Understanding Filter-Based Forwarding
You can use firewall filters in conjunction with virtual routing instances to specify different routes for packets to travel in their networks. To set up this feature–called filter-based forwarding–you specify a filter and match criteria and then specify the virtual routing instance to send packets to.
You might want to use filter-based forwarding to route specific types of traffic through a firewall or other security device before the traffic continues on its path. You can also use filter-based forwarding to give certain types of traffic preferential treatment. For example, you might want to ensure that the highest-priority traffic is forwarded over a 40-Gigabit Ethernet link. You might also use filter-based forwarding to obtain more control over load balancing than dynamic routing protocols provide.
 | Note: You can create as many as 128 filters or terms that direct packets to a given virtual routing instance. |
Filters used for filter-based forwarding consume memory in two ternary content addressable memories (TCAMs), and this affects the number of supported filters. See Planning the Number of Firewall Filters to Create and Understanding FIP Snooping, FBF, and MVR Filter Scalability for more information. The section FBF Filter VFP TCAM Consumption in the latter topic specifically addresses the number of supported filters when using filter-based forwarding.
