Converged Enhanced Ethernet Administrator’s Guide 101
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Multicast rate limiting 9
DRAFT: BROCADE CONFIDENTIAL

Ethernet Priority Flow Control

Ethernet Priority Flow Control (PFC) is a basic extension of the Ethernet Pause. The Pause MAC
control message is extended with eight 2-byte pause numbers and a bitmask to indicate which
values are valid. Each pause number is interpreted identically to the base Pause protocol; however
each is applied to the corresponding Ethernet priority / class level. For example, the Pause number
zero applies to priority zero, Pause number one applies to priority one, and so on. This addresses
one shortcoming of the Ethernet Pause mechanism, which is disruptive to all traffic on the link.
However, it still suffers from the other Ethernet Pause limitations.
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.

Enabling an Ethernet PFC

Perform the following steps from Privileged EXEC mode to enable Ethernet PFC.
1. Enter global configuration mode.
switch#configure terminal
2. Specify the 10-gigabit Ethernet interface.
Example of selecting the 10-Gigabit Ethernet interface port 0/2.
switch(config)#interface tengigabitethernet 0/2
3. Enable an Ethernet PFC on the interface.
switch(conf-if-te-0/2)#qos flowcontrol pfc 3 tx on rx on
Example of enabling an interface 802.3x Pause flow control TX and RX.
switch:admin>cmsh
switch>enable
switch#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
switch(config)#interface tengigabitethernet 0/2
switch(conf-if-te-0/2)#qos flowcontrol pfc 3 tx on rx on
switch(conf-if-te-0/2)#exit
switch(config)#end
4. Enter the copy command to save the running-config file to the startup-config file.
switch#copy running-config startup-config
Multicast rate limiting
Multicast rate limiting provides a mechanism to control multicast frame replication and cap the
effect of multicast traffic.