System information

Troubleshooting Serial Line Problems 15-333
Tuning System Buffers
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.
Figure 15-8 show buffers Command Output
In the show buffers output
• total identifies the total number of buffers in the pool, including used and unused buffers.
• permanent identifies the permanent number of allocated buffers in the pool. These buffers are
always in the pool and cannot be trimmed away.
• in free list identifies the number of buffers currently in the pool that are available for use.
• min identifies the minimum number of buffers that the Route Processor (RP) should attempt to
keep in the free list:
— The min parameter is used to anticipate demand for buffers from the pool at any given time.
— If the number of buffers in the free list falls below the min value, the RP attempts to create
more buffers for that pool.
• max allowed identifies the maximum number of buffers allowed in the free list:
— The max allowed parameter prevents a pool from monopolizing buffers that it doesn’t need
anymore, and frees this memory back to the system for further use.
— If the number of buffers in the free list is greater than the max allowed value, the RP should
attempt to trim buffers from the pool.
• hits identifies the number of buffers that have been requested from the pool. The hits counter
provides a mechanism for determining which pool must meet the highest demand for buffers.
Cookie-Monster>show buffers
Buffer elements:
401 in free list (500 max allowed)
87777499 hits, 0 misses, 0 created
Small buffers, 104 bytes (total 120, permanent 120):
114 in free list (20 min, 250 max allowed)
70005538 hits, 6 misses, 2 trims, 2 created
Middle buffers, 600 bytes (total 90, permanent 90):
88 in free list (10 min, 200 max allowed)
25696696 hits, 27 misses, 27 trims, 27 created
Big buffers, 1524 bytes (total 90, permanent 90):
90 in free list (5 min, 300 max allowed)
8214530 hits, 15 misses, 366 trims, 366 created
Large buffers, 5024 bytes (total 5, permanent 5):
5 in free list (0 min, 30 max allowed)
15017 hits, 12 misses, 16354 trims, 16354 created
Huge buffers, 18024 bytes (total 3, permanent 0):
2 in free list (0 min, 4 max allowed)
297582 hits, 17 misses, 30 trims, 33 created
0 failures (0 no memory)
Trims
Created
Failures