Leaflet

OL-11615-01

MTU Failure (Unicast and Multicast)

Similar to the TTL failure rate limiter, the rate limiter for MTU failures is supported for both unicast and

multicast traffic. Packets that fail an MTU check are sent to the MSFC CPU. This might cause the MSFC

to be overwhelmed.

This rate limiter is disabled by default. To enable and set the MTU Failure rate limiter, use the mls

rate-limit all mtu-failure command.

Router(config)# mls rate-limit all mtu-failure

pps

[

packets-in-burst

]

This example shows how to rate limit packets failing the MTU failures from being sent to the MSFC to

10000 pps with a burst of 10:

Router(config)# mls rate-limit all mtu-failure 10000 10

Note Do not use this rate limiter in conjunction with Layer 2 multicast in a system with PFC3A.

For more information on the mls rate-limit all mtu-failure command, refer to the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/122sx/cmdref/m1.htm#wp1497651

Layer 2 PDU

The Layer 2 protocol data unit (PDU) rate limiter allows you to limit the number of Layer 2 PDU

protocol packets (including BPDUs, DTP, PAgP, CDP, STP, and VTP packets) destined for the supervisor

engine and not the MSFC CPU. You cannot enable the Layer 2 PDU rate limiter if the Catalyst 6500

Series switch is operating in truncated mode. The switch uses truncated mode for traffic between

fabric-enabled modules when there are both fabric-enabled and nonfabric-enabled modules installed. In

this mode, the switch sends a truncated version of the traffic (the first 64 bytes of the frame) over the

switch fabric channel.

This rate limiter is disabled by default. To enable and set the Layer 2 PDU rate limiter, use the mls

rate-limit layer2 pdu command.

Router(config)# mls rate-limit layer2 pdu

pps

[

packets-in-burst

]

This example shows how to rate limit Layer 2 PDUs to 20000 pps with a burst of 20 packets:

Router(config)# mls rate-limit layer2 pdu 20000 20

For more information on the mls rate-limit layer2 pdu command, refer to the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/122sx/cmdref/m1.htm#wp1729104

Layer 2 Protocol Tunneling

This rate limiter limits the Layer 2 protocol tunneling packets, which include control PDUs, CDP, STP,

and VTP packets destined for the supervisor engine. These packets are encapsulated in software

(rewriting the destination MAC address in the PDU), and then forwarded to a proprietary multicast

address (01-00-0c-cd-cd-d0). You cannot enable the Layer 2 Protocol Tunneling rate limiter if the

Catalyst 6500 Series switch is operating in truncated mode. The switch uses truncated mode for traffic

between fabric-enabled modules when there are both fabric-enabled and nonfabric-enabled modules

installed. In this mode, the switch sends a truncated version of the traffic (the first 64 bytes of the frame)

over the switch fabric channel.