Hi, hope the following info will be helpful:
Buffer Tuning
Below is an example from the show buffers command:
Middle buffers, 600 bytes (total 150, permanent 25):
147 in free list (10 min, 150 max allowed)
61351931 hits, 137912 misses, 51605 trims, 51730 created
91652 failures (0 no memory)
In this example, the middle buffers have a lot of failures. This is not a serious problem as it represents only 0.1
% of the hits. These numbers should easily be improved with some buffer tuning.
Depending on the architecture of the router, the buffers you tune generally belong either to I/O memory
(low−end) or main memory (high−end). Before tuning the buffers, first check if you have enough free I/O or
main memory using the first lines of the show memory command.
Here are some general values that you can use:
permanent: take the number of total buffers in a pool and add about 20%. ·
min−free: set min−free to about 20−30% of the permanent number of allocated buffers in the pool. ·
max−free: set max−free to something greater than the sum of permanents and minimums. ·
In the buffer tuning example above, we could enter these commands in the configuration:
buffer middle permanent 180
buffer middle min−free 50
buffer middle max−free 230
Normally, Cisco IOS® software creates buffers dynamically so that these settings should be fine. However, in
case of a traffic burst, the router may not have enough time to create the new buffers, and the number of
failures may continue to increase.
There are two kinds of traffic bursts:
Slow burst: In this case, the router has sufficient time to create new buffers. Increase the number of
min−free buffers. By using free buffers, you can reach the min−free value and then create new
buffers.
·
Fast burst: With fast traffic bursts, the router does not have enough time to create new buffers, so you
should use the free buffers. To do this, modify the number of permanent buffers.
·
Conclusion: If the create counter increases after the initial tuning, increase the min−free (slow burst). If the
failure counter increases, but not the create counter (fast burst), increase the permanent value.
