介绍
vmware虚拟机的仅主机模式中，一般都会选择dhcp服务,给vmware中仅主机模式的linux网络适配器分配ip地址，如图1。现在，关闭图1中的仅主机模式的dhcp服务，在虚拟机中centos7上面搭建一个dhcp服务，以便为虚拟机中的其它主机提供dhcp服务。
另外，此处搭建的dhcp实验，是为下一个实验(从网络自动化安装centos操作系统做准备)
如图1，停止仅主机模式的dhcp服务，则vmware上的虚拟主机靠dhcp获取ip失败，只能手动配置ip，以便dhcp服务只有本地centos7即将搭建的dhcp服务
小插曲
ifconfig命令出现的名为virbr0的虚拟网卡：
在centos7里安装 Xen 或安装 KVM 后，会发现网络接口里多了一个叫做 virbr0 的虚拟网络接口，并且会自动获得一个私有地址(virbr0网卡的IP地址都为192.168.122.1)，
这是在安装和启用了libvirt 服务后生成的，libvirt 在服务器host上生成一个 virtual network switch (virbr0)，host上所有的虚拟机（guests）通过这个 virbr0 连起来。
默认情况下 virbr0 使用的是 NAT 模式（采用 IP Masquerade），所以这种情况下 guest 通过 host 才能访问外部。
大多数时候我们使用虚拟机 bridge(桥接)直接连到局域网里，所以这个 virbr0 不是必须的（注：bridge 和这里的 virbr0 bridge 是互不相干的）。
关掉这个 virbr0 的步骤如下
virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:3d:9a:f8 txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0[root@centos7:~]# yum search virsh
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
====================================== N/S matched: virsh ======================================
fence-agents-virsh.x86_64 : Fence agent for virtual machines based on libvirt
Name and summary matches only, use "search all" for everything.
[root@centos7:~]# yum install fence-agents-virsh.x86_64
[root@centos7:~]# virsh net-destroy default
Network default destroyed
[root@centos7:~]# virsh net-undefine default
Network default has been undefined
[root@centos7:~]# systemctl restart libvirtd别人博客解决方法，尚未验证
https://blog.csdn.net/radkitty/article/details/6034577
此处删除了virbr0，且所有的虚拟机上的centos均只有一个网卡且为仅主机模式，以便简化后面的搭建centos7 dhcp服务的实验
DHCP服务
[root@centos6 dhclient ]#cd /var/lib/dhclient/ [root@centos6 dhclient ]# ls dhclient-eth0.leases [root@centos6 dhclient ]#dhclient [root@centos7:~]# yum info dhcp [root@centos7:~]# rpm -ql dhcp /etc/NetworkManager /etc/NetworkManager/dispatcher.d /etc/NetworkManager/dispatcher.d/12-dhcpd /etc/dhcp/dhcpd.conf #dhcp服务配置文件 /etc/dhcp/dhcpd6.conf /etc/dhcp/scripts /usr/lib/systemd/system/dhcpd.service /usr/lib/systemd/system/dhcpd6.service /etc/dhcp/scripts/README.scripts /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example #范例文件 /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 #分配地址记录数据库 /var/lib/dhcpd/dhcpd6.leases[root@centos7:~]# rpm -q --scripts dhcp preinstall scriptlet (using /bin/sh): # /usr/share/doc/setup/uidgid getent group dhcpd >/dev/null || groupadd --force --gid 177 --system dhcpd if ! getent passwd dhcpd >/dev/null ; then if ! getent passwd 177 >/dev/null ; then useradd --system --uid 177 --gid dhcpd --home / --shell /sbin/nologin --comment "DHCP server" dhcpd else useradd --system --gid dhcpd --home / --shell /sbin/nologin --comment "DHCP server" dhcpd fi [root@centos7:~]# cat /etc/dhcp/dhcpd.conf # # DHCP Server Configuration file. # see /usr/share/doc/dhcp*/dhcpd.conf.example # see dhcpd.conf(5) man page # [root@centos7:~]#
启动dhcpd服务
[root@centos7:~]# systemctl start dhcpd Job for dhcpd.service failed because the control process exited with error code. See "systemctl status dhcpd.service" and "journalctl -xe" for details. [root@centos7:~]# systemctl status dhcpd ● dhcpd.service - DHCPv4 Server Daemon Loaded: loaded (/usr/lib/systemd/system/dhcpd.service; disabled; vendor preset: disabled) Active: failed (Result: exit-code) since Sun 2018-07-15 21:04:01 CST; 8s ago Docs: man:dhcpd(8) man:dhcpd.conf(5) Process: 12903 ExecStart=/usr/sbin/dhcpd -f -cf /etc/dhcp/dhcpd.conf -user dhcpd -group dhcpd --no-pid (code=exited, status=1/FAILURE) Main PID: 12903 (code=exited, status=1/FAILURE) Jul 15 21:04:01 centos7 dhcpd[12903]: For info, please visit https://www.isc.org/software/dhcp/ Jul 15 21:04:01 centos7 dhcpd[12903]: Not searching LDAP since ldap-server, ldap-port and ...ile Jul 15 21:04:01 centos7 dhcpd[12903]: Wrote 0 leases to leases file. Jul 15 21:04:01 centos7 dhcpd[12903]: Jul 15 21:04:01 centos7 dhcpd[12903]: No subnet declaration for ens38 (192.168.139.128). Jul 15 21:04:01 centos7 dhcpd[12903]: ** Ignoring requests on ens38. If this is not what Jul 15 21:04:01 centos7 systemd[1]: dhcpd.service: main process exited, code=exited, statu...URE Jul 15 21:04:01 centos7 systemd[1]: Failed to start DHCPv4 Server Daemon. Jul 15 21:04:01 centos7 systemd[1]: Unit dhcpd.service entered failed state. Jul 15 21:04:01 centos7 systemd[1]: dhcpd.service failed. Hint: Some lines were ellipsized, use -l to show in full. [root@centos7:~]#报错原因：由于dhcp服务是就近为本网段服务的，如果不定义本网络的dhcp服务主机ip所在的子网ip范围，会报错。只有配置好为本网络中的主机提供dhcp服务的ip范围，再向外网主机提供dhcp，才不会报错
根据上述的dhcpd的配置文件的描述， [root@centos7:~]# cp /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example /etc/dhcp/dhcpd.conf [root@centos7:~]# cat /etc/dhcp/dhcpd.conf # dhcpd.conf # # Sample configuration file for ISC dhcpd # # option definitions common to all supported networks... #option domain-name "example.org"; #此处的同/etc/resolv.conf,示例如下 option domain-name "baidu.com"; #option domain-name-servers ns1.example.org, ns2.example.org; dns解析示例，此行修改 option domain-name-servers 114.114.114.114,1.1.1.1; default-lease-time 600; #dhcp的ip地址租期 max-lease-time 7200; #最大租期(单位：秒) # 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 { #} subnet 192.168.31.0 netmask 255.255.255.0 { range 192.168.31.100 192.168.31.130; #配置一个本网段的dhcp服务ip范围 option routers 192.168.31.254; #可以添加网关 } # 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 10.5.5.0 netmask 255.255.255.224 { range 10.5.5.26 10.5.5.30; 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; } # Hosts which require special configuration options can be listed in # host statements. If no address is specified, the address will be # allocated dynamically (if possible), but the host-specific information # will still come from the host declaration. host passacaglia { hardware ethernet 0:0:c0:5d:bd:95; filename "vmunix.passacaglia"; server-name "toccata.fugue.com"; } # Fixed IP addresses can also be specified for hosts. These addresses # should not also be listed as being available for dynamic assignment. # Hosts for which fixed IP addresses have been specified can boot using # BOOTP or DHCP. Hosts for which no fixed address is specified can only # be booted with DHCP, unless there is an address range on the subnet # to which a BOOTP client is connected which has the dynamic-bootp flag # set. host fantasia { hardware ethernet 08:00:07:26:c0:a5; fixed-address fantasia.fugue.com; } # You can declare a class of clients and then do address allocation # based on that. The example below shows a case where all clients # in a certain class get addresses on the 10.17.224/24 subnet, and all # other clients get addresses on the 10.0.29/24 subnet. class "foo" { match if substring (option vendor-class-identifier, 0, 4) = "SUNW"; } shared-network 224-29 { subnet 10.17.224.0 netmask 255.255.255.0 { option routers rtr-224.example.org; } subnet 10.0.29.0 netmask 255.255.255.0 { option routers rtr-29.example.org; } pool { allow members of "foo"; range 10.17.224.10 10.17.224.250; } pool { deny members of "foo"; range 10.0.29.10 10.0.29.230; } }
在centos7中ping www也可以，centos7中会参考如下文件中的search localdomain 自动补全
[root@centos7:~]# cat /etc/resolv.conf
# Generated by NetworkManager
search localdomain
nameserver 192.168.139.2
[root@centos7:~]#
此处给centos7一个桥接网址，以便可以访问外网
[root@centos7:~]# vim /etc/resolv.conf
[root@centos7:~]# cat /etc/resolv.conf
# Generated by NetworkManager
search baidu.com
nameserver 192.168.139.2
[root@centos7:~]#
[root@centos7:~]# ping www
PING www.a.shifen.com (61.135.169.121) 56(84) bytes of data.
64 bytes from 61.135.169.121 (61.135.169.121): icmp_seq=1 ttl=128 time=35.3 ms
64 bytes from 61.135.169.121 (61.135.169.121): icmp_seq=2 ttl=128 time=61.2 ms
^C
[root@centos7:~]# ping www.baidu.com
PING www.a.shifen.com (61.135.169.125) 56(84) bytes of data.
64 bytes from 61.135.169.125 (61.135.169.125): icmp_seq=1 ttl=128 time=72.4 ms
64 bytes from 61.135.169.125 (61.135.169.125): icmp_seq=2 ttl=128 time=119 ms
^C重启服务，不会再报错
[root@centos7:~]# systemctl start dhcpd
[root@centos7:~]# systemctl status dhcpd
● dhcpd.service - DHCPv4 Server Daemon
Loaded: loaded (/usr/lib/systemd/system/dhcpd.service; disabled; vendor preset: disabled)
Active: active (running) since Sun 2018-07-15 21:40:15 CST; 41s ago
Docs: man:dhcpd(8)开启虚拟机中的centos6，并且只有一个仅主机模式的网络适配器，获取ip如下
[root@centos6 ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:E2:9A:30
inet addr:192.168.31.100 Bcast:192.168.31.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fee2:9a30/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:68 errors:0 dropped:0 overruns:0 frame:0
TX packets:53 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:8657 (8.4 KiB) TX bytes:7605 (7.4 KiB)
[root@centos6 ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.31.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0
0.0.0.0 192.168.31.254 0.0.0.0 UG 0 0 0 eth0
[root@centos7:/var/lib/dhcpd ]# ls
dhcpd6.leases dhcpd.leases dhcpd.leases~
[root@centos7:/var/lib/dhcpd ]# less 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\"\336\353W\000\014)\020\276\272";
lease 192.168.31.100 {
starts 1 2018/07/16 05:38:10;
ends 1 2018/07/16 05:48:10;
cltt 1 2018/07/16 05:38:10;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:0c:29:e2:9a:30;
client-hostname "centos6";
}
lease 192.168.31.101 {
starts 1 2018/07/16 05:40:42;
ends 1 2018/07/16 05:50:42;
cltt 1 2018/07/16 05:40:42;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:0c:29:c2:3e:12;
client-hostname "centos7-2";
}
(END)centos6再添加一个仅主机模式的网络适配器，
[root@centos6 ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:E2:9A:30
inet addr:192.168.31.100 Bcast:192.168.31.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fee2:9a30/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:266 errors:0 dropped:0 overruns:0 frame:0
TX packets:285 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:25296 (24.7 KiB) TX bytes:28521 (27.8 KiB)
eth1 Link encap:Ethernet HWaddr 00:0C:29:E2:9A:3A
inet6 addr: fe80::20c:29ff:fee2:9a3a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:4 errors:0 dropped:0 overruns:0 frame:0
TX packets:3 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:240 (240.0 b) TX bytes:258 (258.0 b)
若要eth1的mac地址绑定一个固定的ip地址，可以在dhcp服务器上的配置文件中，绑定ip[root@centos7:~]# cat /etc/dhcp/dhcpd.conf
# set.
host fantasia {
hardware ethernet 08:00:07:26:c0:a5;
fixed-address fantasia.fugue.com;
}
找到此行，在其下面添加如下内容
host testcentos6 {
hardware ethernet 00:0C:29:E2:9A:3A;
fixed-address 192.168.31.222;
}
重启centos7中的dhcp服务
[root@centos7:/var/lib/dhcpd ]# systemctl restart dhcpd
重启一下centos6的网络服务
[root@centos6 ~]# service network restart
Shutting down interface eth0: Device state: 3 (disconnected)
[ OK ]
Shutting down loopback interface: [ OK ]
Bringing up loopback interface: [ OK ]
Bringing up interface eth0: Active connection state: activating
Active connection path: /org/freedesktop/NetworkManager/ActiveConnection/2
state: activated
Connection activated
此处eth1并没有获取到ip地址，忘记添加eth1的配置文件
[root@centos6 network-scripts]# ls
ifcfg-eth0 #没有eht1的网卡配置文件
[root@centos6 network-scripts]# cp ifcfg-eth0 ifcfg-eth1
[root@centos6 network-scripts]# ls
ifcfg-eth0 ifdown-ib ifdown-routes ifup-eth ifup-plusb ifup-wireless
ifcfg-eth1
[root@centos6 network-scripts]# vim ifcfg-eth1
DEVICE=eth0
TYPE=Ethernet
NM_CONTROLLED=yes
BOOTPROTO=dhcp
上述添加完成后，
[root@centos6 ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:E2:9A:30
inet addr:192.168.31.100 Bcast:192.168.31.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fee2:9a30/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:680 errors:0 dropped:0 overruns:0 frame:0
TX packets:761 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:62811 (61.3 KiB) TX bytes:81395 (79.4 KiB)
eth1 Link encap:Ethernet HWaddr 00:0C:29:E2:9A:3A
inet addr:192.168.31.222 Bcast:192.168.31.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fee2:9a3a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:284 errors:0 dropped:0 overruns:0 frame:0
TX packets:35 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:19967 (19.4 KiB) TX bytes:4214 (4.1 KiB)
[root@centos6 ~]# cd /var/lib/dhclient/
[root@centos6 dhclient]# ls
dhclient-5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03-eth0.lease dhclient-eth0.leases
dhclient-9c92fad9-6ecb-3e6c-eb4d-8a47c6f50c04-eth1.lease
[root@centos6 dhclient]# cat dhclient-9c92fad9-6ecb-3e6c-eb4d-8a47c6f50c04-eth1.lease
lease {
interface "eth1";
fixed-address 192.168.31.222;
option subnet-mask 255.255.255.0;
option routers 192.168.31.254;
option dhcp-lease-time 600;
option dhcp-message-type 5;
option domain-name-servers 114.114.114.114,1.1.1.1;
option dhcp-server-identifier 192.168.31.7;
option domain-name "baidu.com";
renew 1 2018/07/16 14:11:02;
rebind 1 2018/07/16 14:14:50;
expire 1 2018/07/16 14:16:05;
}
lease {
interface "eth1";
fixed-address 192.168.31.222;
option subnet-mask 255.255.255.0;
option routers 192.168.31.254;
option dhcp-lease-time 600;
option dhcp-message-type 5;
option domain-name-servers 114.114.114.114,1.1.1.1;
option dhcp-server-identifier 192.168.31.7;
option domain-name "baidu.com";
renew 1 2018/07/16 14:15:54;
rebind 1 2018/07/16 14:19:47;
expire 1 2018/07/16 14:21:02;
}
[root@centos6 dhclient]#
pxe与dhcp服务
一台主机的网卡从dhcp服务器获取ip地址后，还可以获取下一个tftp服务器的一个文件，而这个文件可以用来实现从网络引导系统自动化安装
[root@centos7:~]# cat /etc/dhcp/dhcpd.conf
# will still come from the host declaration.
host passacaglia {
hardware ethernet 0:0:c0:5d:bd:95;
filename “vmunix.passacaglia”;
next-server tftp #添加此行，下一个服务器就是可以提供此文件的tftp服务器
server-name “toccata.fugue.com”;
}
tftp轻量级服务器，文件小。而如果要引导这台主机实现从网络自动安装系统，那么这台主机的硬件网卡只能从dhcp获取一个ip地址，而没有操作系统，没有软件tftp客户端软件，如何下载文件呢？
解决方法是：一般我们现在购买电脑主机的网卡里面都集成有tpft轻量级客户端软件，只要网卡获取ip地址，网卡里的tftp客户端软件就可以下载文件了
以前的网卡集成有tftp轻量级的网卡比较贵，现在已经普及了
Preboot Excution Environment 预启动执行环境 PXE(网络自动化安装操作系统)