Hardware Rate Limiters

The hardware rate limiters are primarily used to control traffic where an ACL cannot be used. Examples of this are IP options, Time to Live (TTL), and maximum transmission unit (MTU) failures, and other special cases.

It is possible to specify up to 32 different rate limiters, but some of them share one of the physical rate limiters. Ten physical rate limiters are available, 2*[Layer 2] and 8*[General/ Unicast/Multicast]. To see which hardware rate limiters are active, use the command shown in Example 13-1.

Example 13-1 Displaying Default Hardware Rate-Limiter Values

c6500#sh mls rate-limit
Sharing Codes: S - static, D		dynamic
Codes dynamic sharing:	H - owner		(head)	of the	group, g	- guest of the group
Rate Limiter Type	Status		Packets/s		Burst	Sharing
MCAST NON RPF	Off
MCAST DFLT ADJ	On			100000	100	Not sharing
MCAST DIRECT CON	Off
ACL BRIDGED IN	Off
ACL BRIDGED OUT	Off
IP FEATURES	Off
ACL VACL LOG	Off
CEF RECEIVE	Off
CEF GLEAN	Off
MCAST PARTIAL SC	On			100000	100	Not sharing
IP RPF FAILURE	On			10000	10	Group:0 S
TTL FAILURE	Off
ICMP UNREAC. NO-ROUTE	On			10000	10	Group:0 S
ICMP UNREAC. ACL-DROP	On			0	0
ICMP REDIRECT	Off
MTU FAILURE	Off
MCAST IP OPTION	Off
UCAST IP OPTION	Off
LAYER_2 PDU	Off
LAYER_2 PT	Off
IP ERRORS	On			10000	10	Group:0 S
CAPTURE PKT	Off
MCAST IGMP	Off
MCAST IPv6 DIRECT CON	Off
MCAST IPv6 ROUTE CNTL	Off
MCAST IPv6 *G M BRIDG	Off
MCAST IPv6 SG BRIDGE	Off
MCAST IPv6 DFLT DROP	Off
MCAST IPv6 SECOND. DR	Off
MCAST IPv6 *G BRIDGE	Off
MCAST IPv6 MLD	Off
IP ADMIS. ON L2 PORT	Off

To change the values of these rate limiters, use the mls rate-limit command. For example, to limit the number of packets per second that would be dropped because of TTL expiry, use the following command:

C6500(config)#mls rate-limit all ttl-failure 10

The mls rate-limit command sets the allowed packets per second (pps) value to 10, but it also sets the additional burst value to 10 pps. You can manually change the burst value by specifying an optional parameter after the initial pps value.

Continue reading here: Configuring Software Based CoPP

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