Step 1: Examine the Local Preference Selection

Action

To examine a route to determine if local preference is the selection criteria for the single, active path, enter the following JUNOS CLI operational mode command:

user@host> show route destination-prefix < detail >

Sample Output

user@R4> show route 100.100.1.0 detail 

inet.0: 20 destinations, 24 routes (20 active, 0 holddown, 0 hidden)

100.100.1.0/24 (2 entries, 1 announced)

        *BGP    Preference: 170/-201

                Source: 10.0.0.2

                Next hop: 10.1.24.1 via so-0/0/3.0, selected

                Protocol next hop: 10.0.0.2 Indirect next hop: 8644000 277

                State: <Active Int Ext>

                Local AS: 65002 Peer AS: 65002

                Age: 2:22:34    Metric: 5       Metric2: 10 

                Task: BGP_65002.10.0.0.2+179

                Announcement bits (3): 0-KRT 3-BGP.0.0.0.0+179 4-Resolve inet.0 

                AS path: 65001 I

                Localpref: 200

                Router ID: 10.0.0.2

         BGP    Preference: 170/-101

                Source: 10.1.45.2

                Next hop: 10.1.45.2 via so-0/0/2.0, selected

                State: <Ext>

                Inactive reason: Local Preference

                Local AS: 65002 Peer AS: 65001

                Age: 2w0d 1:28:31       Metric: 10 

                Task: BGP_65001.10.1.45.2+179

                AS path: 65001 I

                Localpref: 100

                Router ID: 10.0.0.5

What It Means

The sample output shows that R4 received two instances of the 100.100.1.0 route: one from 10.0.0.2 (R2) and one from 10.1.45.2 (R5). R4 selected the path from R2 as its active path, as indicated by the asterisk (*). The selection is based on the local preference value contained in the Localpref field. The path with the highest local preference is preferred. In the example, the path with the higher local preference value is the path from R2, 200.

The reason that the route from R5 is not selected is in the Inactive reason field, in this case, Local Preference.

Note that the two paths are from the same neighboring network: AS 65001.