Information Technology Reference
In-Depth Information
A router can use many sources of information to build its RIB. In an internetworked envi-
ronment such as the Internet, routing information is exchanged via a variety of dynamic
routing protocols, which can be Interior Gateway Protocols (IGPs) or Exterior Gateway
Protocols (EGPs). Timely distribution of correct routing information throughout the net-
work is a major component in building a reliable network. Later chapters examine various
techniques to optimize BGP routing architectures for convergence, policy control, and
scalability.
Within the forwarding plane are two major functions: packet classification and packet
forwarding.
Packet classification
is the process of condensing the RIB into a forwarding
information base (FIB). A typical FIB is organized around destination prefixes, with each
prefix associated with a next-hop address, outgoing interface, and so on. Actual
packet
forwarding
is performed by the switching component of the forwarding plane. Specifically,
the router uses the prefix as the key to perform a lookup operation to produce the next-hop
address, outgoing interface, and Layer 2 header, which depends on the type of outgoing
interface.
BGP Processes and Memory Use
Cisco IOS software has three main BGP processes:
•
I/O
•
Router
•
Scanner
Figure 2-1 shows the three BGP processes and the interactions among all the major BGP
components in IOS.
Figure 2-1
BGP Processes in IOS
BGP
Router
BGP I/O
CLI
IP RIB
BGP RIB
BGP
Scanner
TCP
The BGP I/O process handles reading, writing, and executing BGP messages. It provides
the interface between TCP and BGP. On one hand, it reads messages from the TCP socket
and puts them into the BGP input queue (InQ) to be processed by the BGP Router process.
