3com S7906E Manuel De Montage

 

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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 network using fixed IP addresses. 

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. If not, the client cannot access outside networks via the DHCP relay agent. 

Follow these steps to create a static binding and enable IP address check: 

Enter system view 

— 

Create a static binding 

dhcp relay security static 
ip-address mac-address 
[ interface interface-type 
interface-number ] 

Optional 

No static binding is created 
by default. 

Enter interface view 

interface interface-type 
interface-number 

— 

Enable invalid IP address check 

dhcp relay address-check 
{ disable | enable } 

Required 

Disabled by default. 

 

z 

The  dhcp relay address-check enable command is independent of other commands of the 

DHCP relay agent. That is, the invalid address check takes effect when this command is executed, 

regardless of whether other commands are used. 

z 

The dhcp relay address-check enable command only checks IP and MAC addresses of clients. 

z 

You are recommended to configure IP address check on the interface enabled with the DHCP relay 

agent; otherwise, valid DHCP clients may be denied from accessing networks.  

z 

When using the dhcp relay security static command to bind an interface to a static binding entry, 

make sure that the interface is configured as a DHCP relay agent; otherwise, address entry 

conflicts may occur. 

 

Via the DHCP relay agent, a DHCP client sends a DHCP-RELEASE unicast message to the DHCP 

server to relinquish its IP address. In this case the DHCP relay agent simply conveys the message to 

the DHCP server, thus it does not remove the IP address from dynamic client entries. To solve this 

problem, the periodic refresh of dynamic client entries feature is introduced. 

With this feature, the DHCP relay agent uses the IP address of a client and the MAC address of the 

DHCP relay interface to periodically send a DHCP-REQUEST message to the DHCP server.