DHCP Client

1. dhclient 命令用於從 DHCP 服務器取得、更新和釋放客戶端 IP 地址、子網遮罩 (subnet mask) 、預設閘道 (gateway)和 DNS 服務器。
2. 安裝 dhcp-client 套件

   [root@msi ~]# dnf install dhcp-client
   

3. 查看網卡。

   [root@999999 ~]# nmcli device
   DEVICE  TYPE      STATE      CONNECTION
   ens3    ethernet  connected  ens3
   lo      loopback  unmanaged  --
   

4. 網卡 ens3 從 dhcp 伺服器取得 ip。

   [root@999999 ~]# dhclient ens3
   

5. 查看網卡 ens3 從 dhcp 伺服器取得 ip 為 192.168.122.153/24。

   [root@999999 ~]# ip addr
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
       link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
       inet 127.0.0.1/8 scope host lo
          valid_lft forever preferred_lft forever
       inet6 ::1/128 scope host
          valid_lft forever preferred_lft forever
   2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
       link/ether 52:54:00:bd:81:12 brd ff:ff:ff:ff:ff:ff
       altname enp0s3
       inet 192.168.122.153/24 brd 192.168.122.255 scope global dynamic noprefixroute ens3
          valid_lft 3651sec preferred_lft 3651sec
       inet6 2001:ac18::5054:ff:febd:8112/64 scope global dynamic noprefixroute
          valid_lft 3346sec preferred_lft 3346sec
       inet6 fe80::5054:ff:febd:8112/64 scope link noprefixroute
          valid_lft forever preferred_lft forever
   

6. 網卡 ens3 從 dhcp 伺服器取得 ip 的訊息寫在 dhclient.leases。

   [root@999999 ~]# cat /var/lib/dhclient/dhclient.leases
   lease {
     interface "ens3";
     fixed-address 192.168.122.153;
     option subnet-mask 255.255.255.0;
     option routers 192.168.122.1;
     option dhcp-lease-time 3600;
     option dhcp-message-type 5;
     option domain-name-servers 192.168.122.1;
     option dhcp-server-identifier 192.168.122.1;
     option dhcp-renewal-time 1800;
     option broadcast-address 192.168.122.255;
     option dhcp-rebinding-time 3150;
     option domain-name "deyu.wang";
     renew 1 2023/09/04 08:20:17;
     rebind 1 2023/09/04 08:47:43;
     expire 1 2023/09/04 08:55:13;
   }
   

7. 釋放網卡 ens3 取得的 ip。

   [root@999999 ~]# dhclient -r ens3
   Killed old client process
   

8. 查看網卡 ens3，已無 ip。

   [root@999999 ~]# ip addr
   1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
       link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
       inet 127.0.0.1/8 scope host lo
          valid_lft forever preferred_lft forever
       inet6 ::1/128 scope host
          valid_lft forever preferred_lft forever
   2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
       link/ether 52:54:00:bd:81:12 brd ff:ff:ff:ff:ff:ff
       altname enp0s3
       inet6 2001:ac18::5054:ff:febd:8112/64 scope global dynamic noprefixroute
          valid_lft 3191sec preferred_lft 3191sec
       inet6 fe80::5054:ff:febd:8112/64 scope link noprefixroute
          valid_lft forever preferred_lft forever