Chapter 21
| Data Center Bridging Commands
Congestion Notification Commands
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The QCN algorithm is composed of the following two parts:
1. Congestion Point (CP) Algorithm: This is the mechanism by which a congested
bridge or end station buffer samples outgoing frames and generates a
feedback message (CNM – Congestion Notification Message) addressed to the
source of the sampled frame. The feedback message contains information
about the extent of congestion at the CP.
2. Reaction Point (RP) Algorithm: This is the mechanism by which a Rate Limiter
associated with a source decreases its sending rate based on feedback received
from the CP, and increases its rate unilaterally (without further feedback) to
recover lost bandwidth and probe for extra available bandwidth.
Table 112: CN Commands
Command Function Mode
cn Enables congestion notification GC
cn cnm-transmit-priority Configures the dot1p priority used for transmitting
any Congestion Notification Message (CNM)
GC
cn cnpv Sets a dot1p priority to be a Congestion Notification
Priority Value (CNPV)
GC
cn cnpv alternate-
priority
Configures the alternate priority used to remark a
received frame when its dot1p priority is equal to
the CNPV when the defense mode is other than auto
GC
cn cnpv defense-mode Configures the defense mode for a CNPV,
determining whether CN is enabled or not, and if
enabled, whether the port remarks the CNPV to a
non-CNPV value on input, and whether the port
removes CN-tags on output
GC
cn cnpv alternate-
priority
Configures the alternate priority used to remark a
received frame when its dot1p priority is equal to
the CNPV when the defense mode is other than auto
IC
cn cnpv defense-mode Configures the defense mode for a CNPV,
determining whether CN is enabled or not, and if
enabled, whether the port remarks the CNPV to a
non-CNPV value on input, and whether the port
removes CN-tags on output
IC
show cn Shows the global CN status PE
show cn cnpv Shows CNPV information, including defense mode
and alternate priority
PE
show cn cp Shows functional settings and status for the
specified CP
PE
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