3550 configure a DHCP relay proxy instance

3550 dhcp configuration, many discussions on the network, but there are mostly errors and omissions, according to the configuration of an "IPHELPER-ADDRESSDHCP server address", the project found that the client can not get the IP address from the DHCP server, I recently configured 3550 as a DHCP server relay proxy. I was also confused for a long time. Later, I searched for information online and asked for help from the forum. I finally passed the test in the project, in order to avoid such problems in the project, we need to adjust the configuration process left and right for your reference.
Network Environment: A 3550EMI switch is divided into three VLANs. vlan2 is the network where the server is located, named server, IP address segment is 192.168.2.0, subnet mask: 255.255.255.0, Gateway: 192.168.2.1, the Domain Server is windows2000advanceserver and also serves as a DHCP server. The DNS server has the IP address 192.168.2.10, vlan3 is the network where client 1 is located, the IP address segment is 192.168.3.0, The subnet mask is 255.255.255.0, And the Gateway: 192.168.3.1 is named work01, vlan4 is the network of client 2, work02, IP address segment is 192.168.4.0, subnet mask: 255.255.255.0, Gateway: 192.168.4.1.
Ports 1-8 on 3550 are allocated to VLAN2, ports 9-16 are divided into VLAN3, and ports 17-24 are allocated to VLAN4.
The configuration command and steps are as follows:
Step 1: Create a VLAN:
Switch> VlanDatabase
Switch (Vlan)> Vlan2Nameserver
Switch (Vlan)> Vlan3Namework01
Switch (vlan)> Vlan4Namework02
Step 2: enable DHCP relay Proxy:
/* In the key step, if the following two commands are missing, use "IPHELPER-ADDRESSDHCP server address" in the VLAN to specify the DHCP server, the client still cannot obtain the IP address */
Switch> Enable
Switch # Configt
Switch (Config) ServiceDhcp
Switch (Config) IpDhcpRelayInformationOption
Step 3: Set the VLANIP address:
Switch (Config)> IntVlan2
Switch (Config-vlan) IpAddress192.168.2.1255.255.255.0
Switch (Config-vlan) NoShut
Switch (Config-vlan)> IntVlan3
Switch (Config-vlan) IpAddress192.168.3.1255.255.255.0
Switch (Config-vlan) NoShut
Switch (Config-vlan)> IntVlan4
Switch (Config-vlan) IpAddress192.168.4.1255.255.255.0
Switch (Config-vlan) NoShut
Switch (Config-vlan) Exit
/* Note: Because the ports are not configured to VLAN2, 3, 4 at this time, each VLAN will be DOWN. After the ports are allocated to each VLAN, the VLAN will get up */
Step 4: set global port Parameters
Switch (Config) InterfaceRangeFa0/1-24
Switch (Config-if-range) SwitchportModeAccess
Switch (Config-if-range) Spanning-treePortfast
Step 5: add the port to VLAN2, 3, 4
/* Add Port 1-8 to VLAN2 */
Switch (Config) InterfaceRangeFa0/1-8
Switch (Config-if-range) SwitchportAccessVlan2
/* Add Port 9-16 to VLAN3 */
Switch (Config) InterfaceRangeFa0/9-16
Switch (Config-if-range) SwitchportAccessVlan3
/* Add Port 17-24 to VLAN4 */
Switch (Config) InterfaceRangeFa0/17-24
Switch (Config-if-range) SwitchportAccessVlan4
Switch (Config-if-range) Exit
/* After this step, each VLAN will get up */
Step 6: Set the DHCP server address in VLAN3 and 4
/* No DHCP server address must be specified in VLAN2 */
Switch (Config) IntVlan3
Switch (Config-vlan) IpHelper-address192.168.2.10
Switch (Config) IntVlan4
Switch (Config-vlan) IpHelper-address192.168.2.10
Step 7: Enable Routing
/* After a route is enabled, the hosts in each VLAN can access each other. To further control the access permission, apply the access control list */
Switch (Config) IpRouting
Step 8: end and save the configuration
Switch (Config-vlan) End
Switch # CopyRunStart