Nortel Networks 42C4911 Manual de usuario descargar pdf (Pagina 181)

Alteon OS Application Guide

Chapter 11: Border Gateway Protocol

 18142C4911, January 2007

Selecting Route Paths in BGP

BGP selects only one path as the best path. It does not rely on metrics attributes to determine

the best path. When the same network is learned via more than one BGP peer, BGP uses its

policy for selecting the best route to that network. The BGP implementation on the GbE

Switch Module uses the following criteria to select a path when the same route is received

from multiple peers.

1. Local fixed and static routes are preferred over learned routes.

2. With iBGP peers, routes with higher local preference values are selected.

3. In the case of multiple routes of equal preference, the route with lower AS path weight is

selected.

AS path weight = 128 x AS path length (number of autonomous systems transversed).

4. In the case of equal weight and routes learned from peers that reside in the same AS, the

lower metric is selected.

NOTE – A route with a metric is preferred over a route without a metric.

5. The lower cost to the next hop of routes is selected.

6. In the case of equal cost, the eBGP route is preferred over iBGP.

7. If all routes are from eBGP, the route with the lower router ID is selected.

When the path is selected, BGP puts the selected path in its routing table and propagates the

path to its neighbors.

1 2 ... 176 177 178 179 180 181 182 183 184 185 186 ... 259 260

Sin comentarios

Nortel Networks 42C4911 Manual de usuario Pagina 181