Technical data

BLADE OS 5.1 Application Guide
BMD00136, November 2009 Chapter 8: Basic IP Routing
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To enable DHCP on an IP interface, use the following commands:
DHCP Relay Agent
DHCP is described in RFC 2131, and the DHCP relay agent supported on G8000s is described in
RFC 1542. DHCP uses UDP as its transport protocol. The client sends messages to the server on
port 67 and the server sends messages to the client on port 68.
DHCP defines the methods through which clients can be assigned an IP address for a finite lease
period and allowing reassignment of the IP address to another client later. Additionally, DHCP
provides the mechanism for a client to gather other IP configuration parameters it needs to operate
in the TCP/IP network.
In the DHCP environment, the G8000 acts as a relay agent. The DHCP relay feature enables the
switch to forward a client request for an IP address to two BOOTP servers with IP addresses that
have been configured on the switch.
When a switch receives a UDP broadcast on port 67 from a DHCP client requesting an IP address,
the switch acts as a proxy for the client, replacing the client source IP (SIP) and destination IP (DIP)
addresses. The request is then forwarded as a UDP Unicast MAC layer message to two BOOTP
servers whose IP addresses are configured on the switch. The servers respond as a UDP Unicast
message back to the switch, with the default gateway and IP address for the client. The destination
IP address in the server response represents the interface address on the switch that received the
client request. This interface address tells the switch on which VLAN to send the server response to
the client.
To enable the G8000 to be the BOOTP forwarder, you need to configure the DHCP/BOOTP server
IP addresses on the switch. Generally, you should configure the switch IP interface on the client side
to match the client’s subnet, and configure VLANs to separate client and server subnets. The DHCP
server knows from which IP subnet the newly allocated IP address should come.
In G8000 implementation, there is no need for primary or secondary servers. The client request is
forwarded to the BOOTP servers configured on the switch. The use of two servers provide failover
redundancy. However, no health checking is supported.
RS G8000 (config)# interface ip 2
RS G8000 (config-ip-if)# dhcp enable
RS G8000 (config-ip-if)# exit