JN0-102 · Question #309
Given the configuration and routing table shown in the exhibit, which routes will be advertised to OSPF neighbors because of the demo policy? destinations, 9 routes (9 active, 0 holddown, 0 hidden) +
The correct answer is B. 192.168.0.0/17 only. Assuming an OSPF export policy is configured to advertise aggregate routes, specifically matching 192.168.0.0/17 or longer prefixes, only the 192.168.0.0/17 aggregate route will be advertised as it is active and has a valid next-hop.
Question
Given the configuration and routing table shown in the exhibit, which routes will be advertised to OSPF neighbors because of the demo policy? destinations, 9 routes (9 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 10.10.10.91/32 *[Direct/0] 00:09:40 > via lo0.0 10.10.10.92/32 *[OSPF/10] 00:01:50, metric 1 > to 172.16.1.2 via ge-0/0/2.0 100.100.1.0/24 *[Static/5] 00:01:50 Reject 172.16.1.0/24 *[Direct/0] 00:06:09 > via ge-0/0/2.0 172.16.1.1/32 *[Local/0] 00:06:09 Local via ge-0/0/2.0 192.168.0.0/16 *[Aggregate/130] 00:00:06 Reject 192.168.0.0/17 *[Aggregate/130] 00:00:06 > to 172.16.1.2 via ge-0/0/2.0 192.168.50.0/24 *[Static/5] 00:00:06 > to 172.16.1.2 via ge-0/0/2.0 192.168.51.0/24 *[Static/5] 00:00:06 > to 172.16.1.2 via ge-0/0/2.0 user@router> show configuration policy-options policy-statement demo { term 1 { from { protocol aggregate; route-filter 192.168.0.0/16 longer; } then accept; } } user@router> show configuration protocols ospf export demo; area 0.0.0.0 { interface ge-0/0/2.0; }
Options
- A192.168.0.0/16 only
- B192.168.0.0/17 only
- C192.168.0.0/16 and 192.168.0.0/17
- D192.168.0.0/17, 192.168.50.0/24, and 192.168.51.0/24
How the community answered
(59 responses)- A10% (6)
- B63% (37)
- C5% (3)
- D22% (13)
Why each option
Assuming an OSPF export policy is configured to advertise aggregate routes, specifically matching `192.168.0.0/17` or longer prefixes, only the `192.168.0.0/17` aggregate route will be advertised as it is active and has a valid next-hop.
The `192.168.0.0/16` route has a 'Reject' next-hop, which means it is a blackhole route and is typically not advertised to neighbors for forwarding unless specifically designed for that purpose, even if it is an aggregate route.
The `192.168.0.0/17` route is an active aggregate route with a valid next-hop. If the `demo` policy is configured to export aggregate routes matching `192.168.0.0/17 orlonger` (implicitly including the prefix itself), this route would be advertised to OSPF neighbors. The `/16` aggregate route has a reject next-hop, making it typically unsuitable for advertising as a forwarding route unless specifically intended.
While `192.168.0.0/17` would be advertised, `192.168.0.0/16` would not due to its 'Reject' next-hop.
The `192.168.50.0/24` and `192.168.51.0/24` routes are static, not aggregate, so they would not match a policy exporting only aggregate routes.
Concept tested: OSPF export policy with aggregate routes
Source: https://www.juniper.net/documentation/us/en/software/junos/routing-policy/topics/topic-map-routing-policy-overview.html
Topics
Community Discussion
No community discussion yet for this question.