Information Technology Reference
In-Depth Information
On older platforms, inverting the transmit clock might require that you move a physical
jumper.
Note
Adjusting Buffers
Excessively high bandwidth utilization greater than 70 percent results in reduced overall performance
and can cause intermittent failures. For example, DECnet file transmissions might be failing because of
packets being dropped somewhere in the network.
If the situation is bad enough, you
must
increase the bandwidth of the link. However, increasing the
bandwidth might not be necessary or immediately practical. One way to resolve marginal serial line
overutilization problems is to control how the router uses data buffers.
In general, do
not
adjust system buffers unless you are working closely with a Cisco
technical support representative. You can severely affect the performance of your hardware
and your network if you incorrectly adjust the system buffers on your router.
Caution
Use one of the following three options to control how buffers are used:
•
Adjust parameters associated with system buffers.
•
Specify the number of packets held in input or output queues (hold queues).
•
Prioritize how traffic is queued for transmission (priority output queuing).
The configuration commands associated with these options are described in the Cisco IOS configuration
guides and command references.
The following section focuses on identifying situations in which these options are likely to apply and
defining how you can use these options to help resolve connectivity and performance problems in
serial/WAN interconnections.
Tuning System Buffers
There are two general buffer types on Cisco routers:
hardware buffers
and
system buffers
. Only the
system buffers are directly configurable by system administrators. The hardware buffers are specifically
used as the receive and transmit buffers associated with each interface and (in the absence of any special
configuration) are dynamically managed by the system software itself.
The system buffers are associated with the main system memory and are allocated to different-size
memory blocks. A useful command for determining the status of your system buffers is the
show buffers
exec command. Figure 15-8 shows the output from the
show buffers
command.
