Brocade TurboIron 24X Series Configuration Guide - Manual (Page 523)

Brocade TurboIron 24X Series Configuration Guide 489
53-1003053-01
Configuring IP parameters – Layer 2 Switches
For example, in Figure 61 , a host from each of the four subnets supported on a Layer 2 Switch
requests an IP address from the DHCP server. These requests are sent transparently to the router.
Because the router is unable to determine the origin of each packet by subnet, it assumes the
lowest IP address or the ‘primary address’ is the gateway for all ports on the Layer 2 Switch and
stamps the request with that address.
When the DHCP request is received at the server, it assigns all IP addresses within that range only.
With DHCP Assist enabled on a Layer 2 Switch, correct assignments are made because the Layer 2
Switch provides the stamping service.
How DHCP Assist works
Upon initiation of a DHCP session, the client sends out a DHCP discovery packet for an address
from the DHCP server as seen in
Figure 62 . When the DHCP discovery packet is received at a Layer
2 Switch with the DHCP Assist feature enabled, the gateway address configured on the receiving
interface is inserted into the packet. This address insertion is also referred to as stamping.
FIGURE 62 DHCP requests in a network with DHCP Assist operating on a Switch