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BGP Route Storage and Advertisement, and BGP Routing Information Bases (RIBs)
(Page 2 of 2)
BGP Routing Information Bases (RIBs)
The heart of BGP's system of routing
information management and handling is the database where routes are
stored. This database is collectively called the Routing Information
Base (RIB), but it is in fact not a monolithic entity. It is comprised
of three separate sections that are used by a BGP speaker to handle
the input and output of routing information. Two of these sections themselves
consist of several individual parts, or copies.
The three RIB sections (using the
cryptic names given them by the BGP standards, sorry!) are:
- Adj-RIBs-In: A set of input database
parts that holds information about routes received from peer BGP speakers.
- Loc-RIB: The local RIB. This is
the core database that stores routes that have been selected by this
BGP device and are considered valid to it.
- Adj-RIBs-Out: A set of output database
parts that holds information about routes that this BGP device has selected
to be disseminated to its peers.
Thus, the RIB can be considered either
a single database or a set of related databases, depending on how you
look at it. (The divisions above are conceptual in nature; the entire
RIB can be implemented as a single database with an internal structure
representing the different components, or as separate databases.)
The RIB is a fairly complex data
structure, not just because of this multi-section structure, but because
BGP devices store considerably more information about routes than simpler
routing protocols. Routes are also called paths in BGP, and the
detailed descriptions of them are stored in the form of special BGP
The three sections of the RIB are
the mechanism by which information flow is managed in a BGP speaker.
Data received from Update messages transmitted by peer BGP speakers
is held in the Adj-RIBs-In, with each Adj-RIB-In holding
input from one peer. This data is then analyzed and appropriate portions
of it selected to update the Loc-RIB, which is the main database
of routes this BGP speaker is using. On a regular basis, information
from the Loc-RIB is placed into the Adj-RIBs-Out to be
sent to other peers using Update messages. This information flow
is accomplished as part of the system of route update, selection and
advertisement known as the
BGP Decision Process.
Key Concept: The routine operation of BGP requires BGP speakers to store, update, select and advertise routing information. The central data structure used for this purpose is the BGP Routing Information Base (RIB). The RIB actually consists of three sections: a set of input databases (Adj-RIBs-In) that hold routing information received from peers, a local database (Loc-RIB) that contains the routers current routes, and a set of output databases (Adj-RIBs-Out) used by the router to send its routing information to other routers.
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Version 3.0 - Version Date: September 20, 2005
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