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proprietary protocol transfers the FIB information to a NetFlow Feature Card (NFFC or NFFC II) on a Cisco
Catalyst 5000 series, or to another forwarding board or module on the higher−speed Cisco distributed
switches.
There is little difference between using an external router and an internal route processor as your source of the
FIB to route Layer 3 protocol data traffic or to perform inter−VLAN routing; it is basically a design choice. If
you need to route using an external router, keep cost and speed in mind as you decide which router is best. In
the Immediate Solutions sections, we will walk through configuring a Cisco 2600 for trunking, which allows
for inter−VLAN routing. Let’s look at how to decide whether to use an internal or external route processor:
Cisco 2600 series—A good choice if you just need to do inter−VLAN routing.•
Cisco 3600 series—A good choice if you need to do inter−VLAN routing a little more quickly. You
can use the 3600 as a path determination engine and use an NFFC or equivalent on the switch.
•
Route Switch Module—If you need to handle routing very quickly, use an RSM with an NFFC or
equivalent, such as the RSFC, MSM, or Multilayer Switch Feature Card (MSFC).
•
Cisco 10000 or 12000—A good choice if you need to route huge amounts of data very quickly,
especially if you have multiple WAN interfaces. If you need to use an external route processor
because of a lack of open slots on your switch, a Cisco 7200 or 7500 might be a good alternative.
•
You can configure one or more Hot Standby Routing Protocol (HSRP) groups on an external route processor
or on internal route processor interfaces such as the RSM or the RSFC VLAN interfaces. This protocol
(discussed in more detail in Chapter 12) provides a way to transparently create redundant Layer 3 routing
devices in the network. Interfaces in an HSRP group share the same virtual IP and MAC addresses. You
configure all the devices’ default gateway addresses to the virtual IP address assigned to the HSRP−enabled
router’s interface. In the event of a failure of a link to one device or a failure of one router interface, the other
takes over so service is not interrupted.
Multimodule vs. Fixed Configuration Switches
So far, we have talked about the internal route processors and their features. Several Cisco switches, such as
the Catalyst 4000, 5000, 6000, 8500, and 12000 families of switches, are considered multimodule switches.
Many Layer 3 switches, such as the Cisco Catalyst 2926G−L3, 2948G−L3, and 4912G, do not have internal
cards. Instead, these switches have built−in modules and are considered logically modular switches or fixed
configuration switches. The Catalyst 2926G has 24 ports of 10/100 Fast Ethernet and 2 ports of Gigabit
Ethernet built in. The ports are considered to be located on module 2 logically, although the module cannot be
removed from the switch like an add−on card.
On an internal or external route processor, each interface can be divided into many subinterfaces. Doing so
creates a flexible solution for routing streams of multiple data types through one interface. On each switch
interface connected to a route processor’s interface, you need to identify the VLAN encapsulation method and
assign an IP address and subnet mask to the interface.
Now, let’s look at the features of the internal route processors.
Available Route Processors
When a switch receives a packet from a port on one VLAN destined for the port of another VLAN, the switch
must find a path on which to send the frame. Because switches are designed to isolate traffic to collision
domains or subnets, they cannot by default forward data to another VLAN or network without some other
device’s intervention to route the data and create routing tables of networks and devices.
As you learned in the previous section, route processors can be used to route data between foreign VLANs
and other logically segmented parts of the network, such as subnets. They also route data to remote WAN
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