OSPF — multi-area + the ABR

• Routing
• Intermediate
• 14 min
• 3 steps
• Cisco IOS-style

Open this lab in your browser →

Free · no install · no account

Scenario

OSPF scales by *area*. Each area maintains its own LSDB; flooding stops at the area boundary. ABRs (Area Border Routers) bridge two or more areas and generate Type-3 Summary LSAs that represent intra-area routes from one area in the other area's LSDB. The ABR rule: - At least one interface in area 0 (the backbone). - At least one interface in a non-zero area. - Without an interface in area 0, a router in two non-zero areas is *not* an ABR — its inter-area summaries can't form a consistent topology. In this lab R2 is the ABR. R1 sits in area 1 with a loopback 1.1.1.1/32; R3 sits in area 0. After convergence R3 should see 1.1.1.1/32 via R2 as O IA (ospf-inter), not O (intra-area).

Topology

3 × router · Cisco IOS-style

• R1 — router
• R2 — router
• R3 — router

What you will do

1. On R3, run show ip route. Confirm 1.1.1.1/32 is present and tagged O IA (ospf-inter).

2. From R3, ping R1's loopback at 1.1.1.1. Cross-area connectivity proves the ABR is forwarding.

3. On R2, run show ip ospf border-routers (or show ip ospf looking at the ABR flag) to confirm it's recognised as the area's ABR.

Open this lab in your browser →

More labs on this topic

• Syntax delta — static route (Extreme EXOS)Beginner · 4 min
• Syntax delta — static route (Cisco IOS)Beginner · 4 min
• Syntax delta — static route (Juniper Junos)Beginner · 5 min
• Syntax delta — static route (VyOS)Beginner · 5 min
• Static routes — fix hub-and-spokeBeginner · 12 min
• Static routes — egress-interface form (point-to-point)Beginner · 8 min

This lab in other languages

OSPF — Multi-Area + der ABROSPF — multi-área + el ABROSPF — multi-área + o ABROSPF — multi-zones + l'ABROSPF — multi-area + ABROSPF — 多区域 + ABROSPF — multi-area + l'ABROSPF — マルチエリア + ABROSPF — 멀티 에어리어 + ABROSPF — много областей + ABROSPF — çoklu alan + ABROSPF — đa area + ABR