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ENSLD 1.0 Advanced Addressing and Routing Solutions (25%)

This is the largest-weighted domain on the 300-420 exam, tied with Campus. ENSLD is a design exam, so the questions here are not about typing commands. They give you a business requirement, a topology or a set of constraints, and ask which addressing plan, routing protocol feature or migration strategy fits best, and why the alternatives fail. The protocol mechanics are taught in ENCOR and ENARSI; these pages assume you know them and focus on choices, trade-offs and failure behaviour.

Objective Verb Page
1.1 Structured IPv4 and IPv6 addressing plans Design Addressing Plans
1.2 Stable, secure and scalable routing designs for IS-IS Design IS-IS and EIGRP Design
1.3 Stable, secure and scalable routing designs for EIGRP Design IS-IS and EIGRP Design
1.4 Stable, secure and scalable routing designs for OSPF Design OSPF Design
1.5 Stable, secure and scalable routing designs for BGP (address families, filtering, path preference, route reflectors, load sharing) Design BGP Design
1.6 IPv6 migration strategies (overlay, native, translation) Design IPv6 Migration

How to study this domain

Every page ends with the same pattern you will see on the exam: a scenario with requirements and constraints, then a model answer that names the rejected alternatives. Try to answer the Design exercise on paper before you open the model answer. Most wrong answers on ENSLD are technically valid options that violate one constraint (scale, convergence time, operational skill, security, cost), so train yourself to underline the constraint in every stem.

A useful habit for routing design questions is to ask five things in order:

  1. What is the failure domain? Where should a link flap or a bad update stop?
  2. What is the scale? Number of routers, routes and areas or sites.
  3. What must converge fast, and what may converge slowly?
  4. Who controls the policy? Inside one administration (IGP) or across administrations (BGP)?
  5. What does the operations team already know? A simpler design that the team can run beats an elegant one it cannot.

Time budget: See the study plan.

When you finish, take the Addressing and Routing practice questions. Aim for 80% or better before moving on.