Dell PowerEdge FX2 Dell PowerEdge FN I/O Aggregator Configuration Guide 9.6(0 - Page 29

Configuring Priority-Based Flow Control

Page 29 highlights

• By default, PFC is enabled on an interface with no dot1p priorities configured. You can configure the PFC priorities if the switch negotiates with a remote peer using DCBX. During DCBX negotiation with a remote peer: - DCBx communicates with the remote peer by link layer discovery protocol (LLDP) type, length, value (TLV) to determine current policies, such as PFC support and enhanced transmission selection (ETS) BW allocation. - If the negotiation succeeds and the port is in DCBX Willing mode to receive a peer configuration, PFC parameters from the peer are used to configured PFC priorities on the port. If you enable the link-level flow control mechanism on the interface, DCBX negotiation with a peer is not performed. - If the negotiation fails and PFC is enabled on the port, any user-configured PFC input policies are applied. If no PFC dcb-map has been previously applied, the PFC default setting is used (no priorities configured). If you do not enable PFC on an interface, you can enable the 802.3x linklevel pause function. By default, the link-level pause is disabled, when you disable DCBx and PFC. If no PFC dcb-map has been applied on the interface, the default PFC settings are used. • PFC supports buffering to receive data that continues to arrive on an interface while the remote system reacts to the PFC operation. • PFC uses the DCB MIB IEEE802.1azd2.5 and the PFC MIB IEEE802.1bb-d2.2. If DCBx negotiation is not successful (for example, due to a version or TLV mismatch), DCBx is disabled and you cannot enable PFC or ETS. Configuring Priority-Based Flow Control PFC provides a flow control mechanism based on the 802.1p priorities in converged Ethernet traffic received on an interface and is enabled by default when you enable DCB. As an enhancement to the existing Ethernet pause mechanism, PFC stops traffic transmission for specified priorities (Class of Service (CoS) values) without impacting other priority classes. Different traffic types are assigned to different priority classes. When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the traffic that is to be stopped. Data Center Bridging Exchange protocol (DCBx) provides the link-level exchange of PFC parameters between peer devices. PFC allows network administrators to create zeroloss links for Storage Area Network (SAN) traffic that requires no-drop service, while retaining packetdrop congestion management for Local Area Network (LAN) traffic. To ensure complete no-drop service, apply the same dcb-map on all PFC and ETS enabled interfaces. 1. Create a DCB map to apply priority based flow control or enhanced transmission selection for specified priority groups and priorities. CONFIGURATION mode dcb-map map-name The maximum is 32 alphanumeric characters. 2. Configure the priority group with PGID, bandwidth percentage or strict priority for ETS and PFC mode. DCB-MAP mode priority-group pg_num [bandwidth percentage | strict-priority] pfc [on | off] pg_num range is from 0 to 7. bandwidth percentage range is from 1 to 100. Data Center Bridging (DCB) 29

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28
  • 29
  • 30
  • 31
  • 32
  • 33
  • 34
  • 35
  • 36
  • 37
  • 38
  • 39
  • 40
  • 41
  • 42
  • 43
  • 44
  • 45
  • 46
  • 47
  • 48
  • 49
  • 50
  • 51
  • 52
  • 53
  • 54
  • 55
  • 56
  • 57
  • 58
  • 59
  • 60
  • 61
  • 62
  • 63
  • 64
  • 65
  • 66
  • 67
  • 68
  • 69
  • 70
  • 71
  • 72
  • 73
  • 74
  • 75
  • 76
  • 77
  • 78
  • 79
  • 80
  • 81
  • 82
  • 83
  • 84
  • 85
  • 86
  • 87
  • 88
  • 89
  • 90
  • 91
  • 92
  • 93
  • 94
  • 95
  • 96
  • 97
  • 98
  • 99
  • 100
  • 101
  • 102
  • 103
  • 104
  • 105
  • 106
  • 107
  • 108
  • 109
  • 110
  • 111
  • 112
  • 113
  • 114
  • 115
  • 116
  • 117
  • 118
  • 119
  • 120
  • 121
  • 122
  • 123
  • 124
  • 125
  • 126
  • 127
  • 128
  • 129
  • 130
  • 131
  • 132
  • 133
  • 134
  • 135
  • 136
  • 137
  • 138
  • 139
  • 140
  • 141
  • 142
  • 143
  • 144
  • 145
  • 146
  • 147
  • 148
  • 149
  • 150
  • 151
  • 152
  • 153
  • 154
  • 155
  • 156
  • 157
  • 158
  • 159
  • 160
  • 161
  • 162
  • 163
  • 164
  • 165
  • 166
  • 167
  • 168
  • 169
  • 170
  • 171
  • 172
  • 173
  • 174
  • 175
  • 176
  • 177
  • 178
  • 179
  • 180
  • 181
  • 182
  • 183
  • 184
  • 185
  • 186
  • 187
  • 188
  • 189
  • 190
  • 191
  • 192
  • 193
  • 194
  • 195
  • 196
  • 197
  • 198
  • 199
  • 200
  • 201
  • 202
  • 203
  • 204
  • 205
  • 206
  • 207
  • 208
  • 209
  • 210
  • 211
  • 212
  • 213
  • 214
  • 215
  • 216
  • 217
  • 218
  • 219
  • 220
  • 221
  • 222
  • 223
  • 224
  • 225
  • 226
  • 227
  • 228
  • 229
  • 230
  • 231
  • 232
  • 233
  • 234
  • 235
  • 236
  • 237
  • 238
  • 239
  • 240
  • 241
  • 242
  • 243
  • 244
  • 245
  • 246
  • 247
  • 248
  • 249
  • 250
  • 251
  • 252
  • 253
  • 254
  • 255
  • 256
  • 257
  • 258
  • 259
  • 260
  • 261
  • 262
  • 263
  • 264
  • 265
  • 266
  • 267
  • 268
  • 269
  • 270
  • 271
  • 272
  • 273
  • 274
  • 275
  • 276
  • 277
  • 278
  • 279
  • 280
  • 281
  • 282
  • 283
  • 284
  • 285
  • 286
  • 287
  • 288
  • 289
  • 290
  • 291
  • 292

By default, PFC is enabled on an interface with no dot1p priorities configured. You can configure the
PFC priorities if the switch negotiates with a remote peer using DCBX. During DCBX negotiation with a
remote peer:
DCBx communicates with the remote peer by link layer discovery protocol (LLDP) type, length,
value (TLV) to determine current policies, such as PFC support and enhanced transmission
selection (ETS) BW allocation.
If the negotiation succeeds and the port is in DCBX Willing mode to receive a peer configuration,
PFC parameters from the peer are used to configured PFC priorities on the port. If you enable the
link-level flow control mechanism on the interface, DCBX negotiation with a peer is not
performed.
If the negotiation fails and PFC is enabled on the port, any user-configured PFC input policies are
applied. If no PFC dcb-map has been previously applied, the PFC default setting is used (no
priorities configured). If you do not enable PFC on an interface, you can enable the 802.3x link-
level pause function. By default, the link-level pause is disabled, when you disable DCBx and PFC.
If no PFC dcb-map has been applied on the interface, the default PFC settings are used.
PFC supports buffering to receive data that continues to arrive on an interface while the remote
system reacts to the PFC operation.
PFC uses the DCB MIB IEEE802.1azd2.5 and the PFC MIB IEEE802.1bb-d2.2.
If DCBx negotiation is not successful (for example, due to a version or TLV mismatch), DCBx is disabled
and you cannot enable PFC or ETS.
Configuring Priority-Based Flow Control
PFC provides a flow control mechanism based on the 802.1p priorities in converged Ethernet traffic
received on an interface and is enabled by default when you enable DCB.
As an enhancement to the existing Ethernet pause mechanism, PFC stops traffic transmission for
specified priorities (Class of Service (CoS) values) without impacting other priority classes. Different traffic
types are assigned to different priority classes.
When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of
the traffic that is to be stopped. Data Center Bridging Exchange protocol (DCBx) provides the link-level
exchange of PFC parameters between peer devices. PFC allows network administrators to create zero-
loss links for Storage Area Network (SAN) traffic that requires no-drop service, while retaining packet-
drop congestion management for Local Area Network (LAN) traffic.
To ensure complete no-drop service, apply the same dcb-map on all PFC and ETS enabled interfaces.
1.
Create a DCB map to apply priority based flow control or enhanced transmission selection for
specified priority groups and priorities.
CONFIGURATION mode
dcb-map
map-name
The maximum is 32 alphanumeric characters.
2.
Configure the priority group with PGID, bandwidth percentage or strict priority for ETS and PFC
mode.
DCB-MAP mode
priority-group
pg_num
[bandwidth
percentage
| strict-priority] pfc [on |
off]
pg_num
range is from 0 to 7.
bandwidth
percentage
range is from 1 to 100.
Data Center Bridging (DCB)
29