Jaycee's Networking

May 31, 2009

BGP Processes and Memory Use

Filed under: BGP, IOS — Tags: — Jaycee @ 6:06 pm

A. Example of “BGP Process and Memory Use”:

R1# show processes memory | begin BGP
 PID TTY  Allocated      Freed    Holding    Getbufs    Retbufs Process
  73   0  678981156   89816736   70811036          0          0 BGP Router
  74   0    2968320  419750112      61388    1327064        832 BGP I/O
  75   0          0    8270540       9824          0          0 BGP Scanner
                                 70882248 Total BGP
                                 77465892 Total all processes

1. Allocated column: It shows the total number of bytes allocated since the creation of the process.

2. Freed column: It provides the number of bytes the process has freed since its creation.

3. Holding column: It shows the actual memory that is bing consumed by the process at the moment.

a. BGP Router process accounts for the majority of BGP’s memory use.
b. The memory use for both the BGP I/O and BGP Scanner process are insignificant.

B. BGP Router Process:

1. BGP RIB

a. Includes network entries, path entries, path attributes, and route map and filter list caches.

b. The memory used to store this information can be found in “show ip bgp summary” output.

2. IP RIB for BGP learned prefixes

a. BGP learned prefixes are stored in two types of structures:

(1) NDBs (Network Descriptor Blocks)

(2) RDBs (Routing Descriptor Blocks)

b. Each route in the IP RIB requires one NDB and one RDB per path.

c. If the route is subnetted, additional memory is required to maintain the NDB.

d. The direct memory use for IP RIB can be shown using the “show ip route summary” command.

3. IP switching component for BGP learned prefixes

a. With significatn memory demand is IP switching component, such as FIB structures.

4. BGP Router process requires a small amount of memory for its own operation in addition to what is required to store the routing information, approximately 40KB which is insignificant compared to the overall memory consumed by the BGP router process.

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