TCP IP Illustrated

In section 145 we talked about pointer queries in the

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Unformatted text preview: pivl.errata.Z 105 bytes received in 4.1 seconds (0.83 Kbytes/s) ftp> quit 221 Goodbye. sun % uncompress stevens.tcpipivl.errata.Z sun % more stevens.tcpipivl.errata The uncompress is because many files available for anonymous FTP are compressed file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (21 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol using the Unix compress(l) program, resulting in a file extension of .Z. These files must be transferred using the binary file type, not the ASCII file type. Anonymous FTP from an Unknown IP Address We can tie together some features of routing and the Domain Name System using anonymous FTP. In Section 14.5 we talked about pointer queries in the DNS - taking an IP address and returning the hostname. Unfortunately not all system administrators set up their name servers correctly with regard to pointer queries. They often add new hosts to the file required for name-to-address mapping, but forget to add them to the file for address-to-name mapping. We often see this with traceroute, when it prints an IP address instead of a hostname. Some anonymous FTP servers require that the client have a valid domain name. This allows the server to log the domain name of the host that's doing the transfer. Since the only client identification the server receives in the IP datagram from the client is the IP address of the client, the server can call the DNS to do a pointer query, and obtain the domain name of the client. If the name server responsible for the client host is not set up correctly, this pointer query can fail. To see this error we'll do the following steps. 1. Change the IP address of our host slip (see the figure on the inside front cover) to This is a valid IP address for the author's subnet, but not entered into the name server for the domain. 2. Change the destination IP address of the SLIP link on bsdi to 3. Add a ro...
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