Selecting Route Paths In Bgp; Equal Cost Multi-Path; Multipath Relax - Lenovo RackSwitch G8264 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
4. In the case of equal weight and routes learned from peers that reside in the same
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

Equal Cost Multi-Path

Multipath Relax

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G8264 Application Guide for ENOS 8.4
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 G8264 uses the following criteria to select a path when the
same route is received from multiple peers.
weight is selected.
AS path weight = 128 x AS path length (number of autonomous systems traversed).
AS, the lower metric is selected.
Note: A route with a metric is preferred over a route without a metric.
ID is selected.
When the path is selected, BGP puts the selected path in its routing table and
propagates the path to its neighbors.
BGP can be configured to load balance the traffic over multiple paths if first six
steps in path selection are identical and the next‐hop of the route differs.
BGP multipath relax functionality allows load balancing across routes with
different autonomous system paths, but equal in length (same as‐path length).
With this option disabled, both autonomous system paths and as‐path length must
be identical for load sharing. This functionality can be enabled using the
command:
RS G8264(config­router­bgp)# bestpath as­path multipath­relax