Motorola BSR 2000, Руководство по настройке и управлению

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Release 1.0 Configuring BGP
526360-001-00 Rev. B MGBI 12-3
BGP uses AS path information to prevent routing loops. In BGP, each AS delineates
the route in the path. This enables routers to look for loops by examining the
information sent to them about the path.
Figure 12-1 shows how BGP advertises
routes to neighbors in an AS path.
1. Router Boston originates a route to Router New York.
2. Router New York forwards the route to Router Los Angeles, after adding its AS
to the AS path.
3. Router Los Angeles receives the route and ascertains that it comes from another
AS.
4. Router Los Angeles adds its own AS to the AS path and forwards to Router
Miami.
5. Router Miami receives the route and ascertains that it comes from another AS.
6. Router Miami adds its own AS to the AS path and forwards the route to Router
Dallas.
7. Router Dallas receives the route, determines that the route is a loop since its own
AS is contained in the AS path, and discards the route.
Note: Set up your router with BGP if your AS or router is dual or multihomed
(if it has two or more backbone connections, either direct or daisy-chained
thorough another point of presence). Also, use BGP if the BSR provides IP
routing to a downstream site or customer or if you must preserve AS path
information in your network. If your site is single-homed and you do not
provide IP services or AS paths, consider using static routes instead.
Because external routing requirements are relatively simple, static routing is
easier to set up and to maintain, and it requires less overhead.