300-320 Question #678: Real Exam Question with Answer & Explanation

The correct answer is A: It does not allow overlapping addresses from different customers.. A Route Distinguisher (RD) has three key characteristics: it ALLOWS overlapping addresses from different customers (B) - this is its primary purpose; it is a 64-bit (8-byte) unique identifier (C); and it is prepended to IPv4 prefixes to form a 96-bit VPNv4 address used in MP-BGP

Question

Which are the main characteristics of a route distinguisher? (Select three.)

Options

AIt does not allow overlapping addresses from different customers.
BIt allows overlapping addresses from different customers.
CIt is a 64-bit unique identifier.
DIt is a 32-bit unique identifier.
EIt is prepended to the IPv4 prefixes.
FIt is a BGP-extended community.

Explanation

A Route Distinguisher (RD) has three key characteristics: it ALLOWS overlapping addresses from different customers (B) - this is its primary purpose; it is a 64-bit (8-byte) unique identifier (C); and it is prepended to IPv4 prefixes to form a 96-bit VPNv4 address used in MP-BGP (E). The stated answer includes A ('does not allow overlapping addresses'), which is technically incorrect - the RD is precisely the mechanism that ENABLES overlapping customer address spaces to coexist. Choice D is wrong because RD is 64-bit, not 32-bit. Choice F is incorrect because Route Target (RT) is the BGP extended community, not the RD - the RD is part of the VPNv4 NLRI. The correct set of characteristics is B, C, and E.

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