Information Technology Reference
In-Depth Information
Total BGP Memory Use
The total memory use for the BGP Router process is the sum of memory used for all the
components. Using the equations just described, you can estimate the memory use for
each component. By adding the memory use for all six components, you can obtain the
total memory use estimate.
For example, assume that the BGP RIB has 103,213 network entries and 561,072 path
entries. Table 2-5 shows the estimated memory use for each component. The total memory
use for the BGP router is the sum of all the memory use estimates—81.5 MB.
Table 2-5
Memory Use Estimate Example
Path
Attributes
Networks
Paths
IP NDB
IP RDB
IP CEF
Total
Memory Use (MB)
12.1
24.5
3.6
17.8
7.8
15.7
81.5
Table 2-6 summarizes all the slopes.
Table 2-6
Slopes for the Regression Lines
Memory Models
Slope
Networks
114.9
Paths
44.0
Path attributes
6.1
IP NDB
172.5
IP RDB
76.1
IP CEF
151.9
Analysis
Cisco IOS software keeps track of three structures related to BGP: the BGP RIB, the IP
RIB, and the IP CEF. The BGP RIB is used to store prefixes received via BGP in addition
to their associated attributes, which include communities, AS_PATH, and so on. A BGP
speaker may have multiple BGP sessions with an assortment of iBGP and eBGP peers,
resulting in the potential for multiple paths per prefix. Each unique prefix is stored in the
BGP network table, and all the paths for the same prefix are stored as BGP path entries. The
amount of memory that each prefix (or network) and path entry consumes may vary from
release to release.
The
show ip bgp summary
output provides memory use for certain BGP components.
With Cisco IOS software Release 12.0(15)S1, each unique prefix uses 129 bytes, and each
additional path consumes another 36 bytes. For example, if the BGP RIB has 100 prefixes
and 200 paths, the total memory for these entries is (100 * 129) + (100 * 36) = 16,500 bytes.
