Nortel Web OS 10.0, Application Manual

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Web OS 10.0 Application Guide
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Chapter 1: Basic IP Routing
212777-A, February 2002
Border Gateway Protocol (BGP)
Border Gateway Protocol (BGP) is an Internet protocol that enables routers on a network to
share and advertise routing information with each other about the segments of the IP address
space they can access within their network and with routers on external networks. BGP allows
you to decide what is the “best” route for a packet to take from your network to a destination
on another network rather than simply setting a default route from your border router(s) to your
upstream provider(s). BGP is defined in RFC 1771.
Alteon Web switches can advertise their IP interfaces and virtual server IP addresses using
BGP and take BGP feeds from as many as four BGP router peers. This allows more resilience
and flexibility in balancing traffic from the Internet.
Internal Routing Versus External Routing
To ensure effective processing of network traffic, every router on your network needs to know
how to send a packet (directly or indirectly) to any other location/destination in your network.
This is referred to as internal routing and can be done with static routes or using active, inter-
nal routing protocols, such as RIP, RIPv2, and OSPF.
It is also useful to tell routers outside your network (upstream providers or peers) about the
routes you can access in your network. External networks (those outside your own) that are
under the same administrative control are referred to as autonomous systems (AS). Sharing of
routing information between autonomous systems is known as external routing.
External BGP (eBGP) is used to exchange routes between different autonomous systems
whereas internal BGP (iBGP) is used to exchange routes within the same autonomous system.
An iBGP is a type of internal routing protocol you can use to do active routing inside your net-
work. It also carries AS path information, which is important when you are an ISP or doing
BGP transit.
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The iBGP peers must be part of a fully meshed network, as shown in Figure 1-3 .