Regarding the BGP decision algorithm, which two statements are correct? (Choose two.)

The Border Gateway Protocol (BGP) decision algorithm is a multi-step process used to select the single best path to a destination. A fundamental prerequisite is that the next-hop router for a path must be reachable; if the next-hop is inaccessible (i.e., no route to it exists in the Interior Gateway Protocol), the BGP path is considered invalid and is not eligible for selection. Among the valid paths, the LOCALPREF attribute is one of the first criteria evaluated. This attribute is used within an Autonomous System (AS) to influence the exit point for outbound traffic. A path with a higher LOCALPREF value is always preferred over a path with a lower value.

B. Administrative Distance is used by a router to choose between different routing protocols (e.g., BGP vs. OSPF), not as a step within the BGP path selection algorithm itself.

D. This statement is the opposite of the correct BGP behavior; a higher Local Preference value is preferred, not a lower one.

1. RFC 4271 - A Border Gateway Protocol 4 (BGP-4):

Section 9.1.2.2

Decision Process: "The following rules are used to select a route for a given destination... (c) If the route is learned from an internal peer

and the value of the LOCALPREF attribute is higher for one route than for the others

prefer the route with the higher LOCALPREF." This directly supports answer A.

Section 9.1.2.1

Phase 2: Route Resolution: This section details the process of resolving the BGP NEXTHOP attribute. It states that if the BGP NEXTHOP for a route is not resolvable

the route cannot be installed in the routing table. This supports answer C.

2. MIT OpenCourseWare

6.829 Computer Networks

Fall 2002

Lecture 15: BGP:

Slide 15-21

"BGP Decision Process": The lecture slide lists the BGP decision process steps in order. The first step listed is "1. Highest Local Preference

" confirming that a higher value is preferred. The process implicitly requires a valid

reachable next-hop before these steps are applied.

3. Ericsson IP Operating System

CLI Command Reference:

In documentation for Ericsson routers (such as the Router 6000 series)

the description of the BGP decision process consistently aligns with RFC 4271. The show router bgp routes command output and configuration guides for route-policies confirm that a higher local-preference is preferred and that routes with an unresolved next-hop are marked as invalid and not used. (e.g.

Section: "BGP Route Selection" in relevant configuration guides).