You are presented with requirements to design a development, testing and production environments. These environment should communicate with each other, yet they should be kept as separate failure…

Question

Options

• AOSPF
• BEIGRP
• CIS-IS
• DBGP

• A
  2% (1)
• B
  12% (6)
• C
  6% (3)
• D
  81% (42)

Explanation

BGP (D) is correct because it is an Exterior Gateway Protocol (EGP) specifically designed to route between separate autonomous systems (AS) - making it ideal when environments must communicate yet remain isolated failure domains. Each environment (dev, test, prod) can be assigned its own AS number, providing logical separation and independent failure boundaries while still exchanging routes. BGP's rich policy controls also let you restrict what routes each environment advertises, enforcing the separation requirement.

Why the distractors are wrong:

• OSPF (A) and IS-IS (C) are Interior Gateway Protocols (IGPs) - they operate within a single domain and share a common topology database, meaning a failure or misconfiguration propagates across all routers in the same area, violating the separate failure domain requirement.
• EIGRP (B) is also an IGP (and Cisco-proprietary) - same problem: it's built for routing inside one administrative domain, not between isolated ones.

Memory tip: Think of BGP as the "Between" protocol - it's what connects separate domains on the internet. Whenever an exam question pairs "separate failure domains" with "must still communicate," that's the BGP signal. IGPs (OSPF, EIGRP, IS-IS) keep things together; BGP keeps things apart while letting them talk.

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