Juniper JN0-650 Exam - Topic 3 Question 8 Discussion

The exhibit shows router1 (AS 65001) connected to router2 (AS 65002) via two parallel physical links. The show bgp summary output indicates that sessions are established with two neighbors: 10.10.10.1 and 10.10.20.1. Currently, for the second neighbor (10.10.20.1), there are 0 active routes despite having 4 accepted routes, which indicates that BGP has selected only one 'best path' via the first neighbor for forwarding.

BGP Best Path Selection: By default, BGP only selects a single best path for any given destination prefix and installs that one path into the forwarding table. In a topology with parallel links to the same AS, this leads to underutilization of available bandwidth.

Multipath Solution (Option B): To enable active routes from both peers and allow for load-balancing (ECMP) across both links, you must enable the multipath feature.

When the multipath statement is configured under the protocols bgp group ext-peers hierarchy, it tells Junos OS to install multiple equal-cost BGP paths into the routing table and subsequent forwarding table.

Since both neighbors belong to the same peer group (ext-peers) and the same AS (65002), configuring multipath at the group level will apply to both sessions, allowing paths from both neighbors to be marked as 'active'.

Incorrect Options:

Option A: 172.16.1.1 is the loopback address of router2. The exhibit shows peering is currently done using physical interface addresses (10.10.10.1 and 10.10.20.1), so this address is irrelevant to the current active sessions.

Option C: Configuring the neighbor address alone without the multipath parameter will not change the best-path selection behavior.

Option D: 10.10.20.2 is the local interface IP of router1, not the neighbor's IP. BGP multipath must be configured to point to remote peer paths.

Configuration Example for Junos OS 24.4: To implement this, apply the following command: set protocols bgp group ext-peers multipath