BigIron RX Series Configuration Guide 50153-1001986-01Configuration considerations 19The running total can never exceed the maximum credit total. When packets arrive at the port, aclass is assigned to the packet, based on the rate limiting policies. If the running total of the class isless than the size of the packet, then the packet is dropped. Otherwise, the size of the packet issubtracted from the running total and the packet is forwarded. If there is no traffic that matchesrate limiting criteria, then the running total can increase until it reaches the maximum credit total.Configuration considerations• Except for port-based rate limiting policies, all rate limiting policy types can be applied only toinbound ports on the device.• Only one type of inbound rate limiting can be applied on a physical port. For example, youcannot apply inbound port-and-ACL-based and inbound port-based rate limiting policies on thesame port.• Outbound port-based rate limiting policy can be combined with any type of inbound ratelimiting policy.• Any VLAN-based rate limiting can limit only tagged packets that match the VLAN ID specified inthe policy. Untagged packets are not subject to rate limiting.• The minimum configurable rate limiting rate in the BigIron RX is 20,345 bps. The maximumconfigurable rate limiting rate is near line-rate.• Control packets are not subject to rate limiting.• Trunks with rate-limiting on their physical members is configurable where all the ports inheritthe rate-limiting policy.• The device currently only support "strict" and "destination-weighted" scheduling schemes. (qosscheduler ..) on the 16x10G card.• Certain features such as FDP, CDP, UDLD and LACP that make the port run in dual mode cancause traffic to be rate limited to less than the expected requested rate. When the port is indual-mode, all incoming or outgoing packets are treated as tagged. An extra 4 bytes is addedto the length of the packet to account for the tag, thus causing the requested rate to be lessthan the expected requested rate. Ports in dual mode are assumed to be tagged ports for ratelimiting purpose.• The CAM can hold up to 1024 ACL, PBR, and Rate Limiting entries and this maximum is dividedas follows:• ACL – 416 entries• Rate Limiting – 416, entries shared with PBRAlso note:• Port-based and VLAN-based rate limiting policies consume one CAM entry per policy.• ACL-based rate limiting policies consume entries based on the number of statements in anACL.• See the limits in Table 98.
