DHCP通訊模式

通訊的4個(gè)步驟

(1) Client：dhcp discover
(2) Server: dhcp offer(IP/Netmask, GW, DNS Server, NTP Server, Wins Server, ...)
(3) Client：dhcp request
(4) Server：dhcp ack

相關(guān)名詞

lease time: 租約期限
arp: IP ---> Mac
rarp: Mac ---> IP

DHCP動(dòng)態(tài)主機(jī)管理協(xié)議(Dynamic Host Configuration Protocol)是一種基于UDP協(xié)議且僅限用于局域網(wǎng)的網(wǎng)絡(luò)協(xié)議，主要用途是為局域網(wǎng)內(nèi)部設(shè)備或網(wǎng)絡(luò)供應(yīng)商自動(dòng)分配IP地址，通常會應(yīng)用在大型的局域網(wǎng)環(huán)境中或局域網(wǎng)內(nèi)存在比較多的移動(dòng)辦公設(shè)備，DHCP協(xié)議能夠?qū)崿F(xiàn)集中的管理、分配IP地址。
DHCP服務(wù)程序能夠使局域網(wǎng)內(nèi)的主機(jī)自動(dòng)且動(dòng)態(tài)的獲取IP地址、子網(wǎng)掩碼、網(wǎng)關(guān)地址以及DNS服務(wù)器地址等信息，且能夠有效的提升地址使用率，提高配置效率，減少管理和維護(hù)成本。
DHCP協(xié)議能夠保證任何IP地址在同一時(shí)刻只能由一臺DHCP客戶機(jī)使用，且能夠?yàn)橹付ㄖ鳈C(jī)分配固定的IP地址。

DHCP服務(wù)器的配置

• 實(shí)現(xiàn)
  dhcp (isc.org) - The dhcp package provides the ISC DHCP service and relay agent.
  dnsmasq (dns, dhcp) - Dnsmasq is lightweight, easy to configure DNS forwarder and DHCP server. It is designed to provide DNS and, optionally, DHCP, to a small network.

• 安裝:
  yum -y install dhcp

• 程序環(huán)境
  dhcp server：
  程序文件: /usr/sbin/dhcpd
  IPV4網(wǎng)絡(luò)：
  配置文件: /etc/dhcp/dhcpd.conf # 默認(rèn)為空,可從/usr/share/doc/dhcp/-xxx/dhcpd.conf.example拷貝
  UnitFile: /usr/lib/systemd/system/dhcpd.service
  IPV6網(wǎng)絡(luò)：
  /etc/dhcp/dhcpd6.conf
/usr/lib/systemd/system/dhcpd6.service
  dhcprelay：中繼,必須先對本地局域網(wǎng)中的主機(jī)提供服務(wù)
  /usr/sbin/dhcrelay
/usr/lib/systemd/system/dhcrelay.service

• 配置文件說明
  配置指令
  options --> 配置給客戶端的相關(guān)信息
  指令 ---> 定義dhcp server的工作特性

# dhcpd.conf
# Sample configuration file for ISC dhcpd
# option definitions common to all supported networks...
option domain-name "example.org";    # 搜索的頂級域
option domain-name-servers ns1.example.org, ns2.example.org;  # 指定的DNS域名服務(wù)器
default-lease-time 600;       # 默認(rèn)的租期時(shí)長
max-lease-time 7200;          # 最大的租期
# 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;
    }
}