Information Technology Reference
In-Depth Information
BGP Processes and Memory Use
Example 2-2
router#show process memory
|
include BGP
PID TTY Allocated Freed Holding Getbufs Retbufs Process
99 0 171331064 28799944 34023220 0 0 BGP Router
100 0 131064 22748136 6796 0 0 BGP I/O
101 0 0 6814116 6796 0 0 BGP Scanner
As indicated in the example, the BGP Router process accounts for the majority of BGP's
memory use (the Holding column). The memory use for both the BGP I/O and BGP Scan-
ner processes are insignificant. Three major components in the BGP Router process
account for the bulk of its memory use:
•
BGP RIB
•
IP RIB for BGP learned prefixes
•
IP switching component for BGP learned prefixes
The information held in the BGP RIB includes network entries, path entries, path attributes,
and route map and filter list caches. The memory used to store this information can be found
in the
show ip bgp summary
output.
BGP learned prefixes in the IP RIB are stored in two types of structures:
•
Network Descriptor Blocks (NDBs)
•
Routing Descriptor Blocks (RDBs)
Each route in the IP RIB requires one NDB and one RDB per path. If the route is subnetted,
additional memory is required to maintain the NDB. The direct memory use for IP RIB can
be shown using the
show ip route summary
command.
The third major element of the BGP Router process with significant memory demand is the
IP switching component, such as FIB structures. Switching paths are discussed later in this
chapter.
The BGP Router process also requires a small amount of memory for its own operation in
addition to what is required to store the routing information; however, the amount of mem-
ory for the process alone is approximately 40 KB and therefore is insignificant compared
to the overall memory consumed by the BGP router process. The case study near the end
of this chapter provides a detailed examination of these components' memory use.
BGP Path Attributes
BGP path attributes are a set of parameters describing the characteristics of a BGP prefix.
Because BGP is foremost a routing policy tool, BGP makes extensive use of these attributes
in influencing the path selection. Effective use of these attributes is critical in designing an
