Information Technology Reference
In-Depth Information
Table 2-4
Test Network and Path Combinations
Networks
(in thousands)
7
20
40 0 0100
100
100
100
120
130
Paths (in
thousands)
14
30
70
67
160
100
200
310
400
170
180
For each network/path pair, memory allocation for the BGP RIB, IP RIB, and IP CEF is
collected, together with memory use reported for the BGP router, IP CEF table, and BGP
and IP tables. For the BGP RIB, memory use is reported for BGP networks, BGP paths, and
path attributes. For IP RIB, data is reported for the NDB and RDB. IP CEF memory data
includes both FIB structures and the mtrie used to store BGP networks.
For each component, the memory is plotted against BGP networks or paths, depending on
the correlation. A linear regression is conducted to obtain an estimation model for that
component. The linear model is expressed in the format of
y
=
b
+
a x
where
y
is a type of component memory to be estimated,
x
is either the number of network
entries or path entries,
b
is the line's intercept (the value of
y
when x is 0), or an estimation
deviation in this case, and
a
is the line's slope, indicating how sensitive the memory is to
the changes of prefixes and paths. The result of the regression is the values of
a
and
b
for
each linear model.
The precision of each regression to the actual data is expressed by
R
2
, the
coefficient of
determination
. Mathematically, R
2
is the ratio of the sum of squares because of regression
over the total sum of squares. It is also called the square of the
correlation coefficient
. The
value of R
2
is between 0 and 1, with 0 being the worst or no correlation and 1 being the best
correlation or a perfect fit.
Estimation Formulas
Using the method described in the preceding section, various estimation formulas are
produced. The following section begins with the memory use before BGP is enabled.
Free Memory Before BGP Is Enabled
After booting up but before any routing protocols are configured, the free memory is 99.8
MB out of the 128 MB DRAM on the GRP, as shown in Example 2-15. The memory is
primarily consumed by expanding the IOS image into DRAM. The processes use another
12.3 MB, leaving 87.5 MB free at this point.
