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Advanced FCIP Profile Configuration
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m .
The configured round-trip-time parameter determines the window scaling factor of the TCP
Note
connection. This parameter is only an approximation. The measured RTT value overrides the round trip
time parameter for window management. If the configured round-trip-time is too small compared to
the measured RTT, then the link may not be fully utilized due to the window scaling factor being too
small.
The min-available-bandwidth parameter and the measured RTT together determine the threshold below
which TCP aggressively maintains a window size sufficient to transmit at minimum available bandwidth.
The max-bandwidth-mbps parameter and the measured RTT together determine the maximum window
size.
To configure window management, follow these steps:
Command
Step 1
switch(config-profile)# tcp max-bandwidth-mbps
900 min-available-bandwidth-mbps 300
round-trip-time-ms 10
switch(config-profile)# no tcp max-bandwidth-mbps
900 min-available-bandwidth-mbps 300
round-trip-time-ms 10
switch(config-profile)# tcp max-bandwidth-kbps
2000 min-available-bandwidth-kbps 2000
round-trip-time-us 200
Monitoring Congestion
By enabling the congestion window monitoring (CWM) parameter, you allow TCP to monitor
congestion after each idle period. The CWM parameter also determines the maximum burst size allowed
after an idle period. By default, this parameter is enabled and the default burst size is 50 KB.
The interaction of bandwidth parameters and CWM and the resulting TCP behavior is outlined below:
•
•
•
The software uses standard TCP rules to increase the window beyond the one required to maintain the
min-available-bandwidth to reach the max-bandwidth.
The default burst size is 50 KB.
Note
Cisco MDS 9000 Family Configuration Guide
33-10
If the average rate of the Fibre Channel traffic over the preceding RTT is less than the
min-available-bandwidth multiplied by the RTT, the entire burst is sent immediately at the
min-available-bandwidth rate, provided no TCP drops occur.
If the average rate of the Fibre Channel traffic is greater than min-available-bandwidth multiplied
by the RTT, but less than max-bandwidth multiplied by the RTT, then if the Fibre Channel traffic is
transmitted in burst sizes smaller than the configured CWM value the entire burst is sent
immediately by FCIP at the max-bandwidth rate.
If the average rate of the Fibre Channel traffic is larger than the min-available-bandwidth multiplied
by the RTT and the burst size is greater than the CWM value, then only a part of the burst is sent
immediately. The remainder is sent with the next RTT.
Chapter 33
Purpose
Configures the maximum available
bandwidth at 900 Mbps, the minimum slow
start threshold at 300 Mbps, and the RTT at
10 ms.
Reverts to the factory defaults. The FCIP
defaults are maximum bandwidth at 1 Gbps,
minimum available bandwidth at 500 Mbps,
and RTT at 1 ms.
Configures the maximum available
bandwidth at 2000 Kbps, the minimum
available bandwidth at 2000 Kbps, and the
RTT at 200 ms.
OL-6973-03, Cisco MDS SAN-OS Release 2.x
Configuring FCIP
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