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ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter 16 Configuring Tag Switching and MPLS
Configuring Label Edge Routing
be selected based upon the CoS value in the incoming label or ToS in the IP packet. The enhanced ATM
router module (ARM) serves as the proxy interface for every incoming and outgoing ATM interface (that
is linked to an Enhanced ATM router module using the mpls-forwarding command) in the LSP path to
do the MPLS packet processing. To enable LER functionality, you must first configure tag switching on
an ATM interface and link the ATM interface to an ATM router module for MPLS packet processing.
For more information on configuring MPLS on ATM interfaces, refer to “Configuring Tag Switching”
in the ATM Switch Router Software Configuration Guide. For more information on configuring MPLS
on Ethernet interfaces, refer to “Configuring Tag Switching” in the Layer 3 Switching Software and
Feature Configuration Guide.
LER Software Limitations
The following restrictions apply to LER on the Cisco Catalyst 8540:
• The ATM interface (only main interface) can be linked with only the enhanced ATM router module
main interface.
• VRF configuration on ATM OC-x interfaces is not supported.
• The COS, LFIB, and Label region in the SDM can be modified using the sdm sram command. But,
the changes only take effect after a switch reload.
• Load Balancing between provider edge (PE) and provider (P) switches is not supported.
• The SDM SRAM size for LFIB, Label Rewrite, and Label COS region does not increase
dynamically when the number of entries increase.
Note To change SDM SRAM configuration you must use the sdm size configuration command
and the reload command to reconfigure the memory and then halt and perform a cold restart
of the switch.
• Packet counters are not implemented for MPLS traffic.
• Forwarding of VPN traffic is based only on the VPN routing table and not on the global routing
table. If the VPN routing table lookup fails, the packets will be discarded.
• The Enhanced ATM router module internal link has a maximum capacity of 1.2 Gbps which could
affect the number of interfaces—either Fast Ethernet or ATM—associated with the Enhanced ATM
router module.
• Only 2k terminating TAG VCs are supported per controlling Enhanced ATM router module
hardware interface.
• Fragmentation based on MTU for IP to MPLS and MPLS to MPLS traffic is implemented in the
route processors not on the interface modules.