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Unformatted text preview: re is a significant pause between typing the Telnet command and printing the IP address, this delay is caused by
the resolver contacting a name server to resolve the name into an IP address. A pause between printing Trying and
Connected to, however, is a delay caused by the establishment of the TCP connection between the client and
server, not the DNS. 14.5 Pointer Queries
A perpetual stumbling block in understanding the DNS is how pointer queries are handled - given an IP address, return
the name (or names) corresponding to that address.
First return to Figure 14.1 and examine the arpa top-level domain, and the in-addr domain beneath it. When an
organization joins the Internet and obtains authority for a portion of the DNS name space, such as noao.edu, they
also obtain authority for a portion of the in-addr.arpa name space corresponding to their IP address on the
Internet. In the case of noao.edu it is the class B network ID 140.252. The level of the DNS tree beneath inaddr.arpa must be the first byte of the IP address (140 in this example), the next level is the next byte of the IP
address (252), and so on. But remember that names are written starting at the bottom of the DNS tree, working upward.
This means the DNS name for the host sun, with an IP address of 220.127.116.11, is 18.104.22.168. in-addr.arpa.
We have to write the 4 bytes of the IP address backward because authority is delegated based on network IDs: the first file:///D|/Documents%20and%20Settings/bigini/Docu.../homenet2run/tcpip/tcp-ip-illustrated/dns_the.htm (10 of 18) [12/09/2001 14.47.06] Chapter 14. DNS: The Domain Name System byte of a class A address, the first and second bytes of a class B address, and the first, second, and third bytes of a class
C address. The first byte of the IP address must be immediately below the in-addr label, but FQDNs are written
from the bottom of the tree up. If FQDNs were written from the top down, then the DNS name for the IP address would
be arpa.in-addr.22.214.171.124, but the...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12