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Linux系统上DHCP服务器的配置 . [复制链接]

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发表于 2011-11-23 16:03 |只看该作者 |倒序浏览

Linux系统上DHCP服务器的配置 .

一、DHCP的工作流程

(1) DHCP服务器发现阶段。DHCP客户机向广播地址255.255.255.255发送DHCPDiscover消息。

(2) DHCP服务器响应阶段。DHCP服务器从尚未出租的IP地址池中选择一个分配给DHCP客户机，向DHCP客户机发送一个包含出租的IP地址和其他设置的DHCPoffer提供信息。

(3) IP地址选择阶段。DHCP客户机选择某个DHCP服务器提供的IP地址，以广播方式回答一个DHCPrequest请求信息.

(4) IP地址确认阶段。服务器回应包含它所提供的IP地址和其他设置的DHCPack确认信息。然后客户机将其与TCP/IP协议与网卡绑定。

(5) 客户机重新登录。再次发送前次分配的IP地址的DHCPRequest请求请求信息，DHCP服务器检查是否可以继续让客户机使用，然后发回DHCPack确认信息或者DHCPnck否认信息。如果IP已不能用，客户机需从(1)开始重新申请。

(6) 更新租约。IP地址租借期限到了，如果DHCP客户机要延长其租约，必须更新。DHCP客户机启动时和IP租约期限过一半时，都会向服务器发送更新期IP租约的信息。

二、DHCP服务器配置文件

路径在/etc/dhcp/dhcpd.conf。下面是一个配置文件的例子：

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01.<span style="font-size:16px;"># dhcpd.conf
02.#
03.# Sample configuration file for ISC dhcpd
04.#
05.
06.# option definitions common to all supported networks...
07.option domain-name "example.org";
08.option domain-name-servers ns1.example.org, ns2.example.org;
09.
10.default-lease-time 600;
11.max-lease-time 7200;
12.
13.# Use this to enble / disable dynamic dns updates globally.
14.#ddns-update-style none;
15.
16.# If this DHCP server is the official DHCP server for the local
17.# network, the authoritative directive should be uncommented.
18.#authoritative;
19.
20.# Use this to send dhcp log messages to a different log file (you also
21.# have to hack syslog.conf to complete the redirection).
22.log-facility local7;
23.
24.# No service will be given on this subnet, but declaring it helps the
25.# DHCP server to understand the network topology.
26.
27.subnet 10.152.187.0 netmask 255.255.255.0 {
28.}
29.
30.# This is a very basic subnet declaration.
31.
32.subnet 10.254.239.0 netmask 255.255.255.224 {
33. range 10.254.239.10 10.254.239.20;
34. option routers rtr-239-0-1.example.org, rtr-239-0-2.example.org;
35.}
36.
37.# This declaration allows BOOTP clients to get dynamic addresses,
38.# which we don't really recommend.
39.
40.subnet 10.254.239.32 netmask 255.255.255.224 {
41. range dynamic-bootp 10.254.239.40 10.254.239.60;
42. option broadcast-address 10.254.239.31;
43. option routers rtr-239-32-1.example.org;
44.}
45.
46.# A slightly different configuration for an internal subnet.
47.subnet 10.5.5.0 netmask 255.255.255.224 {
48. range 10.5.5.26 10.5.5.30;
49. option domain-name-servers ns1.internal.example.org;
50. option domain-name "internal.example.org";
51. option routers 10.5.5.1;
52. option broadcast-address 10.5.5.31;
53. default-lease-time 600;
54. max-lease-time 7200;
55.}
56.
57.# Hosts which require special configuration options can be listed in
58.# host statements. If no address is specified, the address will be
59.# allocated dynamically (if possible), but the host-specific information
60.# will still come from the host declaration.
61.
62.host passacaglia {
63. hardware ethernet 0:0:c0:5d:bd:95;
64. filename "vmunix.passacaglia";
65. server-name "toccata.fugue.com";
66.}
67.
68.# Fixed IP addresses can also be specified for hosts. These addresses
69.# should not also be listed as being available for dynamic assignment.
70.# Hosts for which fixed IP addresses have been specified can boot using
71.# BOOTP or DHCP. Hosts for which no fixed address is specified can only
72.# be booted with DHCP, unless there is an address range on the subnet
73.# to which a BOOTP client is connected which has the dynamic-bootp flag
74.# set.
75.host fantasia {
76. hardware ethernet 08:00:07:26:c0:a5;
77. fixed-address fantasia.fugue.com;
78.}
79.
80.# You can declare a class of clients and then do address allocation
81.# based on that. The example below shows a case where all clients
82.# in a certain class get addresses on the 10.17.224/24 subnet, and all
83.# other clients get addresses on the 10.0.29/24 subnet.
84.
85.class "foo" {
86. match if substring (option vendor-class-identifier, 0, 4) = "SUNW";
87.}
88.
89.shared-network 224-29 {
90. subnet 10.17.224.0 netmask 255.255.255.0 {
91. option routers rtr-224.example.org;
92. }
93. subnet 10.0.29.0 netmask 255.255.255.0 {
94. option routers rtr-29.example.org;
95. }
96. pool {
97. allow members of "foo";
98. range 10.17.224.10 10.17.224.250;
99. }
100. pool {
101. deny members of "foo";
102. range 10.0.29.10 10.0.29.230;
103. }
104.}
105.</span>
<span style="font-size:16px;"># 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 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;
}
}
</span>

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DHCP配置文件通常包括3部分：declarations, parameters, options。
declarations：描述网络的布局；描述客户；提供客户的地址。

parameters：表明如何执行任务，是否要执行任务，或将哪些网络配置选项发送给客户。

option：配置DHCP可选参数。

常用声明：

shared-network 告知DHCP服务器是否为一些子网络分享相同网络

subnet 描述一个IP是否属于子网

range 提供动态分配IP地址的起始和结束范围

host 为特定的主机提供网络参数

group 为一组参数提供声明

常用参数：

ddns-update-style 配置DHCP-DNS互动更新模式

default-lease-time 指定默认租赁时间的长度，单位为秒

max-lease-time 指定最大租赁时间长度，单位为秒

hardware 指定网卡接口类型和MAC地址

server-name 告知DHCP客户服务器名称

fixed-address 为客户端指定一个固定的IP地址

常用选项：

domain-name 为客户端指定域名

domain-name-servers为客户端指明DNS服务器IP地址

host-name 为客户端指明主机名称

routers 为客户端指明默认网关

broadcast-address 为客户端设定广播地址

subnet-mask 为客户端设定子网掩码

ntp-server 为客户端设定格林威治时间的偏移时间，单位为秒

下面是一个DHCPv6的配置文件的例子：

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01.# Server configuration file example for DHCPv6
02.# From the file used for TAHI tests.
03.
04.# IPv6 address valid lifetime
05.# (at the end the address is no longer usable by the client)
06.# (set to 30 days, the usual IPv6 default)
07.default-lease-time 2592000;
08.
09.# IPv6 address preferred lifetime
10.# (at the end the address is deprecated, i.e., the client should use
11.# other addresses for new connections)
12.# (set to 7 days, the usual IPv6 default)
13.preferred-lifetime 604800;
14.
15.# T1, the delay before Renew
16.# (default is 1/2 preferred lifetime)
17.# (set to 1 hour)
18.option dhcp-renewal-time 3600;
19.
20.# T2, the delay before Rebind (if Renews failed)
21.# (default is 3/4 preferred lifetime)
22.# (set to 2 hours)
23.option dhcp-rebinding-time 7200;
24.
25.# Enable RFC 5007 support (same than for DHCPv4)
26.allow leasequery;
27.
28.# Global definitions for name server address(es) and domain search list
29.option dhcp6.name-servers 3ffe:501:ffff:100:200:ff:fe00:3f3e;
30.option dhcp6.domain-search "test.example.com","example.com";
31.
32.# Set preference to 255 (maximum) in order to avoid waiting for
33.# additional servers when there is only one
34.##option dhcp6.preference 255;
35.
36.# Server side command to enable rapid-commit (2 packet exchange)
37.##option dhcp6.rapid-commit;
38.
39.# The delay before information-request refresh
40.# (minimum is 10 minutes, maximum one day, default is to not refresh)
41.# (set to 6 hours)
42.option dhcp6.info-refresh-time 21600;
43.
44.# The path of the lease file
45.dhcpv6-lease-file-name "/usr/local/var/db/dhcpd6.leases";
46.
47.# Static definition (must be global)
48.host myclient {
49. # The entry is looked up by this
50. host-identifier option
51. dhcp6.client-id 00:01:00:01:00:04:93:e0:00:00:00:00:a2:a2;
52.
53. # A fixed address
54. fixed-address6 3ffe:501:ffff:100::1234;
55.
56. # A fixed prefix
57. fixed-prefix6 3ffe:501:ffff:101::/64;
58.
59. # Override of the global definitions,
60. # works only when a resource (address or prefix) is assigned
61. option dhcp6.name-servers 3ffe:501:ffff:100:200:ff:fe00:4f4e;
62.
63. # For debug (to see when the entry statements are executed)
64. # (log "sol" when a matching Solicitation is received)
65. ##if packet(0,1) = 1 { log(debug,"sol"); }
66.}
67.
68.# The subnet where the server is attached
69.# (i.e., the server has an address in this subnet)
70.subnet6 3ffe:501:ffff:100::/64 {
71. # Two addresses available to clients
72. # (the third client should get NoAddrsAvail)
73. range6 3ffe:501:ffff:100::10 3ffe:501:ffff:100::11;
74.
75. # Use the whole /64 prefix for temporary addresses
76. # (i.e., direct application of RFC 4941)
77. range6 3ffe:501:ffff:100:: temporary;
78.
79. # Some /64 prefixes available for Prefix Delegation (RFC 3633)
80. prefix6 3ffe:501:ffff:100:: 3ffe:501:ffff:111:: /64;
81.}
82.
83.# A second subnet behind a relay agent
84.subnet6 3ffe:501:ffff:101::/64 {
85. range6 3ffe:501:ffff:101::10 3ffe:501:ffff:101::11;
86.
87. # Override of the global definitions,
88. # works only when a resource (address or prefix) is assigned
89. option dhcp6.name-servers 3ffe:501:ffff:101:200:ff:fe00:3f3e;
90.
91.}
92.
93.# A third subnet behind a relay agent chain
94.subnet6 3ffe:501:ffff:102::/64 {
95. range6 3ffe:501:ffff:102::10 3ffe:501:ffff:102::11;
96.}

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