Multihoming; Bgp Neighbors - HP 7102dl - ProCurve Secure Router Configuration Manual

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring BGP
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The ISP edge router connecting to the local site forms an MPLS Label Switch
Path (LSP) with the ISP edge router connecting to the authorized remote site.
(An LSP resembles a dynamic PVC.) The edge routers mark packets with an
MPLS label that directs them toward the other router through the LSP so that
only Customer A sites receive Customer A routes.

Multihoming

BGP is particularly useful when your router has more than one connection to
the Internet. These connections can be to the same provider or to two different
providers.
When you have only one Internet connection, static or RIP routing is some-
times a better choice. The lower overhead and simpler configuration outweigh
the loss in control. It does not matter that the router cannot balance loads
because all external traffic has the same destination.
However, in a network with two Internet connections, the router must decide
which connection to use for certain traffic. BGP allows a router to receive
different routes from the various ISPs to which it connects; it can then route
traffic accordingly. BGP also allows a router to advertise different networks
to different neighbors. BGP keeps one link from being overused while leaving
the other idle. This ensures that your organization actually receives the benefit
of the connections for which it has paid.

BGP Neighbors

BGP routers advertise routes to their neighbors. Unlike other routing proto-
cols, BGP does not automatically select a neighbor. You must manually
configure the neighbors with which your private router can communicate.
External neighbors are on the same subnet, but internal neighbors can be on
different subnets. In other words, the ISP router (an external neighbor) is
connected to your router on the same subnet, while a router that is part of
your organization (an internal neighbor) may be on a different subnet at the
local or remote site.
You can use BGP in a WAN to distribute routes to an ISP or to a remote site
through the Internet. The BGP router at each remote site is an internal BGP
neighbor. The local router advertises routes to these neighbors through an
external neighbor such as an ISP router. The external neighbor is the neighbor
you configure on the router.