Selecting Route Paths In Bgp - Lenovo Flex System Fabric CN4093 Application Manual

Selecting Route Paths in BGP

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.
4. In the case of equal weight and routes learned from peers that reside in the same
AS, the lower metric is selected.
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 have same route type (eBGP or iBGP), the route with the lower router
ID is selected.
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BGP selects only one path as the best path. It does not rely on metric 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 CN4093 uses the following criteria to select a path when the
same route is received from multiple peers.
AS path weight = 128 x AS path length (number of autonomous systems traversed).
Note: A route with a metric is preferred over a route without a metric.
When the path is selected, BGP puts the selected path in its routing table and
propagates the path to its neighbors.
Chapter 29: Border Gateway Protocol
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