网络服务-DHCP

秒速五厘米 2022-01-05 09:57 384阅读 0赞

# 1.DHCP简介 #

DHCP（Dynamtic Host Configuraton Protocol，动态主机配置协议）是一个工作在应用层的**局域网网络协议**，数据传输时使用UDP不可靠谱传输协议工作，通常被应用在大型的局域网络环境中，主要作用是集中的管理、分配网络资源，使网络环境中的主机能动态的获得IP地址、Gatway地址、DNS服务器地址等信息，能够提升地址的使用率。

# 2.DHCP工作原理（租约四部曲+续租） #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70]  
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# 3.DHCP 服务搭建 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 5]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 6]

# 4.DHCP实验部署 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 7]  
**具体实验操作：**  
1.修改配置文件dhcpd.conf ，将其中前几个不用的subnet注释掉；  
2.设置一个subnet要分配的网段和子网掩码，声明可用的IP地址，其余用不到的可以暂时不设置；  
3.保留最小租约时间和最大租约时间；

[root@oracle dhcp]# vim dhcpd.conf
    # dhcpd.conf
    #
    # Sample configuration file for ISC dhcpd
    #
    
    # option definitions common to all supported networks...
    option domain-name "example.org";
    option domain-name-servers ns1.example.org, ns2.example.org;
    
    default-lease-time 600;
    max-lease-time 7200;
    
    # Use this to enble / disable dynamic dns updates globally.
    #ddns-update-style none;
    
    # If this DHCP server is the official DHCP server for the local
    # network, the authoritative directive should be uncommented.
    #authoritative;
    
    # Use this to send dhcp log messages to a different log file (you also
    # have to hack syslog.conf to complete the redirection).
    log-facility local7;
    
    # No service will be given on this subnet, but declaring it helps the 
    # DHCP server to understand the network topology.
    
    #subnet 10.152.187.0 netmask 255.255.255.0 {
    #}
    
    # This is a very basic subnet declaration.
    
    #subnet 10.254.239.0 netmask 255.255.255.224 {
    #  range 10.254.239.10 10.254.239.20;
    #  option routers rtr-239-0-1.example.org, rtr-239-0-2.example.org;
    #}
    
    # This declaration allows BOOTP clients to get dynamic addresses,
    # which we don't really recommend.
    
    #subnet 10.254.239.32 netmask 255.255.255.224 {
    #  range dynamic-bootp 10.254.239.40 10.254.239.60;
    #  option broadcast-address 10.254.239.31;
    #  option routers rtr-239-32-1.example.org;
    #}
    
    # A slightly different configuration for an internal subnet.
    subnet 192.168.197.0 netmask 255.255.255.0 {
      range 192.168.197.20 192.168.197.200;
    #  option domain-name-servers ns1.internal.example.org;
    #  option domain-name "internal.example.org";
    #  option routers 10.5.5.1;
    #  option broadcast-address 10.5.5.31;
      default-lease-time 600;
      max-lease-time 7200;
    }

4.启动服务，service dhcpd start  
5.查看是否启动成功

[root@oracle dhcp]# service dhcpd start
    Starting dhcpd:                                            [  OK  ]
    [root@oracle dhcp]# netstat -tluna     
    Active Internet connections (servers and established)
    Proto Recv-Q Send-Q Local Address               Foreign Address             State      
    tcp        0      0 0.0.0.0:55647               0.0.0.0:*                   LISTEN      
    tcp        0      0 0.0.0.0:111                 0.0.0.0:*                   LISTEN      
    tcp        0      0 0.0.0.0:21                  0.0.0.0:*                   LISTEN      
    tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN      
    tcp        0      0 127.0.0.1:631               0.0.0.0:*                   LISTEN      
    tcp        0      0 127.0.0.1:25                0.0.0.0:*                   LISTEN      
    tcp        0      0 192.168.197.134:22          192.168.197.1:58794         ESTABLISHED 
    tcp        0      0 192.168.197.134:22          192.168.197.1:60712         ESTABLISHED 
    tcp        0      0 192.168.197.134:22          192.168.197.135:63025       ESTABLISHED 
    tcp        0      0 :::51618                    :::*                        LISTEN      
    tcp        0      0 :::33060                    :::*                        LISTEN      
    tcp        0      0 :::3306                     :::*                        LISTEN      
    tcp        0      0 :::111                      :::*                        LISTEN      
    tcp        0      0 :::22                       :::*                        LISTEN      
    tcp        0      0 ::1:631                     :::*                        LISTEN      
    tcp        0      0 ::1:25                      :::*                        LISTEN      
    udp        0      0 127.0.0.1:1001              0.0.0.0:*                               
    udp        0      0 0.0.0.0:111                 0.0.0.0:*                               
    udp        0      0 0.0.0.0:631                 0.0.0.0:*                               
    udp        0      0 0.0.0.0:24840               0.0.0.0:*                               
    udp        0      0 0.0.0.0:67                  0.0.0.0:*                               
    udp        0      0 0.0.0.0:838                 0.0.0.0:*                               
    udp        0      0 :::111                      :::*                                    
    udp        0      0 :::36291                    :::*                                    
    udp        0      0 :::838                      :::*

6.验证，将局域网内的另外一台主机B，ip获取方式改成DHCP  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 8]  
7.重启另一台主机B的网卡，service network restart (该命令会重启所有网卡，如果怕影响别的网卡服务，可以使用下面这条语句，只启动特定的网卡)

[root@135 ~]# ifdown eth0;ifup eth0

验证主机B，通过DHCP服务来获取IP的新ip地址（之前是静态设置的ip135,现在变成了129）

[root@135 Desktop]# ifconfig
    eth0      Link encap:Ethernet  HWaddr 00:0C:29:C1:E2:78  
              inet addr:192.168.197.129  Bcast:192.168.197.255  Mask:255.255.255.0
              inet6 addr: fe80::20c:29ff:fec1:e278/64 Scope:Link
              UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
              RX packets:12562 errors:0 dropped:0 overruns:0 frame:0
              TX packets:12696 errors:0 dropped:0 overruns:0 carrier:0
              collisions:0 txqueuelen:1000 
              RX bytes:1132479 (1.0 MiB)  TX bytes:1389920 (1.3 MiB)
    
    lo        Link encap:Local Loopback  
              inet addr:127.0.0.1  Mask:255.0.0.0
              inet6 addr: ::1/128 Scope:Host
              UP LOOPBACK RUNNING  MTU:65536  Metric:1
              RX packets:5784 errors:0 dropped:0 overruns:0 frame:0
              TX packets:5784 errors:0 dropped:0 overruns:0 carrier:0
              collisions:0 txqueuelen:0 
              RX bytes:522236 (509.9 KiB)  TX bytes:522236 (509.9 KiB)

8.回到搭建有DHCP服务的主机A上，查看DHCP的服务日志/var/log/messages，进一步了解，DHCP的工作原理（即租约四部曲）。

[root@oracle dhcp]# tail -10 /var/log/messages
    Jun 23 06:56:49 oracle dhcpd: Wrote 0 leases to leases file.
    Jun 23 06:56:49 oracle dhcpd: Listening on LPF/eth0/00:0c:29:64:b4:6d/192.168.197.0/24
    Jun 23 06:56:49 oracle dhcpd: Sending on   LPF/eth0/00:0c:29:64:b4:6d/192.168.197.0/24
    Jun 23 06:56:49 oracle dhcpd: Sending on   Socket/fallback/fallback-net
    Jun 23 07:00:31 oracle dhcpd: DHCPDISCOVER from 00:0c:29:c1:e2:78 via eth0
    Jun 23 07:00:31 oracle dhcpd: ns1.example.org: temporary name server failure
    Jun 23 07:00:31 oracle dhcpd: ns2.example.org: temporary name server failure
    Jun 23 07:00:31 oracle dhcpd: DHCPOFFER on 192.168.197.129 to 00:0c:29:c1:e2:78 (135) via eth0
    Jun 23 07:00:31 oracle dhcpd: DHCPREQUEST for 192.168.197.129 (192.168.197.134) from 00:0c:29:c1:e2:78 (135) via eth0
    Jun 23 07:00:31 oracle dhcpd: DHCPACK on 192.168.197.129 to 00:0c:29:c1:e2:78 (135) via eth0

获取请求：MAC地址为00:0c:29:c1:e2:78的主机发出来的

Jun 23 07:00:31 oracle dhcpd: DHCPDISCOVER from 00:0c:29:c1:e2:78 via eth0

向客户机B发送OFFER

Jun 23 07:00:31 oracle dhcpd: DHCPOFFER on 192.168.197.129 to 00:0c:29:c1:e2:78 (135) via eth0

收到来自客户机B的确认IP消息DHCPREQUEST

Jun 23 07:00:31 oracle dhcpd: DHCPREQUEST for 192.168.197.129 (192.168.197.134) from 00:0c:29:c1:e2:78 (135) via eth0

发送给客户机B的最终租约确认

Jun 23 07:00:31 oracle dhcpd: DHCPACK on 192.168.197.129 to 00:0c:29:c1:e2:78 (135) via eth0

## 4.2.DHCP的地址保留实验（固定地址分配） ##

目的：使得客户机B每次利用DHCP服务获取的IP地址是一样的，保持不变的IP  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 9]  
**修改配置文件：/etc/dhcp/dhcpd.conf**  
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**重启DHCPD服务** ：**service dhcpd restart**

[root@oracle dhcp]# service dhcpd restart
    Shutting down dhcpd:                                       [  OK  ]
    Starting dhcpd:                                            [  OK  ]

**在客户机上执行** **：ifdown eth0;ifup eth0** 重启eth0网卡，检查IP地址  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 11]

## 4.3超级作用域（同一局域网） ##

当局域网的主机台数超过一个网段的台数时，多于255了，需要在不改变为B类网段的情况下，添加主机台数，和之前的局域网主机能够通信。在生产环境中只需要利用路由器（路由器有DHCP的功能）的单臂路由的功能，在原来的基础上，添加另一个IP地址，就可以通过路由器，让不同网段的局域网主机进行通信。  
下面为模拟实验环境  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjE5MzQ4OQ_size_16_color_FFFFFF_t_70 12]  
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## 4.4 DHCP中继 ##

模拟的环境就是，局域网A网段的主机A，通过DHCP服务+一台DHCP中继器，可以将局域网B网段的主机B进行连接，使得DHCP服务可以为不同网段的主机，实现分配IP的功能，依靠的就是DHCP中继服务的能力。  
下图为本人粗略根据理解所画的草图，正确性不敢保证  
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