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ENCOR 3.2 Layer 3 (part of Infrastructure, 30%)

Infrastructure is the largest ENCOR domain at 30%, and Layer 3 is the heaviest part of it. The verbs are mixed. 3.2.a is compare, so expect side-by-side questions on EIGRP and OSPF behaviour. 3.2.b and 3.2.c are configure and verify, so expect exhibits with show output and lab items where you type OSPF or BGP configuration into a simulated router. 3.2.d is describe, so you need to read a PBR route-map and predict where a packet goes.

You probably run OSPF and BGP every day. The exam still catches experienced engineers on defaults (reference bandwidth, DR election rules, TTL 1 on eBGP, the exact-match rule for network) and on the order of the BGP best-path algorithm. Spend your time there.

Objective Verb Page
3.2.a EIGRP and OSPF: distance vector vs link state, load balancing, path selection, path operations, metrics, area types Compare EIGRP vs OSPF
3.2.b OSPFv2/v3: neighbor adjacency, point-to-point and broadcast network types, DR/BDR, LSA types, passive-interface Configure, verify OSPF Adjacencies, Network Types and LSAs
3.2.b OSPFv2/v3: multiple normal areas, summarization, filtering, OSPFv3 dual stack Configure, verify OSPF Multi-Area, Summarization, Filtering and OSPFv3
3.2.c eBGP between directly connected neighbors: neighbor states, best path, network statement, attributes Configure, verify eBGP
3.2.d Policy-based routing Describe Policy-Based Routing

Time budget: weeks 4 and 5 of the study plan. Week 4 covers 3.2.a and both OSPF pages, ending with the dual-stack OSPF lab. Week 5 covers eBGP and PBR, ending with the eBGP and PBR lab.

Module lab topology

Every page in this module uses the same four IOSv routers so the labs build on each other. See Lab Setup for images and the addressing convention.

graph LR
  R3["R3 area 1<br/>Lo0 10.255.255.3<br/>LANs 10.3.0.0/24 to 10.3.3.0/24"] -- "Gi0/0 10.2.3.0/30" --- R2["R2 ABR<br/>Lo0 10.255.255.2"]
  R2 -- "Gi0/1 10.1.2.0/30 area 0" --- R1["R1 AS 65001<br/>Lo0 10.255.255.1"]
  R1 -- "Gi0/0 203.0.113.0/30 eBGP" --- ISP["ISP AS 65000<br/>Lo0 10.255.255.9"]
Link IPv4 IPv6
R1 Gi0/1 to R2 Gi0/1 (area 0) 10.1.2.0/30, R1 .1, R2 .2 2001:db8:1:2::/64
R2 Gi0/0 to R3 Gi0/0 (area 1) 10.2.3.0/30, R2 .1, R3 .2 2001:db8:2:3::/64
R1 Gi0/0 to ISP Gi0/0 (eBGP) 203.0.113.0/30, R1 .1, ISP .2 2001:db8:1:9::/64
R3 Loopback1 to Loopback4 (area 1 "LANs") 10.3.0.1/24 to 10.3.3.1/24 2001:db8:3:0::/64 to 2001:db8:3:3::/64
Loopback0 on router N 10.255.255.N/32 2001:db8:ffff::N/128
  • Week 4: OSPFv2 and OSPFv3 across area 0 (R1 to R2) and area 1 (R2 to R3), with summarization and filtering on R2.
  • Week 5: eBGP between R1 and ISP, then PBR on R1 steering one subnet to a different next hop.

When you finish, take the Layer 3 practice questions. Aim for 80% or better before moving on.