DHCP概述
1）了解DHCP服务
DHCP（Dynimic Host Configuration Protocol，动态主机配置协议）是由IEIF（Internet工作任务小组）设计开发的，专门用于为TCP/IP网络的计算机自动分配TCP/IP参数的协议，DHCP服务避免了因手工设置IP地址所产生的错误，同时也避免了把一个IP地址分配给多台工作站所造成的地址冲突；DHCP提供了安全，可靠且简单的TCP/IP网络设置，降低了配置IP地址的负担
2）使用DHCP的好处
减少管理员的工作量
避免输入错误的可能
避免IP冲突
当网更改IP地址段时，不需要在重新配置每个用户的IP地址
提高了IP地址的利用率
方便客户端的配置
DHCP的工作原理
1）DHCP的分配方式
DHCP服务器提供了三种IP分配方式：自动分配、手动分配和动态分配
自动分配是当DHCP客户机第一次成功的从DHCP服务器获取到一个IP地址后，就永久地使用这个IP地址
手动分配是由DHCP服务器管理员专门指定IP地址
动态分配时当DHCP客户机第一次从DHCP服务器获取到IP地址后，并非永久地使用该地址，每次使用完后，DHCP客户机就需要释放这个IP地址，供其他客户机使用
2）DHCP的租约过程
客户机从DHCP服务器获得IP地址的过程称为DHCP的租约过程；租约过程分为四个步骤：
客户机请求IP地址（客户机发DHCP Discover广播包）
服务器响应（服务器发DHCP Offer广播包）
客户机选择IP地址（客户机发DHCP Request广播包）
服务器确定租约（服务器发DHCP ACK广播包）
1、客户端请求IP
DHCP Discover
2、服务器响应
DHCP Offer
3、客户机选择IP
DHCP Request
4、服务器确定租约
DHCP ACK
5、重新接入网络
dhcp软件安装
dhcp软件在系统镜像光盘里就已经提供了，只需要使用rpm或者yum软件安装即可
如果使用yum安装需要提前配置好yum
[[email protected] ~]# mkdir /mnt/cdrom [[email protected] ~]# mount /dev/cdrom /mnt/cdr [[email protected] ~]# cat /etc/yum.repos.d/base.repo [base] name=centos baseurl=file:///mnt/cdrom enabled=1 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-$releasever [[email protected] ~]# rpm -ivh /mnt/cdrom/Packages/dhcp-4.2.5-42.el7.centos.x86_64.rpm 或者 [[email protected] ~]# yum install -y dhcp 使用下面的命令可以查看dhcp软件的介绍和安装生成文件及目录 [[email protected] ~]# yum info dhcp Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile Installed Packages Name : dhcp Arch : x86_64 Epoch : 12 Version : 4.2.5 Release : 42.el7.centos Size : 1.4 M Repo : installed Summary : Dynamic host configuration protocol software URL : http://isc.org/products/DHCP/ License : ISC Description : DHCP (Dynamic Host Configuration Protocol) is a protocol which allows : individual devices on an IP network to get their own network : configuration information (IP address, subnetmask, broadcast address, : etc.) from a DHCP server. The overall purpose of DHCP is to make it : easier to administer a large network. : : To use DHCP on your network, install a DHCP service (or relay agent), : and on clients run a DHCP client daemon. The dhcp package provides : the ISC DHCP service and relay agent. [[email protected] ~]# rpm -ql dhcp /etc/NetworkManager /etc/NetworkManager/dispatcher.d /etc/NetworkManager/dispatcher.d/12-dhcpd /etc/dhcp /etc/dhcp/dhcpd.conf /etc/dhcp/dhcpd6.conf /etc/openldap/schema/dhcp.schema /etc/sysconfig/dhcpd /usr/bin/omshell /usr/lib/systemd/system/dhcpd.service /usr/lib/systemd/system/dhcpd6.service /usr/lib/systemd/system/dhcrelay.service /usr/sbin/dhcpd /usr/sbin/dhcrelay /usr/share/doc/dhcp-4.2.5 /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example /usr/share/doc/dhcp-4.2.5/dhcpd6.conf.example /usr/share/doc/dhcp-4.2.5/ldap /usr/share/doc/dhcp-4.2.5/ldap/README.ldap /usr/share/doc/dhcp-4.2.5/ldap/dhcp.schema /usr/share/doc/dhcp-4.2.5/ldap/dhcpd-conf-to-ldap /usr/share/man/man1/omshell.1.gz /usr/share/man/man5/dhcpd.conf.5.gz /usr/share/man/man5/dhcpd.leases.5.gz /usr/share/man/man8/dhcpd.8.gz /usr/share/man/man8/dhcrelay.8.gz /usr/share/systemtap/tapset/dhcpd.stp /var/lib/dhcpd /var/lib/dhcpd/dhcpd.leases /var/lib/dhcpd/dhcpd6.leases
dhcp基本配置
前提条件：
DHCP服务器与客户端主机已正常连通，并在同一网络中
如果客户端主机使用了DHCP方式动态获取IP地址，而网络中没有DHCP服务器，或者服务器出现问题，则客户端就不能正常取得地址了；如果是Windows，它将从B类网段192.254.0.0中挑选一个IP地址作为自己的IP地址，并继续每隔5分钟尝试与DHCP服务器进行通信，一旦与DHCP取得通信，客户机将放弃自己配置的IP地址，使用DHCP服务器分配的IP地址；
1、DHCP服务器配置
DHCP服务器需要向客户端分配IP地址，服务器自身需要使用一个静态的IP地址
[[email protected] ~]# ifconfig eno16777736
eno16777736: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.16.1.10 netmask 255.255.0.0 broadcast 172.16.255.255
inet6 fe80::20c:29ff:fe65:8475 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:65:84:75 txqueuelen 1000 (Ethernet)
RX packets 7051 bytes 6763047 (6.4 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 1808 bytes 225665 (220.3 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
[[email protected] ~]# vi /etc/dhcp/dhcpd.conf
...
option domain-name "bsg.com";
option domain-name-servers 202.106.0.20, 8.8.8.8，172.16.1.254;
default-lease-time 3600;
max-lease-time 7200;
...
subnet 172.16.1.0 netmask 255.255.0.0 {
range 172.16.1.100 172.16.1.200
}
...
[[email protected] ~]# systemctl start dhcpd.service
[[email protected] ~]# ss -tunl
Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port
udp UNCONN 0 0 *:40620 *:*
udp UNCONN 0 0 *:67 *:*
udp UNCONN 0 0 :::18696 :::*
tcp LISTEN 0 128 *:22 *:*
tcp LISTEN 0 100 127.0.0.1:25 *:*
tcp LISTEN 0 128 :::22 :::*
tcp LISTEN 0 100 ::1:25 :::*
2、客户端主机配置
如果客户端之前使用静态的IP地址，需要将获取方式改为dhcp自动获取并删除IP地址，修改完配置文件后重新启动网卡
Linux客户端
Windows客户端
在DHCP服务器上查看IP地址分配及租约情况
[[email protected] ~]# 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
lease 172.16.1.102 {
starts 2 2016/11/01 13:55:33;
ends 2 2016/11/01 13:57:51;
tstp 2 2016/11/01 13:57:51;
cltt 2 2016/11/01 13:55:33;
binding state free;
hardware ethernet 00:0c:29:96:ea:a9;
uid "\001\000\014)\226\352\251";
}
lease 172.16.1.100 {
starts 2 2016/11/01 13:56:35;
ends 2 2016/11/01 14:06:35;
tstp 2 2016/11/01 14:06:35;
cltt 2 2016/11/01 13:56:35;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:0c:29:9d:3a:2a;
}
server-duid "\000\001\000\001\037\253K\017\000\014)e\204u";
为客户机保留IP地址
1、获取客户机的mac地址
2、修改DHCP的配置文件
mac地址不区分大小写，windows客户端的mac地址中的"-"需要换成":"
[[email protected] ~]# vi /etc/dhcp/dhcpd.conf
...
host ftpsrv {
hardware ethernet 00:0c:29:9d:3a:2a;
fixed-address 172.16.1.253;
}
host winc1 {
hardware ethernet 00:0c:29:96:ea:a9;
fixed-address 172.16.1.50;
}
...
[[email protected] ~]# systemctl restart dhcpd.service
[[email protected] ~]# ss -tnul
Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port
udp UNCONN 0 0 *:67 *:*
udp UNCONN 0 0 *:31306 *:*
udp UNCONN 0 0 :::45651 :::*
tcp LISTEN 0 128 *:22 *:*
tcp LISTEN 0 100 127.0.0.1:25 *:*
tcp LISTEN 0 128 :::22 :::*
tcp LISTEN 0 100 ::1:25 :::*
3、客户端重新获取IP地址
