Information Technology Reference
In-Depth Information
Another use of iBGP is in large corporations where the IGP networks are in smaller inde-
pendent routing domains along organizational or geographic boundaries. In Figure 11-10,
a company has decided to use three independent IGPs: one for the Americas; another for
Asia and Australia; and another for Europe, the Middle East, and Africa. Routes are redis-
tributed into an iBGP core.
Asia
IGP
EMEA
IGP
IBGP Core
America
IGP
Figure 11-10
iBGP in a Large Corporation
Other Uses of iBGP
The CCDA should know at a high level these other uses for
iBGP:
Applying policies in the internal autonomous system with the help of BGP
path attributes:
BGP path attributes are covered in a later section.
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QoS policy propagation on BGP (QPPB):
QPPB uses iBGP to spread common
QoS parameters from one router to other routers in the network. It classifies packets
using IP precedence bits based on BGP community lists, BGP autonomous system
paths, and access lists. After packets are classified, QoS features can enforce policies.
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Multiprotocol BGP peering of Multiprotocol Label Switching (MPLS) virtual
private networks (VPN):
The multiprotocol version of BGP is used to carry MPLS
VPN information between all provider edge (PE) routers within a VPN community.
MP-BGP is defined in RFC 2858. It introduces a new BGP capabilities advertisement
to determine whether a BGP peer supports MP-BGP. It introduces optional nontransi-
tive attributes used to advertise feasible routes to a peer, network layer reachability
information, and other characteristics. It defines an address family identifier (AFI) of
2 to identify IPv6, which is used to convey an IPv4 address as the BGP next hop for
the advertised IPv6 prefixes.
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Route Reflectors
iBGP requires that all routers be configured to establish a logical connection with all other
iBGP routers. The logical connection is a TCP link between all iBGP-speaking routers. The
meshed peers can become very large. Network administrators can use route reflectors to
