Syngress - Eleventh Hour Network+ Exam N10-004 Study Guide (11 ...

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174 CHAPTER 10 Network Troubleshooting 5. Your e-mail server is having network connectivity problems. You have replaced the NIC and reconfigured the IP address. The last step that you take is to start the e-mail services, and all services have now started successfully without generating error messages. Which of the following actions will allow you to verify that the e-mail services are successfully accepting inbound e-mail A. Telnet from a client machine to port 25 on the e-mail server B. Telnet from a client machine to port 23 on the e-mail server C. Use POP3 to create an e-mail queue and validate that e-mail passes through it successfully D. Use IMAP4 to send Internet e-mail to the server Answers 1. Correct answers and explanations: A and B. Answer A is correct because when a router is down it is possible that a Request timed out can be the response listed. Answer B is correct because if a router is configured not to respond to ping attempts, Request timed out will be displayed and none of the routers which should receive the packets after that one will get them. When a tracert command is issued, a ping is being sent to each hop along the route. If ping is blocked by a specific router, then no response is received and the request will time out resulting in the Request timed out displayed above. Incorrect answers and explanations: C and D. Answer C is incorrect because the next hop is not determined by DNS resolution. The next hop is determined by the previous hop. If a router is misconfigured, the wrong path can take place, but this would not be attributed to DNS. Answer D is incorrect, because the maximum hop count is 30, and tracert simply ends when it reaches the maximum hop count. It does not display Request timed out when the maximum hop count is reached. 2. Correct Answers & Explanations: B. Answer B is correct, because the workstation is displaying a 169.254.1.96 IP address, which is an APIPA address. APIPA is short for Automatic Private IP Address and covers a range of 169.254.0.0 through 169.254.255.254. An address from this range is automatically assigned to a machine when it is configured to utilize DHCP, but it is not able to contact a DHCP server. Typically when a machine is assigned an APIPA address it is not able to connect to with the rest of the network, since the rest of the network will most likely be utilizing a different addressing scheme. In very small business networks and home network environment is it possible to rely on APIPA for addressing. APIPA does not configure variables such as a gateway, so in most corporate environments where routers exist APIPA isn’t appropriate for network configurations. Incorrect Answers & Explanations: A, C, and D. Answer A is incorrect, because a default gateway is never configured when an APIPA address has been assigned. Answer C is incorrect, because the workstation does not have a gateway value configured; it has an APIPA address configured,
Troubleshooting the Application Layer 175 which never has an accompanying gateway value. Answer D is incorrect, because when a workstation’s DHCP lease has expired it will attempt to renew its existing IP address. It is only is if is unsuccessful in renewal that it will be forced to abandon the currently issued IP address. It will then issue an APIPA address instead. 3. Correct answers and explanations: A and C. Answer A is correct because by changing the configuration to obtain an IP address automatically, the machine will connect to the DHCP server to receive an IP address and also receive the configured options which include the new default gateway value. Answer C is correct because by manually updating the IP address of the default gateway on the client machine, it will be able to connect to the correct default gateway. Incorrect answers and explanations: B and D. Answer B is incorrect because an ipconfig/renew command will force a client to attempt renewal of its DHCP address. Since this client machine is configured with a static IP address, issuing this command will not have an effect, and will not cause the client machine to receive the correct default gateway from the DHCP server. Answer D is incorrect because ipconfig/release command will force a client to release its current DHCP address. Since this client machine is configured with a static IP address, issuing this command will not have an effect and will not cause the client machine to release a DHCP address since it doesn’t have one. Also, since it is configured with a static IP address, this command will not cause the client to receive the correct default gateway from the DHCP server. 4. Correct answers and explanations: A. Answer A is correct because ports 20 and 21 are used for FTP traffic. By configuring the firewall to allow FTP traffic to pass through, the user will be able to transfer the files required successfully. Incorrect answers and explanations: B, C, and D. Answer B is incorrect because ports 25 and <strong>11</strong>0 are not utilized for FTP. Port 25 is utilized by SMTP and <strong>11</strong>0 is utilized by POP3. Answer C is incorrect because allowing all TCP traffic to the user’s workstation when only FTP is required is an unnecessary change, which leaves the machine vulnerable. Answer D is incorrect because ports 80 and 443 are not utilized for FTP. Port 80 is utilized by HTTP and port 443 is utilized by Secure HTTP (HTTPS). 5. Correct answers and explanations: A. Answer A is correct because by the telnet command can be used to verify that a port on a particular machine is open. Issuing the telnet command on port 25 will validate that the SMTP services which are responsible for inbound e-mail are up and functioning. Incorrect answers and explanations: B, C, and D. Answer B is incorrect because port 23 is the default telnet port and you cannot determine if e-mail services are functioning correctly by telenetting to port 23. Answer C is incorrect because POP3 is a protocol used to receive e-mail from server to a client. It is not used to create or validate queue. Answer D is incorrect because IMAP4 is a protocol used to receive e-mail from server to a client.
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