gtalent深度讲解DHCP服务

575 05-10

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DHCP实现
注意：实现DHCP服务前，先将网络已有DHCP服务，如：vmware中的DHCP关闭，访止冲突

DHCP服务的实现软件：

dhcp（CentOS 7 之前版本）或 dhcp-server（CentOS 8 中的包名）
dnsmasq：小型服务软件，可以提供dhcp和dns功能
1 DHCP相关文件组成
dhcp或dhcp-server 包文件组成
/usr/sbin/dhcpd dhcp服务主程序
/etc/dhcp/dhcpd.conf dhcp服务配置文件
/usr/share/doc/dhcp-server/dhcpd.conf.example #dhcp服务配置范例文件
/usr/lib/systemd/system/dhcpd.service #dhcp服务service文件
/var/lib/dhcpd/dhcpd.leases 地址分配记录
dhcp-client客户端包
/usr/sbin/dhclient #客户端程序
/var/lib/dhclient #自动获取的IP信息
windows 工具
ipconfig /release #释放DHCP获取的IP，重新申请IP
ipconfig/renew #刷新租约，续约

2 DHCP服务器配置文件
注意：

DHCP服务器本身采用静态IP
必须配置和DHCP网卡的静态IP所在网段的subent段，否则DHCP服务无法启动
/etc/dhcp/dhcpd.conf格式

全局配置
subnet {
...
}
host {
}

3 DHCP实现

#centos实现DHCP
[root@centos7 ~]# yum install dhcp
[root@centos7 ~]# cp /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example /etc/dhcp/dhcpd.conf					#修改DHCP配置文件
[root@centos7 ~]# vim /etc/dhcp/dhcpd.conf 
 8 # 设置dns
 9 option domain-name-servers 180.76.76.76,223.5.5.5;
 10 # 租期以秒为单位
 11 default-lease-time 86400;
 12 # 最大有效期，一般用不到
 13 max-lease-time 100000;
 28 # 设置地址池和网关
 29 subnet 10.0.0.0 netmask 255.255.255.0 {
 30   range 10.0.0.40 10.0.0.80;
 31   option routers 10.0.0.2;
 32 }
 [root@centos7 ~]# systemctl enable --now dhcpd
[root@centos7 ~]# systemctl status dhcpd
● dhcpd.service - DHCPv4 Server Daemon
   Loaded: loaded (/usr/lib/systemd/system/dhcpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Sat 2021-05-08 15:12:52 CST; 4min 51s ago
     Docs: man:dhcpd(8)
           man:dhcpd.conf(5)
 Main PID: 2713 (dhcpd)
   Status: "Dispatching packets..."
   CGroup: /system.slice/dhcpd.service
           └─2713 /usr/sbin/dhcpd -f -cf /etc/dhcp/dhcpd.conf -user dhcpd -group dhcpd --no-pid

May 08 15:12:52 centos7 dhcpd[2713]: All rights reserved.
May 08 15:12:52 centos7 dhcpd[2713]: For info, please visit https://www.isc.org/software/dhcp/
May 08 15:12:52 centos7 dhcpd[2713]: Wrote 0 class decls to leases file.
May 08 15:12:52 centos7 dhcpd[2713]: Wrote 0 deleted host decls to leases file.
May 08 15:12:52 centos7 dhcpd[2713]: Wrote 0 new dynamic host decls to leases file.
May 08 15:12:52 centos7 dhcpd[2713]: Wrote 0 leases to leases file.
May 08 15:12:52 centos7 dhcpd[2713]: Listening on LPF/eth0/00:0c:29:e6:d5:03/10.0.0.0/24
May 08 15:12:52 centos7 dhcpd[2713]: Sending on   LPF/eth0/00:0c:29:e6:d5:03/10.0.0.0/24
May 08 15:12:52 centos7 dhcpd[2713]: Sending on   Socket/fallback/fallback-net
May 08 15:12:52 centos7 systemd[1]: Started DHCPv4 Server Daemon.

3.1 查看地址池中分配出去已经使用的地址

[root@centos7 ~]# cat /var/lib/dhcpd/dhcpd.leases
# The format of this file is documented in the dhcpd.leases(5) manual page.
# This lease file was written by isc-dhcp-4.2.5

server-duid "\000\001\000\001((\366t\000\014)\346\325\003";

lease 10.0.0.40 {
  starts 6 2021/05/08 07:18:33;				#获取IP地址时间，时区为UTC
  ends 0 2021/05/09 07:18:33;				#IP地址过期时间，时区为UTC
  cltt 6 2021/05/08 07:18:33;
  binding state active;
  next binding state free;
  rewind binding state free;
  hardware ethernet 00:0c:29:3b:41:64;		#使用此IP地址的机器的mac地址
}

3.2 已有静态地址，再次获取一个动态地址

[root@centos7 ~]# ip a
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: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:0c:29:c5:bd:97 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.207/24 brd 10.0.0.255 scope global noprefixroute eth0
       valid_lft forever preferred_lft forever
[root@centos7 ~]# dhclient -d
Internet Systems Consortium DHCP Client 4.2.5
Copyright 2004-2013 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/00:0c:29:c5:bd:97
Sending on   LPF/eth0/00:0c:29:c5:bd:97
Sending on   Socket/fallback
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 3 (xid=0x76331da)
DHCPREQUEST on eth0 to 255.255.255.255 port 67 (xid=0x76331da)
DHCPOFFER from 10.0.0.217
DHCPACK from 10.0.0.217 (xid=0x76331da)
bound to 10.0.0.41 -- renewal in 38316 seconds.			#获取到的IP地址

3.3 通过mac地址进行IP地址绑定

在服务器端进行修改配置文件

[root@centos7 ~]# vim /etc/dhcp/dhcpd.conf
 65 host testhost{
 66     hardware ethernet 00:0c:29:3b:41:64;
 67     fixed-address 10.0.0.40;                                                
 68 }
[root@centos7 ~]# systemctl restart dhcpd			#重启服务

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