拓扑图

接口地址池

PC5通过接口地址池获取地址，DHCP服务器和VLAN40的网关为SW4 10.0.40.254

SW4

#
sysname Huawei
#
vlan batch 10 20 30 40
#
dhcp enable
#
interface Vlanif40ip address 10.0.40.254 255.255.255.128dhcp select interface
#
interface GigabitEthernet0/0/2port link-type trunkport trunk allow-pass vlan 10 20 40
#

SW3

#
sysname SW3
#
undo info-center enable
#
vlan batch 10 20 30 40
#
dhcp enable
#
interface Ethernet0/0/1port link-type trunkport trunk allow-pass vlan 10 20 40#
interface Ethernet0/0/4port link-type accessport default vlan 40

抓包

全局地址池&&DHCP中继

PC4和PC6通过全局地址池获取地址，

SW4

#
interface Vlanif10ip address 10.0.10.254 255.255.255.0dhcp select relaydhcp relay server-ip 10.0.30.2
#
interface Vlanif20ip address 10.0.20.254 255.255.255.0dhcp select relaydhcp relay server-ip 10.0.30.2
#
interface Vlanif30ip address 10.0.30.4 255.255.255.0
#
interface GigabitEthernet0/0/1port link-type accessport default vlan 30

SW3

#
interface Ethernet0/0/2port link-type accessport default vlan 10
#
interface Ethernet0/0/3port link-type accessport default vlan 20

 R1

跨网段一定要配置静态路由 ，服务器的回复包才能达到客户端

客户端跨网段通信是由中继实现的

#
interface GigabitEthernet0/0/0ip address 10.0.30.2 255.255.255.0 dhcp select global
#
ip route-static 10.0.10.0 255.255.255.0 10.0.30.4
ip route-static 10.0.20.0 255.255.255.0 10.0.30.4

抓包

验证

基于接口地址池获取的地址 ，客户端地址是网关同网段的IP地址

 基于全局地址池获取的地址，

DHCP服务器会选择与接收DHCP请求报文的接口IPv4地址处于同一网段的地址池来进行分配。

问题 

SW4的vlanif30的IP地址配置错误导致，和R1无法通信，中继的数据报发不过去，获取不到地址