Which TWO statements about active routes in the Junos routing table are correct?
Trap 1: All routes in the routing table are active.
This is false because Junos keeps routes from multiple sources (e.g., OSPF, IS-IS, static, BGP) in the routing table, and each routing instance's table can contain several routes for the same prefix while only the route with the best route preference is marked active. The remaining routes are retained as inactive, so the routing table always contains a mix of active and inactive routes. Only the active route is considered for forwarding, which is why this statement is incorrect.
Trap 2: Multiple active routes can exist for the same prefix.
By default, Junos installs only one active route per prefix in a routing table, chosen by the lowest route preference and then, if necessary, by tie-breakers such as the origin protocol's internal metrics. Even when equal-cost multipath (ECMP) is configured, the active route is a single route object that carries multiple equal-cost next hops, rather than multiple separate active routes. Therefore, the statement is false as a general rule, and the ECMP exception still does not create multiple active routes for the same prefix.
Trap 3: An active route is always preferred over a passive route.
Junos does not define 'passive routes' as a routing-table state, so the claim is not meaningful in the context of Junos. The routing table categories are active (selected as the best) and inactive (non-best routes held from other protocols), and route preference is a numeric value assigned to protocols, not a comparison between an active and a 'passive' candidate. An inactive route with a higher preference value can become active if the current active route is withdrawn, but there is never a case where both an active and a passive route compete for the same prefix because 'passive' refers to a different feature, such as passive OSPF interfaces.
- A
All routes in the routing table are active.
Why it fails: This is false because Junos keeps routes from multiple sources (e.g., OSPF, IS-IS, static, BGP) in the routing table, and each routing instance's table can contain several routes for the same prefix while only the route with the best route preference is marked active. The remaining routes are retained as inactive, so the routing table always contains a mix of active and inactive routes. Only the active route is considered for forwarding, which is why this statement is incorrect.
- B
Multiple active routes can exist for the same prefix.
Why it fails: By default, Junos installs only one active route per prefix in a routing table, chosen by the lowest route preference and then, if necessary, by tie-breakers such as the origin protocol's internal metrics. Even when equal-cost multipath (ECMP) is configured, the active route is a single route object that carries multiple equal-cost next hops, rather than multiple separate active routes. Therefore, the statement is false as a general rule, and the ECMP exception still does not create multiple active routes for the same prefix.
- C
An active route is installed in the forwarding table.
This correctly describes the forwarding behavior: once a route is selected as active, Junos copies it from the routing table (e.g., inet.0) into the forwarding table that is used by the Packet Forwarding Engine to make forwarding decisions. Active routes are the only routes that are programmed into the PFE, either in hardware or in a kernel forwarding table, depending on the platform. The presence of a route in the forwarding table is the defining characteristic of an active route from a data-plane perspective.
- D
An active route must have a valid next hop.
An active route requires a valid, resolvable next hop because the route cannot be used for forwarding if the next hop is unreachable or unresolved. For example, a static route with a next hop that lacks a matching ARP entry for a directly connected network, or a route whose recursive next-hop resolution fails, will be held in a hidden or inactive state rather than becoming active. Valid next hops include a directly connected interface address, an interface with an associated next-hop address, or an indirect next hop that recursively resolves to a usable path.
- E
An active route is always preferred over a passive route.
Why it fails: Junos does not define 'passive routes' as a routing-table state, so the claim is not meaningful in the context of Junos. The routing table categories are active (selected as the best) and inactive (non-best routes held from other protocols), and route preference is a numeric value assigned to protocols, not a comparison between an active and a 'passive' candidate. An inactive route with a higher preference value can become active if the current active route is withdrawn, but there is never a case where both an active and a passive route compete for the same prefix because 'passive' refers to a different feature, such as passive OSPF interfaces.