D-Link DWS-4026 Product Manual - Page 182

D-Link Unified Access System Software User Manual 12/10/09 Field Client Ifc Mismatch DHCP Server Msgs Received Table 92: DHCP Snooping Statistics Description The number of DHCP messages that are dropped based on the source MAC address and client hardware address verification. The number of server messages that are dropped on an untrusted port. • Click Clear Stats to clear all interface statistics. CONFIGURING DHCP L2 RELAY When a DHCP client and server are in the same IP subnet, they can directly connect to exchange IP address requests and replies. However, having a DHCP server on each subnet can be expensive in and is often impractical. Alternatively, network infrastructure devices can be used to relay packets between a DHCP client and server on different subnets. Such a device, a Layer 3 Relay agent, is generally a router that has IP interfaces on both the client and server subnets and can route between them. However, in Layer 2 switched networks, there may be one or more infrastructure devices (for example, a switch) between the client and the L3 Relay agent/DHCP server. In this instance, some of the client device information required by the L3 Relay agent may not be visible to it. In this case, an L2 Relay agent can be used to add the information that the L3 Relay Agent and DHCP server need to perform their roles in address and configuration and assignment. Before it relays DHCP requests from clients, the switch can add a Circuit ID and a Remote ID. These provide information about the circuit and port number connected to the client. This information is added as suboptions in the DHCP Option 82 packets (see sections 3.1 and 3.2 of RFC3046). The switch removes this option from packets that it relays from L3 Relay agents/DHCP servers to clients. These sub-options may be used by the DHCP server to affect how it treats the client, and also may be used by the relay agent to limit broadcast replies to the specific circuit or attachment point of the client. The Switching > DHCP Snooping > DHCP L2 Relay folder provides access to the following pages: • "DHCP L2 Relay Global Configuration" • "DHCP L2 Relay Interface Configuration" • "DHCP L2 Relay VLAN Configuration" • "DHCP L2 Relay Interface Statistics" DHCP L2 Relay Global Configuration Use this page to enable or disable the switch to act as a DHCP L2 relay agent. This functionality must also be enabled on each port you want this service to operate on (see "DHCP L2 Relay Interface Configuration" on page 183). The switch can also be configured to relay requests only when the VLAN of the requesting client corresponds to a service provider's VLAN ID that has been enabled with the L2 DHCP relay functionality (see "DHCP L2 Relay VLAN Configuration" on page 184). To access this page, click LAN > L2 Features > DHCP Snooping > DHCP L2 Relay > Global Configuration. Page 182 Configuring DHCP Snooping Document 34CSFP6XXUWS-SWUM100-D7