表1 IP头字段解释 字段长度含义Version4比特

讯享网

<ul><li>4&#xff1a;表示为IPV4&#xff1b;</li><li>6&#xff1a;表示为IPV6。</li></ul></td></tr><tr><td style="vertical-align:top;">IHL</td><td style="vertical-align:top;">4比特</td><td style="vertical-align:top;">首部长度&#xff0c;如果不带Option字段&#xff0c;则为20&#xff0c;最长为60&#xff0c;该值限制了记录路由选项。以4字节为一个单位。</td></tr><tr><td style="vertical-align:top;">Type of Service</td><td style="vertical-align:top;">8比特</td><td style="vertical-align:top;">服务类型。只有在有QoS差分服务要求时这个字段才起作用。</td></tr><tr><td style="vertical-align:top;">Total Length</td><td style="vertical-align:top;">16比特</td><td style="vertical-align:top;">总长度&#xff0c;整个IP数据报的长度&#xff0c;包括首部和数据之和&#xff0c;单位为字节&#xff0c;最长65535&#xff0c;总长度必须不超过最大传输单元MTU。</td></tr><tr><td style="vertical-align:top;">Identification</td><td style="vertical-align:top;">16比特</td><td style="vertical-align:top;">标识&#xff0c;主机每发一个报文&#xff0c;加1&#xff0c;分片重组时会用到该字段。</td></tr><tr><td style="vertical-align:top;">Flags</td><td style="vertical-align:top;">3比特</td><td style="vertical-align:top;">标志位&#xff1a; <p><strong>图2 </strong>IP Flag字段格式</p> <p><img alt="" height="78" src="https://i-blog.csdnimg.cn/blog_migrate/fd8e4acefbda0f8f89fdca3d.png" width="181" /></p> <ul><li>Bit 0: 保留位&#xff0c;必须为0。</li><li>Bit 1: DF&#xff08;Don&#39;t Fragment&#xff09;&#xff0c;能否分片位&#xff0c;0表示可以分片&#xff0c;1表示不能分片。</li><li>Bit 2: MF&#xff08;More Fragment&#xff09;&#xff0c;表示是否该报文为最后一片&#xff0c;0表示最后一片&#xff0c;1代表后面还有。</li></ul></td></tr><tr><td style="vertical-align:top;">Fragment Offset</td><td style="vertical-align:top;">12比特</td><td style="vertical-align:top;">片偏移&#xff1a;分片重组时会用到该字段。表示较长的分组在分片后&#xff0c;某片在原分组中的相对位置。以8个字节为偏移单位。</td></tr><tr><td style="vertical-align:top;">Time to Live</td><td style="vertical-align:top;">8比特</td><td style="vertical-align:top;">生存时间&#xff1a;可经过的最多路由数&#xff0c;即数据包在网络中可通过的路由器数的最大值。</td></tr><tr><td style="vertical-align:top;">Protocol</td><td style="vertical-align:top;">8比特</td><td style="vertical-align:top;"> <p>协议&#xff1a;下一层协议。指出此数据包携带的数据使用何种协议&#xff0c;以便目的主机的IP层将数据部分上交给哪个进程处理。</p> <p>常见值&#xff1a;</p> <ul><li>0: 保留Reserved</li><li>1: ICMP, Internet Control Message [RFC792]</li><li>2: IGMP, Internet Group Management [RFC1112]</li><li>3: GGP, Gateway-to-Gateway [RFC823]</li><li>4: IP in IP (encapsulation) [RFC2003]</li><li>6: TCP Transmission Control Protocol [RFC793]</li><li>17: UDP User Datagram Protocol [RFC768]</li><li>20: HMP Host Monitoring Protocol [RFC 869]</li><li>27: RDP Reliable Data Protocol [ RFC908 ]</li><li>46: RSVP (Reservation Protocol)</li><li>47: GRE (General Routing Encapsulation)</li><li>50: ESP Encap Security Payload [RFC2406]</li><li>51: AH (Authentication Header) [RFC2402]</li><li>54: NARP (NBMA Address Resolution Protocol) [RFC1735]</li><li>58: IPv6-ICMP (ICMP for IPv6) [RFC1883]</li><li>59: IPv6-NoNxt (No Next Header for IPv6) [RFC1883]</li><li>60: IPv6-Opts (Destination Options for IPv6) [RFC1883]</li><li>89: OSPF (OSPF Version 2) [RFC 1583]</li><li>112: VRRP (Virtual Router Redundancy Protocol) [RFC3768]</li><li>115: L2TP (Layer Two Tunneling Protocol)</li><li>124: ISIS over IPv4</li><li>126: CRTP (Combat Radio Transport Protocol)</li><li>127: CRUDP (Combat Radio User Protocol)</li><li>132: SCTP (Stream Control Transmission Protocol)</li><li>136: UDPLite [RFC 3828]</li><li>137: MPLS-in-IP [RFC 4023]</li></ul></td></tr><tr><td style="vertical-align:top;">Header Checksum</td><td style="vertical-align:top;">16比特</td><td style="vertical-align:top;">首部检验和&#xff0c;只检验数据包的首部&#xff0c;不检验数据部分。这里不采用CRC检验码&#xff0c;而采用简单的计算方法。</td></tr><tr><td style="vertical-align:top;">Source Address</td><td style="vertical-align:top;">32比特</td><td style="vertical-align:top;">源IP地址。</td></tr><tr><td style="vertical-align:top;">Destination Address</td><td style="vertical-align:top;">32比特</td><td style="vertical-align:top;">目的IP地址。</td></tr><tr><td style="vertical-align:top;">Options</td><td style="vertical-align:top;">可变</td><td style="vertical-align:top;">选项字段&#xff0c;用来支持排错&#xff0c;测量以及安全等措施&#xff0c;内容丰富&#xff08;请参见下表&#xff09;。选项字段长度可变&#xff0c;从1字节到40字节不等&#xff0c;取决于所选项的功能。</td></tr><tr><td style="vertical-align:top;">Padding</td><td style="vertical-align:top;">可变</td><td style="vertical-align:top;">填充字段&#xff0c;全填0。</td></tr></tbody>