
Tune the SRB Network
BC-140
Bridging and IBM Networking Configuration Guide
Enable or Disable the Source-Route Fast-Switching Cache
Rather than processing packets at the process level, the fast-switching feature enables the Cisco IOS
software to process packets at the interrupt level. Each packet is transferred from the input interface
to the output interface without copying the entire packet to main system memory. Fast switching
allows for faster implementations of local SRB between 4/16-MB Token Ring cards in the same
router, or between two routers using the 4/16-Mb Token Ring cards and direct encapsulation.
By default, fast-switching software is enabled when SRB is enabled. To enable or disable
source-route fast-switching, use one of the following commands in interface configuration mode:
Note Using either NetBIOS Byte Offset access filters or access expressions that combine access
filters disables the fast switching of source-route bridging frames.
Enable or Disable the Source-Route Autonomous-Switching Cache
Autonomous switching is a feature that enables the Cisco IOS software to transmit packets from the
input ciscoBus card to the output ciscoBus card without any involvement on the part of the router
processor.
Autonomous switching is available for local SRB between ciscoBus Token Ring (CTR) cards in the
same router. Autonomous switching provides higher switching rates than does fast switching
between 4/16-Mb Token Ring cards. Autonomous switching works for both two-port bridges and
multiport bridges that use ciscoBus Token Ring cards.
In a virtual ring that includes both ciscoBus Token Ring and 4/16-Mb Token Ring interfaces, frames
that flow from one CTR interface to another are autonomously switched, and the remainder of the
frames are fast switched. The switching that occurs on the CTR interface takes advantage of the
high-speed ciscoBus controller processor.
To enable or disable source-route autonomous switching, use one of the following commands in
interface configuration mode:
Note Using either NetBIOS Byte Offset access filters or access-expressions that combine access
filters disables the autonomous switching of SRB frames.
Command Purpose
source-bridge route-cache Enable fast-switching.
no source-bridge route-cache Disable fast-switching.
Command Purpose
source-bridge route-cache cbus Enable autonomous switching.
no source-bridge route-cache cbus Disable autonomous switching.
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