Align Numbers of VLAN Subinterfaces with Physical
For consistency, align the VLAN subinterface
numbers with the physical interface numbers they serve. For example,
interface vlan.1 serves DHCP for the network attached to ethernet1/1.
This allows you to associate them with each other faster and troubleshoot
issues more easily later.
Conserve IP Addresses for VLAN Subinterfaces
production IP address space is used for the VLAN interfaces, giving
them IP addresses with 32-bit netmasks will conserve address space.
You can use addresses from a single network (for example, 184.108.40.206/24)
for all the VLAN interfaces. Because these interfaces exist solely
to serve DHCP to a local network, the addresses assigned to the
VLAN interfaces don’t need to be routable in the rest of the enterprise.
Operationally, this means that the same network space and addresses
can be used for VLAN interfaces on all firewalls in the enterprise.
Configure a Network Route to all VLAN Interfaces
configuring this solution for multiple interfaces, the routing configuration
changes slightly. On the default (production) virtual router, you
can configure a network route to the VLAN interfaces instead of
a collection of host routes. In the figure below all of the VLAN
interfaces have addresses that can be summarized using a 220.127.116.11/24
DHCP virtual router, add network routes for each network for which
a VLAN interface serves DHCP and set the default (production) virtual
router as the next hop. Adding network rather than host routes for
the DHCP relay agents allows the probe feature on the DHCP servers