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Routing between VLANs

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would you want to run this on 10BaseT because it is processor and band-
width intensive.

There are some really nice high-end routers that provide multi-layer

switching by communicating to a NetFlow Feature Card (NFFC) in the
Cisco Catalyst 5000 series of switches. The routers must have the IOS ver-
sions of 11.3.4 or later and run the MultiLayer Switch Protocol (MLSP). The
routers that support this are the 7500, 7200, 4500, and 4700 series of routers.

Route Switch Modules (RSMs)

Route Switch Modules (RSMs)

are also called

internal route processors

because the processing of layer 3 packets is internal to a switch. You need to
add an RSM to a layer 2 device--for example, a 5000 Catalyst switch--to be
able to provide switching of layer 3 packets without a router.

An RSM makes layer 2 switches a multi-layer switch and can integrate

layer 2 and layer 3 functionality in a single box. The 5000 series uses the
RSM or a

Route Switch Feature Card (RSFC)

, and the 6000 series uses the

Multilayer Switch Module (MSM) to perform this function. The RSM,
RSFC, and MSM are configured in exactly the same way on the switch.

The RSM is a module plugged directly into the switch, which runs the

Cisco IOS in order to perform inter-VLAN communication. The 5000 series
switch sees the RSM as a single trunked port and a single MAC address. In
other words, it appears as a router on a stick to the switch. The RSM inter-
face to the switch is through VLAN 0 and VLAN 1. VLAN 0 is not accessible
to the administrator. The RSM uses two channels, and VLAN 0 maps to
channel 0, which supports communication between the RSM and the Cata-
lyst 5000 series default VLAN (VLAN 1). VLAN 1 maps to channel 1. The
MAC address assigned to the RSM is from the Programmable Read Only
Memory (PROM) on the line communication processor (LCP). This MAC
address is used to identify the slot of the RSM and for diagnostics. The MAC
addresses for VLAN 1 are assigned from a PROM that contains 512 MAC
addresses. All routing interfaces except VLAN 0 use the base MAC address.

The RSFC is a daughter card for the Supervisor Engine II G and Supervi-

sor III G cards. The RSFC is a fully functioning router running the Cisco IOS.

The MSM uses four full-duplex Gigabit Ethernet interfaces to connect to

the switch and looks like an external router to the switch. These four inter-
faces can be four separate links for four different VLANs, or they can be

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