Migrating from IGRP to EIGRP without redistribution: Your network runs IGRP in autonomous system (AS) 10. You want to introduce EIGRP gradually without configuring redistribution. Which single command enables an easy migration path?

Introduction / Context:
EIGRP is backward compatible with IGRP when the same autonomous system (AS) number is used. This allows smooth coexistence and automatic exchange of routes during migration, avoiding immediate manual redistribution.

Given Data / Assumptions:

• Existing IGRP AS: 10.
• Goal: begin running EIGRP while minimizing configuration complexity.
• Desire: avoid explicit redistribution at first.

Concept / Approach:

By enabling EIGRP with the identical AS number (10), the router engages in automatic route exchange/compatibility features between EIGRP and IGRP. This eases phased migration: neighbors still using IGRP can interoperate while EIGRP is introduced and later fully replaces IGRP.

Step-by-Step Solution:

Verification / Alternative check:

Use show ip protocols and show ip route to verify learned routes and their codes; watch for EIGRP codes (D) appearing alongside or replacing IGRP codes (I).

Why Other Options Are Wrong:

Using a different AS (A) breaks the compatibility shortcut; you would need redistribution.

(C) explicitly configures redistribution, which the question aims to avoid.

(D) is not a valid IOS command.

Common Pitfalls:

Forgetting to disable IGRP after full migration; neglecting no auto-summary if discontiguous networks exist; mixing AS numbers unintentionally.

Final Answer:

router eigrp 10