Scenario One: DHCP Helper with FWSM 1.1(x)
When running release 1.1(x), the FWSM drops incoming UDP broadcasts. Protocols such as DHCP (RFC 2131) rely on such packets extensively, and the lack of DHCP helper functionality in the FWSM can be problematic in certain designs. This section explains how the multiple VLAN interfaces can work around that shortcoming. Take a look at the sample topology depicted in Figure 4-9. Suppose two hosts on VLAN 30 (inside screened subnet) would like to acquire an IP address using DHCP. The enterprise's DHCP server is located off another screened subnet on VLAN 10. VLAN 20 represents the outside network and binds the MSFC to the FWSM. Finally, VLAN 500 connects the Catalyst 6500 switch to the "outside world."