25.02.2013 Views

TCP/IP Tutorial and Technical Overview - IBM Redbooks

TCP/IP Tutorial and Technical Overview - IBM Redbooks

TCP/IP Tutorial and Technical Overview - IBM Redbooks

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Question section<br />

The next section contains the queries for the name server. It contains QDcount<br />

(usually 1) entries, each in the format shown in Figure 12-6.<br />

Figure 12-6 DNS question format 2<br />

Where:<br />

Length A single byte giving the length of the next label.<br />

Label One element of the domain name characters (for example, ibm<br />

from ral.ibm.com). The domain name referred to by the question is<br />

stored as a series of these variable length labels, each preceded<br />

by a 1-byte length.<br />

00 X'00' indicates the end of the domain name <strong>and</strong> represents the null<br />

label of the root domain.<br />

Type 2 bytes specifying the type of query. It can have any value from the<br />

Type field in a resource record.<br />

Class 2 bytes specifying the class of the query. For Internet queries, this<br />

will be IN.<br />

2 Note that all of the fields are byte-aligned. The alignment of the Type field on a 4-byte boundary is<br />

for example purposes <strong>and</strong> is not required by the format.<br />

442 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!