H3C Technologies H3C S7500E Series Switches - Manual (Page 70)

6-5
To do… Use the command… Remarks
Enter system view system-view —
Create a DHCP server group and
add a server into the group
dhcp relay server-group group-id ip
ip-address
Required
Not created by default.
Enter interface view
interface interface-type
interface-number
—
Correlate the DHCP server group
with the current interface
dhcp relay server-select group-id
Required
By default, no interface is
correlated with any DHCP
server group.
z You can specify up to twenty DHCP server groups on the relay agent and up to eight DHCP server
addresses for each DHCP server group.
z The IP addresses of DHCP servers and those of relay agent’s interfaces cannot be on the same
subnet. Otherwise, the client cannot obtain an IP address.
z A DHCP server group can correlate with one or multiple DHCP relay agent interfaces, while a
relay agent interface can only correlate with one DHCP server group. Using the dhcp relay
server-select command repeatedly overwrites the previous configuration. However, if the
specified DHCP server group does not exist, the interface still uses the previous correlation.
z The group-id argument in the dhcp relay server-select command is configure by using the dhcp
relay server-group command.
Configuring the DHCP Relay Agent Security Functions
Creating static bindings and enabling IP address check
For avoidance of invalid IP address configuration, you can configure the DHCP relay agent to check
whether a requesting client’s IP and MAC addresses match a binding (dynamic or static) on the DHCP
relay agent.
With this feature enabled, the DHCP relay agent can dynamically record clients’ IP-to-MAC bindings
after clients get IP addresses. It also supports static bindings, that is, you can manually configure
IP-to-MAC bindings on the DHCP relay agent, so that users can access external networks using fixed
IP addresses.
Upon receiving an ARP packet, the DHCP relay agent matches the sender’s IP and MAC addresses in
the packet against the bindings (both dynamic and static). If no match is found, the DHCP relay agent
does not learn the ARP entry, and thus the sending host cannot access external networks via the
DHCP relay agent.
Follow these steps to create a static binding and enable IP address check: