Cisco MDS 9000 series Configuration Manual page 38

Configuring FCIP
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 receiving TCP sends back SACK advertisements to the sender. The sender can then retransmit only
the missing data segments. By default, SACK is enabled on Cisco MDS 9000 Family switches.
To configure SACK, follow these steps:
Command
Step 1
switch(config-profile)# no tcp sack-enable
switch(config-profile)# tcp sack-enable
Window Management
The optimal TCP window size is automatically calculated using the maximum bandwidth parameter, the
minimum available bandwidth parameter, and the dynamically measured round-trip time (RTT).
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.
Note Set the maximum bandwidth to match the worst-case bandwidth available on the physical link,
considering other traffic that might be going across this link (for example, other FCIP tunnels, WAN
limitations). Maximum bandwidth should be the total bandwidth minus all other traffic going across that
link.
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
Cisco MDS 9000 Family NX-OS IP Services Configuration Guide
2-14
Chapter 2
Purpose
Disables SACK.
Enables SACK (default).
Purpose
Configures the maximum available
bandwidth at 900 Mbps, the minimum slow
start threshold at 300 Mbps, and the RTT at
10 msec.
Reverts to the factory defaults. The FCIP
defaults are maximum bandwidth at 1 Gbps,
minimum available bandwidth at 500 Mbps,
and RTT at 1 msec.
Configures the maximum available
bandwidth at 2000 Kbps, the minimum
available bandwidth at 2000 Kbps, and the
RTT at 200 msec.
OL-19525-01,Cisco MDS NX-OS Release 4.2(1)
Configuring FCIP