Dhcp Relay Configuration - Edge-Core ES4626 User Manual

no service dhcp
Function: Enables DHCP server; the "no service dhcp" command disables the DHCP
service.
Default: DHCP service is disabled by default.
Command mode: Global Mode
Usage Guide: Both DHCP server and DHCP relay are included in the DHCP service.
When DHCP services are enabled, both DHCP server and DHCP relay are enabled.
ES4626/ES4650 switch can only assign IP address for the DHCP clients and enable
DHCP relay when DHCP server function is enabled.
Example: Enabling DHCP server.
Switch(Config)#service dhcp

11.3 DHCP Relay Configuration

When the DHCP client and server are in different segments, DHCP relay is required
to transfer DHCP packets. Adding a DHCP relay makes it unnecessary to configure a
DHCP server for each segment, one DHCP server can provide the network configuration
parameter for clients from multiple segments, which is not only cost-effective but also
management-effective.
DHCPDiscover(Broadcast)
DHCPOFFER(Unicast)
DHCPREQUEST(Broadcast)
DHCPACK(Unicast)
DHCP Client
As shown in the above figure, the DHCP client and the DHCP server are in different
networks, the DHCP client performs the four DHCP steps as usual yet DHCP relay is
added to the process.
1. The client broadcasts a DHCPDISCOVER packet, and DHCP relay inserts its
own IP address to the relay agent field in the DHCPDISCOVER packet on
receiving the packet, and forwards the packet to the specified DHCP server (for
DHCP frame format, please refer to RFC2131).
2. On the receiving the DHCPDISCOVER packets forwarded by DHCP relay, the
DHCP server sends the DHCPOFFER packet via DHCP relay to the DHCP client.
3. DHCP client chooses a DHCP server and broadcasts a DHCPREPLY packet,
DHCP relay forwards the packet to the DHCP server after processing.
DHCP Relay
Fig 10-2 DHCP relay
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DHCPDiscover
DHCPOFFER
DHCPREQUEST
DHCPACK
DHCP Server