An Nokia 7750 SR receives a route via an IS-IS LSP with internal reach ability, and receives the same route via an OSPF type 5 LSA. If al protocol preferences are default, which route will be installed in the route table?

The Nokia 7750 SR selects the best route to a destination by first comparing the protocol preference values of all available routes. A lower preference value is more preferred. The default preference for an internal IS-IS route is 15 for Level 1 or 18 for Level 2. The default preference for an external OSPF route, learned via a Type 5 LSA, is 150. Since both 15 and 18 are significantly lower than 150, the router will select the IS-IS route as the best path and install it in the routing table.

B. The OSPF route has a default preference of 150, which is higher (less preferred) than the IS-IS route's preference (15 or 18).
C. ECMP (Equal-Cost Multi-Path) is only possible for routes that have the same protocol preference. These routes have different preferences and are not eligible for ECMP.
D. The router installs only the single best path into the routing table. Multiple paths are not installed unless they are equal-cost, which is not the case here.

1. Nokia 7750 SR OS Unicast Routing Protocols Guide, SR OS 22.10.R1, Section: Unicast Routing Overview, Subsection: Route Preference.

This section provides a table of default route preference values. It lists "IS-IS Level 1" with a preference of 15, "IS-IS Level 2" with a preference of 18, and "OSPF External" with a preference of 150. This confirms that an internal IS-IS route is preferred over an external OSPF route. (Document ID: 3HE 18130 AAAC TQZZA 01)

2. Nokia 7750 SR OS Unicast Routing Protocols Guide, SR OS 22.10.R1, Section: OSPF, Subsection: OSPF Areas and Route Types.

This section describes OSPF route types, confirming that Type 5 LSAs represent routes to external destinations. The guide states, "External routes are learned by an ASBR from an external routing protocol (for example, BGP) and are flooded throughout the AS." This clarifies the nature of the OSPF route in the question. (Document ID: 3HE 18130 AAAC TQZZA 01)