When a packet is being multicast to two or more interfaces on the egress adapter card or block of fixed ports, or when a packet at port ingress is mirrored, one extra buffer per packet is used.
In previous releases, this extra buffer was not added to the queue count. When checking CBS during multicast traffic enqueuing, the CBS was divided by two to prevent buffer overconsumption by the extra buffers. As a result, during multicast traffic enqueuing, the CBS buffer limit for the queue was considered reached when half of the available buffers were in use.
As of Release 8.0 of the 7705 SAR, the CBS is no longer divided by two. Instead, the extra buffers are added to the queue count when enqueuing, and are removed from the queue count when the multicast traffic exits the queue. The full CBS value is used, and the extra buffer allocation is visible in buffer allocation displays.
When upgrading to Release 8.0 of the 7705 SAR, ensure that previous CBS and MBS configurations take extra buffers for multicast packets into account, and that maximum delay budgets are not affected adversely.