Administrator's Guide v4.1.1 Manual

Configuring IP DHCP Relay
● DHCP protocol.............................................................................................................. 649
● IP DHCP Relay function................................................................................................649
● Brocade IP DHCP Relay overview................................................................................650
● Configuring IP DHCP Relay.......................................................................................... 651
● Displaying IP DHCP Relay addresses for an interface................................................. 654
● Displaying IP DHCP Relay addresses on specific switches......................................... 655
● Displaying IP DHCP Relay statistics............................................................................. 657
● Clearing IP DHCP Relay statistics................................................................................ 658
● VRF support.................................................................................................................. 658
● High availability support................................................................................................ 660
DHCP protocol
Dynamic Host Configuration Protocol (DHCP) is an IP network protocol that provides network
configuration data, such as IP addresses, default routes, DNS server addresses, access control, QoS
policies, and security policies stored in DHCP server databases to DHCP clients upon request.
You can enable DHCP service on VDX switches so that they can automatically obtain an Ethernet IP
address, prefix length, and default gateway address from the DHCP server. Refer to Configuring an
IPv4 address with DHCP on page 68 for more information.
IP DHCP Relay function
DHCP relays are an important feature for large networks as they allow communication between DHCP
servers and clients located on different subnets.
In small networks with only one IP subnet, DHCP clients can communicate directly with DHCP servers.
Clients located on a different subnet than the DHCP server cannot communicate with that server
without obtaining an IP address with appropriate routing information.
By installing a DHCP relay agent on different subnets in a large network, broadcast DHCP packets can
be forwarded from a DHCP client to locate a DHCP server on a remote subnet. The relay agent’s IP
address is stored in the gateway IP address (GIADDR) field of the DHCP packet, The DHCP server
uses the GIADDR field to find the subnet where the relay agent received the broadcast, and then
assigns IP addresses to that subnet. The DHCP server replies to the client with a unicast message to
the GIADDR address and the relay agent will forward the response to the local network.
Network OS Administrator’s Guide
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