Brocade FastIron Ethernet Switch Traffic Management Guide - Manual (Page 80)

NOTE
Enabling flow control on ports that have auto-neg enabled causes flap because the port pause
capabilities must be advertised and negotiated again with peer.
Ports that have auto-neg disabled do not experience flap.
Configuring priority flow control
Enables PFC globally and for a priority group.
1. Enable priority flow control (PFC)globally.
Device(config)# priority-flow-control enable
2. Enable PFC for priority group (PG) 0.
Device(config)# priority-flow-control 0
Packet buffer management
Packet buffer management.
On Brocade ICX 7750 devices, packet memory can support 960 Gbps bandwidth. The total packet
memory is 12M bytes. ICX 7750 devices run in cut-through mode, which means that cut-through
eligible packets are not buffered. If a packet needs to be buffered, it is buffered after Layer 2 and 3
lookup. Packet priority is classified before buffering.
There are two independent packet admission mechanisms: ingress buffer management and egress
buffer management.
Ingress buffer management
• The ingress buffer mechanism determines whether a packet should be admitted into memory-
based on the state of available memory and the amount of buffer resources in use by the ingress
port priority group.
• It aims to support fair access to buffering resources while also enabling loss-less operation across
a network.
• The memory is logically divided into three sections: guaranteed, shared, and headroom for flow
control in fly packets.
• Ingress buffer limits are automatically configured based on user configuration to support either
loss-less or tail drop operation.
Egress buffer management
• The egress buffer mechanism tracks buffer utilization on a per egress port-priority basis. As these
accounting structures reach the limit, packets that are destined to the congested egress port-
priority are tail-dropped.
• It aims to support fair access to the buffering resources among congested egress ports.
• Any incoming packet is counted only once per egress port regardless of whether it is unicast or
multicast.
• Memory is logically divided into two sections: guaranteed and shared.
• You can configure the qos egress-buffer-profile command to configure a share level, which
determines the maximum number of buffers an egress queue can use as a fraction of the total
Configuring priority flow control
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