Step 4: Examine the IGP Cost Selection

Action

To examine a route to determine if EBGP is selected over IBGP as 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@R6> show route 100.100.4.0 detail 

inet.0: 18 destinations, 20 routes (18 active, 0 holddown, 0 hidden)

100.100.4.0/24 (2 entries, 1 announced)

        *BGP    Preference: 170/-101

                Source: 10.0.0.4

                Next hop: 10.1.46.1 via so-0/0/1.0, selected

                Protocol next hop: 10.0.0.4 Indirect next hop: 864c000 276

                State: <Active Int Ext>

                Local AS: 65002 Peer AS: 65002

                Age: 2:16:11    Metric2: 10 

                Task: BGP_65002.10.0.0.4+4120

                Announcement bits (2): 0-KRT 4-Resolve inet.0 

                AS path: 65001 I

                Localpref: 100

                Router ID: 10.0.0.4

         BGP    Preference: 170/-101

                Source: 10.0.0.2

                Next hop: 10.1.46.1 via so-0/0/1.0, selected

                Next hop: 10.1.36.1 via so-0/0/3.0

                Protocol next hop: 10.0.0.2 Indirect next hop: 864c0b0 278

                State: <NotBest Int Ext>

                Inactive reason: IGP metric

                Local AS: 65002 Peer AS: 65002

                Age: 2:16:03    Metric2: 20 

                Task: BGP_65002.10.0.0.2+179

                AS path: 65001 I

                Localpref: 100

                Router ID: 10.0.0.2

What It Means

The sample output shows that R6 received two instances of the 100.100.4.0 route: one from 10.0.0.4 (R4) and one from 10.0.0.2 (R2). R6 selected the path from R4 as its active route, as indicated by the asterisk (*). The selection is based on the IGP metric, displayed in the Metric2 field. The route with the lowest IGP metric is preferred. In the example, the path with the lowest IGP metric value is the path from R4, with an IGP metric value of 10, while the path from R2 has an IGP metric of 20. Note that the two paths are from the same neighboring network: AS 65001.

The reason that the inactive path was not selected is displayed in the Inactive reason field, in this case, IGP metric.