0 sc0 ls0 ws0">9. ADSL: up to 24 Mbps downstream and 2.5 Mbps upstream, bandwidth is dedicated;</div><div class="t m0 x5 h6 y1a ff3 fs2 fc0 sc0 ls0 ws0">HFC, rates up to 42.8 Mbps and upstream rates of up to 30.7 Mbps, bandwidth is</div><div class="t m0 x5 h6 y1b ff3 fs2 fc0 sc0 ls0 ws0">shared. FTTH: 2-10Mbps upload; 10-20 Mbps download; bandwidth is not shared.</div><div class="t m0 x4 h6 y1c ff3 fs2 fc0 sc0 ls0 ws0">10. There are two popular wireless Internet access technologies today:</div><div class="t m0 x6 h6 y1d ff3 fs2 fc0 sc0 ls5 ws0">a. Wifi (802.11) In a wireless LAN, wireless users transmit/receive packets</div><div class="t m0 x7 h6 y1e ff3 fs2 fc0 sc0 ls0 ws0">to/from an base station (i.e., wireless access point) within a radius of few tens</div><div class="t m0 x7 h6 y1f ff3 fs2 fc0 sc0 ls0 ws0">of meters. The base station is typically connected to the wired Internet and thus</div><div class="t m0 x7 h6 y20 ff3 fs2 fc0 sc0 ls0 ws0">serves to connect wireless users to the wired network.</div><div class="t m0 x6 h6 y21 ff3 fs2 fc0 sc0 ls0 ws0">b. 3G and 4G wide-area wireless access networks. In these systems, packets are</div><div class="t m0 x7 h6 y22 ff3 fs2 fc0 sc0 ls0 ws0">transmitted over the same wireless infrastructure used for cellular telephony,</div><div class="t m0 x7 h6 y23 ff3 fs2 fc0 sc0 ls6 ws0">with the base station thus being managed by a telecommunications provider.</div><div class="t m0 x7 h6 y24 ff3 fs2 fc0 sc0 ls0 ws0">This provides wireless access to users within a radius of tens of kilometers of</div><div class="t m0 x7 h6 y25 ff3 fs2 fc0 sc0 ls0 ws0">the base station.</div><div class="t m0 x4 h6 y26 ff3 fs2 fc0 sc0 ls0 ws0">11. At time t</div><div class="t m0 x8 h7 y27 ff3 fs3 fc0 sc0 ls0 ws0">0</div><div class="t m0 x9 h6 y26 ff3 fs2 fc0 sc0 ls0 ws0"> the sending host begins to transmit. At time t</div><div class="t m0 xa h8 y27 ff4 fs3 fc0 sc0 ls0 ws0">1 </div><div class="t m0 xb h9 y26 ff4 fs2 fc0 sc0 ls0 ws0">= L/R</div><div class="t m0 xc h8 y27 ff4 fs3 fc0 sc0 ls0 ws0">1</div><div class="t m0 xd h6 y26 ff3 fs2 fc0 sc0 ls0 ws0">, the sending host</div><div class="t m0 x5 h6 y28 ff3 fs2 fc0 sc0 ls0 ws0">completes transmission and the entire packet is received at the router (no propagation</div><div class="t m0 x5 h6 y29 ff3 fs2 fc0 sc0 ls0 ws0">delay). Because the router has the entire packet at time t</div><div class="t m0 xe h8 y2a ff4 fs3 fc0 sc0 ls0 ws0">1</div><div class="t m0 xf h6 y29 ff3 fs2 fc0 sc0 ls0 ws0">, it can begin to transmit the</div><div class="c x1 y2b w4 ha"><div class="t m0 x0 hb y2c ff5 fs4 fc0 sc0 ls0 ws0">© 2020 Pearson Education, Hoboken, NJ. All rights reserved.</div></div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div><div id="pf3" class="pf w0 h0" data-page-no="3"><div class="pc pc3 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/87768255/bg3.jpg"><div class="c x2 y3 w3 h4"><div class="t m0 x3 hc y2d ff6 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x3 hc y2e ff6 fs2 fc0 sc0 ls0 ws0"> </div></div><div class="t m0 x5 h6 y2f ff3 fs2 fc0 sc0 ls0 ws0">packet to the receiving host at time t</div><div class="t m0 x10 h8 y30 ff4 fs3 fc0 sc0 ls0 ws0">1</div><div class="t m0 x11 h6 y2f ff3 fs2 fc0 sc0 ls0 ws0">. At time t</div><div class="t m0 x12 h8 y30 ff4 fs3 fc0 sc0 ls0 ws0">2</div><div class="t m0 x13 h9 y2f ff4 fs2 fc0 sc0 ls0 ws0"> = t</div><div class="t m0 x14 h8 y30 ff4 fs3 fc0 sc0 ls0 ws0">1</div><div class="t m0 x15 h9 y2f ff4 fs2 fc0 sc0 ls0 ws0"> + L/R</div><div class="t m0 x16 h8 y30 ff4 fs3 fc0 sc0 ls0 ws0">2</div><div class="t m0 x17 h6 y2f ff3 fs2 fc0 sc0 ls0 ws0">, the router completes </div><div class="t m0 x5 h6 y31 ff3 fs2 fc0 sc0 ls0 ws0">transmission and the entire packet is received at the receiving host (again, no </div><div class="t m0 x5 h6 y32 ff3 fs2 fc0 sc0 ls0 ws0">propagation delay). Thus, the end-to-end delay is L/R</div><div class="t m0 x18 h8 y33 ff4 fs3 fc0 sc0 ls0 ws0">1</div><div class="t m0 x19 h9 y32 ff4 fs2 fc0 sc0 ls0 ws0"> + L/R</div><div class="t m0 xb h8 y33 ff4 fs3 fc0 sc0 ls0 ws0">2</div><div class="t m0 x1a h6 y32 ff3 fs2 fc0 sc0 ls0 ws0">. </div><div class="t m0 x4 h6 y34 ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x4 h6 y35 ff3 fs2 fc0 sc0 ls0 ws0">12. A circuit-switched network can guarantee a certain amount of end-to-end bandwidth </div><div class="t m0 x5 h6 y36 ff3 fs2 fc0 sc0 ls0 ws0">for the duration of a call. Most packet-switched networks today (including the Internet) </div><div class="t m0 x5 h6 y37 ff3 fs2 fc0 sc0 ls0 ws0">cannot make any end-to-end guarantees for bandwidth. FDM requires sophisticated </div><div class="t m0 x5 h6 y38 ff3 fs2 fc0 sc0 ls0 ws0">analog hardware to shift signal into appropriate frequency bands. </div><div class="t m0 x4 h6 y39 ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x4 hd y3a ff3 fs2 fc0 sc0 ls0 ws0">13. a) 2 users can be supported because each user requires half of the link bandwidth. </div><div class="t m0 x4 h6 y3b ff3 fs2 fc0 sc0 ls0 ws0"> b) Since each user requires 1Mbps when transmitting, if two or fewer users transmit </div><div class="t m0 x4 h6 y3c ff3 fs2 fc0 sc0 ls0 ws0"> simultaneously, a maximum of 2Mbps will be required. Since the available </div><div class="t m0 x4 h6 y3d ff3 fs2 fc0 sc0 ls0 ws0"> bandwidth of the shared link is 2Mbps, there will be no queuing delay before the </div><div class="t m0 x4 h6 y3e ff3 fs2 fc0 sc0 ls0 ws0"> link. Whereas, if three users transmit simultaneously, the bandwidth required </div><div class="t m0 x4 h6 y3f ff3 fs2 fc0 sc0 ls0 ws0"> will be 3Mbps which is more than the available bandwidth of the shared link. In </div><div class="t m0 x4 hd y40 ff3 fs2 fc0 sc0 ls0 ws0"> this case, there will be queuing delay before the link. </div><div class="t m0 x4 h6 y41 ff3 fs2 fc0 sc0 ls0 ws0"> c) Probability that a given user is transmitting = 0.2 </div><div class="t m0 x4 h6 y42 ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x4 h6 y43 ff3 fs2 fc0 sc0 ls0 ws0"> d) Probability that all three users are transmitting simultaneously = </div><div class="t m0 x4 h6 y44 ff4 fs2 fc0 sc0 ls0 ws0"> = (0.2)</div><div class="t m0 x1b h7 y45 ff3 fs3 fc0 sc0 ls0 ws0">3 </div><div class="t m0 x1c h6 y44 ff3 fs2 fc0 sc0 ls0 ws0">= 0.008. Since the queue grows when all the users are transmitting, the </div><div class="t m0 x4 h6 y46 ff3 fs2 fc0 sc0 ls0 ws0"> fraction of time during which the queue grows (which is equal to the probability </div><div class="t m0 x4 h6 y47 ff3 fs2 fc0 sc0 ls0 ws0">that all three users are transmitting simultaneously) is 0.008. </div><div class="t m0 x4 h6 y48 ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x4 h6 y49 ff3 fs2 fc0 sc0 ls0 ws0">14. If the two ISPs do not peer with each other, then when they send traffic to each other </div><div class="t m0 x5 h6 y4a ff3 fs2 fc0 sc0 ls0 ws0">they have to send the traffic through a provider ISP (intermediary), to which they have </div><div class="t m0 x5 h6 y4b ff3 fs2 fc0 sc0 ls5 ws0">to pay for carrying the traffic. By peering with each other directly, the two ISPs can </div><div class="t m0 x5 h6 y4c ff3 fs2 fc0 sc0 ls0 ws0">reduce their payments to their provider ISPs. An Internet Exchange Points (IXP) </div><div class="t m0 x5 h6 y4d ff3 fs2 fc0 sc0 ls0 ws0">(typically in a standalone building with its own switches) is a meeting point where </div><div class="t m0 x5 h6 y4e ff3 fs2 fc0 sc0 ls5 ws0">multiple ISPs can connect and/or peer together. An ISP earns its money by charging </div><div class="t m0 x5 h6 y4f ff3 fs2 fc0 sc0 ls5 ws0">each of the the ISPs that connect to the IXP a relatively small fee, which may depend </div><div class="t m0 x5 h6 y50 ff3 fs2 fc0 sc0 ls0 ws0">on the amount of traffic sent to or received from the IXP. </div><div class="t m0 x5 h6 y51 ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x4 h6 y52 ff3 fs2 fc0 sc0 ls0 ws0">15. Google's private network connects together all its data centers, big and small. Traffic </div><div class="t m0 x5 h6 y53 ff3 fs2 fc0 sc0 ls0 ws0">between the Google data centers passes over its private network rather than over the </div><div class="t m0 x5 h6 y54 ff3 fs2 fc0 sc0 ls0 ws0">public Internet. Many of these data centers are located in, or close to, lower tier ISPs. </div><div class="t m0 x5 h6 y55 ff3 fs2 fc0 sc0 ls0 ws0">Therefore, when Google delivers content to a user, it often can bypass higher tier ISPs. </div><div class="t m0 x5 h6 y56 ff3 fs2 fc0 sc0 ls0 ws0">What motivates content providers to create these networks? First, the content provider </div><div class="t m0 x5 h6 y57 ff3 fs2 fc0 sc0 ls0 ws0">has more control over the user experience, since it has to use few intermediary ISPs. </div><div class="t m0 x5 h6 y58 ff3 fs2 fc0 sc0 ls0 ws0">Second, it can save money by sending less traffic into provider networks. Third, if ISPs </div><div class="t m0 x5 h6 y59 ff3 fs2 fc0 sc0 ls0 ws0">decide to charge more money to highly profitable content providers (in countries where </div><div class="t m0 x5 h6 y5a ff3 fs2 fc0 sc0 ls0 ws0">net neutrality doesn't apply), the content providers can avoid these extra payments. </div><div class="t m0 x4 h6 y5b ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x4 h6 y5c ff3 fs2 fc0 sc0 ls0 ws0">16. The delay components are processing delays, transmission delays, propagation delays, </div><div class="t m0 x5 h6 y5d ff3 fs2 fc0 sc0 ls0 ws0">and queuing delays. All of these delays are fixed, except for the queuing delays, which </div><div class="t m0 x5 h6 y5e ff3 fs2 fc0 sc0 ls0 ws0">are variable. </div><div class="t m0 x4 h6 y5f ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="c x1 y2b w4 ha"><div class="t m0 x0 hb y2c ff5 fs4 fc0 sc0 ls0 ws0">© 2020 Pearson Education, Hoboken, NJ. All rights reserved.</div></div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div><div id="pf4" class="pf w0 h0" data-page-no="4"><div class="pc pc4 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/87768255/bg4.jpg"><div class="t m0 x4 h6 y2f ff3 fs2 fc0 sc0 ls0 ws0">17. a) 1000 km, 1 Mbps, 100 bytes</div><div class="t m0 x5 h6 y31 ff3 fs2 fc0 sc0 ls0 ws0">b) 100 km, 1 Mbps, 100 bytes</div><div class="t m0 x4 h6 y34 ff3 fs2 fc0 sc0 ls0 ws0">18. 10msec; d/s; no; no</div><div class="t m0 x4 h6 y36 ff3 fs2 fc0 sc0 ls0 ws0">19. a) 500 kbps</div><div class="t m0 x5 h6 y37 ff3 fs2 fc0 sc0 ls0 ws0">b) 64 seconds</div><div class="t m0 x5 h6 y38 ff3 fs2 fc0 sc0 ls5 ws0">c) 100kbps; 320 seconds</div><div class="t m0 x4 h6 y3a ff3 fs2 fc0 sc0 ls0 ws0">20. End system A breaks the large file into chunks. It adds header to each chunk, thereby</div><div class="t m0 x5 h6 y3b ff3 fs2 fc0 sc0 ls0 ws0">generating multiple packets from the file. The header in each packet includes the IP</div><div class="t m0 x5 h6 y3c ff3 fs2 fc0 sc0 ls0 ws0">address of the destination (end system B). The packet switch uses the destination IP</div><div class="t m0 x5 h6 y3d ff3 fs2 fc0 sc0 ls0 ws0">address in the packet to determine the outgoing link. Asking which road to take is</div><div class="t m0 x5 h6 y3e ff3 fs2 fc0 sc0 ls0 ws0">analogous to a packet asking which outgoing link it should be forwarded on, given the</div><div class="t m0 x5 h6 y3f ff3 fs2 fc0 sc0 ls0 ws0">packet’s destination address.</div><div class="t m0 x4 h6 y41 ff3 fs2 fc0 sc0 ls0 ws0">21. The maximum emission rate is 500 packets/sec and the maximum transmission rate is</div><div class="t m0 x1d hd y42 ff3 fs2 fc0 sc0 ls0 ws0">350 packets/sec. The corresponding traffic intensity is 500/350 =1.43 > 1. Loss will</div><div class="t m0 x1d hd y60 ff3 fs2 fc0 sc0 ls0 ws0">eventually occur for each experiment; but the time when loss first occurs will be</div><div class="t m0 x1d h6 y61 ff3 fs2 fc0 sc0 ls0 ws0">different from one experiment to the next due to the randomness in the emission</div><div class="t m0 x1d h6 y62 ff3 fs2 fc0 sc0 ls0 ws0">process.</div><div class="t m0 x4 h6 y63 ff3 fs2 fc0 sc0 ls0 ws0">22. Five generic tasks are error control, flow control, segmentation and reassembly,</div><div class="t m0 x5 h6 y64 ff3 fs2 fc0 sc0 ls0 ws0">multiplexing, and connection setup. Yes, these tasks can be duplicated at different</div><div class="t m0 x5 h6 y65 ff3 fs2 fc0 sc0 ls0 ws0">layers. For example, error control is often provided at more than one layer.</div><div class="t m0 x4 h6 y66 ff3 fs2 fc0 sc0 ls0 ws0">23. The five layers in the Internet protocol stack are – from top to bottom – the application</div><div class="t m0 x5 h6 y67 ff3 fs2 fc0 sc0 ls0 ws0">layer, the transport layer, the network layer, the link layer, and the physical layer. The</div><div class="t m0 x5 h6 y68 ff3 fs2 fc0 sc0 ls0 ws0">principal responsibilities are outlined in Section 1.5.1.</div><div class="t m0 x4 h6 y69 ff3 fs2 fc0 sc0 ls0 ws0">24. Application-layer message: data which an application wants to send and passed onto</div><div class="t m0 x5 h6 y6a ff3 fs2 fc0 sc0 ls0 ws0">the transport layer; transport-layer segment: generated by the transport layer and</div><div class="t m0 x5 h6 y6b ff3 fs2 fc0 sc0 ls0 ws0">encapsulates application-layer message with transport layer header; network-layer</div><div class="t m0 x5 h6 y6c ff3 fs2 fc0 sc0 ls0 ws0">datagram: encapsulates transport-layer segment with a network-layer header; link-layer</div><div class="t m0 x5 h6 y6d ff3 fs2 fc0 sc0 ls0 ws0">frame: encapsulates network-layer datagram with a link-layer header.</div><div class="t m0 x4 h6 y6e ff3 fs2 fc0 sc0 ls0 ws0">25. Routers process network, link and physical layers (layers 1 through 3). (This is a little</div><div class="t m0 x5 h6 y6f ff3 fs2 fc0 sc0 ls0 ws0">bit of a white lie, as modern routers sometimes act as firewalls or caching components,</div><div class="t m0 x5 h6 y70 ff3 fs2 fc0 sc0 ls0 ws0">and process Transport layer as well.) Link layer switches process link and physical</div><div class="t m0 x5 h6 y71 ff3 fs2 fc0 sc0 ls0 ws0">layers (layers 1 through2). Hosts process all five layers.</div><div class="t m0 x1e h6 y72 ff3 fs2 fc0 sc0 ls0 ws0">26. A self-replicating malware is a piece of code that cab enter and infect our devices,</div><div class="t m0 x1f h6 y73 ff3 fs2 fc0 sc0 ls0 ws0">and once it infects the host, from that host it seeks entry into other hosts over the Internet. </div><div class="t m0 x4 h6 y74 ff3 fs2 fc0 sc0 ls0 ws0">27. Creation of a botnet requires an attacker to find vulnerability in some application or</div><div class="t m0 x20 h6 y75 ff3 fs2 fc0 sc0 ls0 ws0">system (e.g. exploiting the buffer overflow vulnerability that might exist in an</div><div class="t m0 x20 h6 y76 ff3 fs2 fc0 sc0 ls0 ws0">application). After finding the vulnerability, the attacker needs to scan for hosts that</div><div class="t m0 x20 h6 y77 ff3 fs2 fc0 sc0 ls0 ws0">are vulnerable. The target is basically to compromise a series of systems by exploiting</div><div class="c x1 y2b w4 ha"><div class="t m0 x0 hb y2c ff5 fs4 fc0 sc0 ls0 ws0">© 2020 Pearson Education, Hoboken, NJ. All rights reserved.</div></div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div><div id="pf5" class="pf w0 h0" data-page-no="5"><div class="pc pc5 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/87768255/bg5.jpg"><div class="c x2 y3 w3 h4"><div class="t m0 x3 hc y2d ff6 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x3 hc y2e ff6 fs2 fc0 sc0 ls0 ws0"> </div></div><div class="t m0 x20 h6 y2f ff3 fs2 fc0 sc0 ls0 ws0">that particular vulnerability. Any system that is part of the botnet can automatically </div><div class="t m0 x20 h6 y31 ff3 fs2 fc0 sc0 ls6 ws0">scan its environment and propagate by exploiting the vulnerability. An important </div><div class="t m0 x20 h6 y32 ff3 fs2 fc0 sc0 ls0 ws0">property of such botnets is that the originator of the botnet can remotely control and </div><div class="t m0 x20 h6 y34 ff3 fs2 fc0 sc0 ls0 ws0">issue commands to all the nodes in the botnet. Hence, it becomes possible for the </div><div class="t m0 x20 h6 y35 ff3 fs2 fc0 sc0 ls0 ws0">attacker to issue a command to all the nodes, that target a single node (for example, </div><div class="t m0 x20 h6 y36 ff3 fs2 fc0 sc0 ls5 ws0">all nodes in the botnet might be commanded by the attacker to send a TCP SYN </div><div class="t m0 x20 h6 y37 ff3 fs2 fc0 sc0 ls0 ws0">message to the target, which might result in a TCP SYN flood attack at the target). </div><div class="t m0 x4 h6 y38 ff3 fs2 fc0 sc0 ls0 ws0"> </div><div class="t m0 x4 h6 y39 ff3 fs2 fc0 sc0 ls0 ws0">28. Trudy can pretend to be Bob to Alice (and vice-versa) and partially or completely </div><div class="t m0 x5 h6 y3a ff3 fs2 fc0 sc0 ls0 ws0">modify the message(s) being sent from Bob to Alice. For example, she can easily </div><div class="t m0 x5 h6 y3b ff3 fs2 fc0 sc0 ls0 ws0">change the phrase “Alice, I owe you $1000” to “Alice, I owe you $10,000”. </div><div class="t m0 x5 h6 y3c ff3 fs2 fc0 sc0 ls0 ws0">Furthermore, Trudy can even drop the packets that are being sent by Bob to Alice (and </div><div class="t m0 x5 h6 y3d ff3 fs2 fc0 sc0 ls0 ws0">vise-versa), even if the packets from Bob to Alice are encrypted. </div><div class="c x1 y2b w4 ha"><div class="t m0 x0 hb y2c ff5 fs4 fc0 sc0 ls0 ws0">© 2020 Pearson Education, Hoboken, NJ. All rights reserved.</div></div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div>

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