Cisco Catalyst 8500 series routers consist of the five-slot Cisco
Catalyst 8510 and the 13-slot Cisco Catalyst 8540. Originally, two models of
each system was offered:
Campus Switch Router (CSR)—Supported Layer-3 (L3) Ethernet, fast
Ethernet, and Gigabit Ethernet interfaces only.
Multiservice Switch Router (MSR)—Supported ATM interfaces only.
A single Cisco Catalyst 8540 now supports both Ethernet and ATM
interfaces in a single chassis when used with an ATM Router Module
This document clarifies the differences between the MSR model and CSR
model of the Cisco Catalyst 8540. It starts with a brief description of the
architecture of CSR and MSR and then explains how to use the L3 ATM module in
the same system. The last section contains a comparison table of CRS versus
There are no specific requirements for this document.
This document is not restricted to specific software and hardware
For more information on document conventions, refer to the
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Cisco Catalyst 8540 CSR is designed to scale campus distribution and
core networks. This Slot-13 chassis also provides support for Layer 2 (L2)
bridging and L3 routing as well as future capabilities for ATM uplink capacity.
The Cisco Catalyst 8540 Switch Processor requires two slots, with a third slot
needed for redundancy. Should either of the switch processors fail, the third
will take over. One slot is required for the route processor, which handles
system management and control plane functions. A second route processor slot is
reserved for redundancy. The remaining eight slots are used for connectivity
modules. The C8541CSR-RP and C8542CSR-SP modules run L3 Cisco IOS® Software.
Cisco Catalyst 8540 MSR can be equipped with ARM functionality which
provides Ethernet-ATM and ATM-ATM bridging and routing capabilities. When the
ATM router module is installed, you can have both L3 and ATM technologies in
the same multiservice ATM switch router chassis.
The ARM enables the interworking or frame forwarding between ATM and
Ethernet interfaces in the same Cisco Catalyst 8540. Cisco IOS Software Release
12.0(4)W5(11a) introduced support for the ARM and for CSR modules in an MSR
chassis. For more information, refer to
Notes for the Catalyst 8540 MSR for Cisco IOS Release 12.0(10)W5(18c).)
An MSR chassis is defined as a system with the MSR switch processor and route
processor cards. (See Table 1 for part numbers.)
If a system uses Ethernet modules only, load the CSR software image on
the MSR processor cards. The MSR processors support all CSR modules except the
ATM Uplink with Enhanced Gigabit Ethernet interface module (C85-1OC12 and
C85-1OC3). For more information, refer to the
and Software Compatibility Matrix.
Although they share the same chassis and reserve the five middle slots
for processor cards, the MSR and CSR systems use different sets of switch
processor cards and different images. The following table lists the key
functional differences between a Cisco Catalyst 8540 MSR and CSR system.
Table 1: Cisco 8540 CSR vs. MSR
Provides integrated ATM cell switching and L3 frame switching
and routing in a single chassis. Support both modules types in a single chassis
with the ARM.
Provides a multiservice ATM switch with circuit emulation,
inverse multiplexing over ATM (IMA) and Frame Relay interworking interfaces.
Provides L3 Ethernet features.
Provides ATM and Packet over SONET (POS) uplinks for connecting
to high-speed campus and metropolitan-area networks.
Route Processor Model
Switch Processor Model
Cisco IOS Images
Supported Interface Modules
All MSR and CSR interfaces except the ATM with enhanced Gigabit
All CSR modules (with a cat8540c image)
Support for Network Clock Module
Yes (with C8545MSR-MRP-MRP3CLK). Critical for timing-sensitive
applications, such as Circuit Emulation Services.
In other words:
With a C8541-RP route processor and C8542-SP switch processor, a
Cisco 8540 operates as a L3 switch only.
With a C8545-MRP multiservice route processor and C8546-MSP
multiservice switch processors, a Cisco 8540 operates as a multiservice ATM
switch that supports ATM, circuit emulation, IMA, and Frame Relay interworking
With an ARM and supporting Cisco IOS image, an 8540 with C8545-MRP
and C8546-MSP supports both ATM and L3 interfaces in a single chassis.
Note: Although the MSR processors support a Cisco IOS "C" image and CSR
processors support an "M" image, such configurations are not recommended or
supported. For more information, refer to the
and Software Compatibility Matrix for officially supported