tyt11fi.htm

快速学习TCP/IP协议

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<P>8

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<P>MG

<BR>

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<P>Mailbox member

<BR>

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<P>9

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<P>MR

<BR>

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<P>Mail rename domain

<BR>

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<P>10

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<P>NULL

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<P>Null resource record

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<P>11

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<P>WKS

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>Well-known service

<BR>

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<P>12

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<P>PTR

<BR>

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<P>Pointer to a domain name

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<P>13

<BR>

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<P>HINFO

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>Host information

<BR>

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<P>14

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>MINFO

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>Mailbox information

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>15

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>MX

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>Mail exchange

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>16

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>TXT

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<P>Text strings

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<P>17

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>RP

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>Responsible person

<BR>

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<TR>

<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>18

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>AFSDB

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>AFS-type services

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>19

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>X.25

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>X.25 address

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<P>20

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>ISDN

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>ISDN address

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>21

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>RT

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>Route through</FONT>

</TABLE></CENTER><BR>

<P>The Class field in the resource record layout contains a value for the class of record. If no value is specified, the last class used is substituted. Internet name servers usually have the code IN.

<BR>

<P>The Time to Live (TTL) field specifies the amount of time in seconds that the resource record is valid in the cache. If a value of 0 is used, the record should not be added to the cache. If the TTL field is omitted, a default value is used. Usually this field tells the name server how long the entry is valid before it has to ask for an update.

<BR>

<P>The data section of the resource record contains two parts, consisting of the length of the record and the data itself. The Data Length field specifies the length of the data section. The data is a variable-length field (hence the need for a length value) that describes the entry somehow. The use of this field differs with the different types of resource records.

<BR>

<P>Some resource record types have a single piece of information in the data area, such as an address, or at most three pieces of information. The only exception is the Start of Authority resource record. The contents of the resource record data areas (except SOAs) are given in Table 11.2.

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<BR>

<P ALIGN=CENTER>

<CENTER>

<FONT COLOR="#000080"><B>Table 11.2. The contents of the resource record data areas.</B></FONT></CENTER>

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<CENTER><TABLE  BORDERCOLOR=#000040 BORDER=1 CELLSPACING=2 CELLPADDING=3 >

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<P><B><I>RR Type</I></B>

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<P><B><I>Fields in Data Area</I></B>

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<TR>

<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>A

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<P>Address: A network address

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<P>NS

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<P>NSDNAME: The domain name of host

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>MG

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>MGNAME: The domain name of mailbox

<BR>

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<TR>

<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>CNAME

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>CNAME: An alias for the machine

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>HINFO

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>CPU: A string identifying CPU type

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080><BR></FONT>

</TD>

<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>OS: A string identifying operating system

<BR>

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>MINFO

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<TD BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<P>RMAILBX: A mailbox responsible for mailing lists

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