Brocade Network OS Administrator’s Guide v4.1.1 - Manual (Page 476)

NOTE
The Brocade VDX 6740 series platforms support only two PFCs.
Ethernet Priority Flow Control includes the following features:
• Everything operates exactly as in Ethernet Pause described above, except there are eight high-
water and low-water thresholds for each input port. This means queue levels are tracked per input
port plus priority.
• Pause On/Off can be specified independently for TX and RX directions per priority.
• Pause time programmed into Ethernet MAC is a single value covering all priorities.
• Both ends of a link must be configured identically for Ethernet Pause or Ethernet Priority Flow
Control because they are incompatible.
Multicast rate limiting
Multicast rate limiting provides a mechanism to control multicast frame replication and cap the effect of
multicast traffic.
Multicast rate limit is applied to the output of each multicast receive queue. Rate limits apply equally to
ingress receive queuing (first-level expansion) and egress receive queuing (second-level expansion),
because the same physical receive queues are utilized. You can set policies to limit the maximum
multicast frame rate differently for each traffic class level and cap the total multicast egress rate out of
the system.
Multicast rate limiting includes the following features:
• All configuration parameters are applied globally. Multicast rate limits are applied to multicast
receive queues as frame replications are placed into the multicast expansion queues. The same
physical queues are used for both ingress receive queues and egress receive queues, so rate limits
are applied to both ingress and egress queuing.
• The rate limit value represents the maximum multicast expansion rate in packets per second (pps).
NOTE
Multicast rate limiting is not supported on Brocade VDX 8770-4 and 8770-8 platforms. For these
products, refer to
BUM storm control on page 476.
BUM storm control
A traffic storm occurs when packets flood the LAN, creating excessive traffic and degrading network
performance. Broadcast, unicast, and unknown multicast (BUM) storm control can prevent disruptions
on Layer 2 physical ports.
BUM storm control allows you to limit the amount of broadcast, unknown unicast, and multicast
ingress traffic on a specified interface or on the entire system. All traffic received in excess of the
configured rate gets discarded. You also have the option to specify whether to shut down an interface
if the maximum defined rate is exceeded within a five-second sampling period. When a port is shut
down, you receive a log message. You must then manually re-enable the interface by using the no
shut command.
BUM storm control considerations and limitations
• BUM storm control must be configured on one of the following physical interfaces:
Multicast rate limiting
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