Upper Layer Protocols App Seasons and Utilities

This subsecsiou covere applihhtions such as telne t, FTP, TFTP, SMTP, POP3, D NS, SNMP, RIP, HTTP, HTTPS, and DHCP. Obviously, these are not the only applications you will need to troubleshoot| but they are very 3ommon.

First look at the tr;rmint^| emulation protocol telnet. from an aieplication perspective. Review Figurea 3-9 and 3-1 0 and your Smffer capture flo (shape 3 telnet from ho/Ca to n1 sniffer capture)^gure 3-14 illus-rates the tdinet xession from hosta on port 1079 to r1 on port 23. Line 10 starts the telnet session, which was dependent on the TCP 3-way handshake in lines 7, 8, and 9. Notipe tha echo, w indow size, and terminal negotia tion in li nes 10 to 15 . i^ame g2 is waiting for the logm that eventually appears in lines 17 to 25 one character at a time. In addition, notice how that after the user-level password I typed the necessary command and password to get into enable mode. Although I do not show all this in the screen capture of Figure 3-14, if you have your own file you can see the rest of the commands that were typed on the router, letter for letter. It is pretty obvious here that the standard telnet programs do not encrypt the login information, and I doubt that this is what you want people to see when you telnet to your devices to configure them. In the real-world application of telnet where security is more of a concern, many people use secure telnet programs (Se cute Shelt [SS H] port 22n. Exam ples mclude Se crreCST| CommNet| an d PuNPh^SSH.

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