DCHP Relay Snooping Mode Introduction
7-9
Software Reference for SwitchBlade x3100 Series Switches (Network Management)
7.2.4 DCHP Relay Snooping Mode
DHCP Snooping is a configurable option for each DHCP Relay instance. In Relay mode, the DHCP Relay Agent
allows the Allied Telesis system to intercept the broadcast DHCP messages and forward the messages as uni-
cast. On the contrary, the Snooping mode allows the system to keep the DHCP messages as broadcast for
DHCP clients/servers that are on the same network. The client or an upstream device is used as the relay
agent.
Refer to Figure 7-4 for an example configuration.
7.2.4.1 Client Requesting an IP Address (Dynamically Allocated)
•
Steps 1 and 2 are the same as in 7.2.2.1.
• Subsequent steps are:
1. DHCP Snooping leaves the “all networks broadcast address” in the IP destination field of the packet.
2. The DHCP Snooping agent floods the DHCP packet out all NETWORK interfaces that are members of the
VLAN.
7.2.4.2 Receiving Requests from the DHCP Server
The steps are the same as in 7.2.2.2.
7.2.4.3 Configuration Rules
•
The VLAN type used, either upstream forwarding only (UFO) or standard, since the DHCP packets are
flooded only on
NETWORK interfaces
• The upstream router must be configured with a DHCP relay agent since it must route the broadcast DHCP
message to the correct set of servers, or the servers must be on the same network.
• If IP Filtering is set to ON for an interface, there is a limit of eight VLANs that can participate in DHCP Relay
mode on that interface.
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