Single-area OSPF is a tutorial; multi-area is what real networks run. This lab builds five RouterOS 7 routers across three areas — a backbone, a stub, and a regular area — so you see ABRs, the LSA types that actually matter, and how RouterOS 7's instance/area/interface-template model expresses it. The twin of the Cisco multi-area OSPF lab.
Areas exist to bound flooding and shrink tables. In a single area, every topology change re-floods every router; split the network into areas joined by a backbone (Area 0) and a change in one area barely ripples into the others. The routers straddling two areas are ABRs — they hold a full topology of each area they touch and advertise summaries (not full detail) between them. A stub area goes further: it refuses external routes and lives off a default from its ABR, shrinking its tables to almost nothing.
RouterOS 7 expresses all this with three objects: an instance, one or more areas bound to it, and interface-templates that place interfaces into areas. This lab wires R1 and R4 as ABRs, makes Area 1 a stub, and proves the LSA types by inspection. It's the RouterOS twin of the Cisco multi-area lab; the theory is shared, the config is v7.
01
R1 is the border between Area 1 and the backbone. One instance, two areas, and interface-templates that assign each interface to the right area — that assignment is what makes a router an ABR.
/routing ospf instance add name=v7 router-id=1.1.1.1 /routing ospf area add name=backbone area-id=0.0.0.0 instance=v7 add name=area1 area-id=0.0.0.1 instance=v7 type=stub # stub! # ether1 faces R5 (Area 1); ether2 faces the backbone (Area 0). /routing ospf interface-template add interfaces=ether1 area=area1 cost=10 add interfaces=ether2 area=backbone cost=10 # Holding interfaces in two different areas = this router is an ABR.
OSPF's cardinal rule: non-backbone areas connect to each other only through Area 0. If Area 2 can't reach Area 0 directly, its routes never propagate — and RouterOS won't warn you, you'll just see missing routes. Here R1 and R4 both border the backbone, so it holds together. If a physical layout can't give an area a direct backbone link, you need a virtual-link across a transit area (supported in v7, but a design smell — fix the topology if you can). Confirm Area 0 is contiguous before blaming anything else.
02
R5 lives entirely in the stub Area 1. It gets a default route from its ABR instead of external detail, so its table stays tiny. The stub type must match on every router in the area.
/routing ospf instance add name=v7 router-id=5.5.5.5 /routing ospf area add name=area1 area-id=0.0.0.1 instance=v7 type=stub /routing ospf interface-template add interfaces=ether1 area=area1 cost=10 # R5 learns inter-area (type-3) summaries + a default from R1, but NO # external (type-5) routes — that's the whole point of a stub. [R5] > /ip route print where ospf # note the 0.0.0.0/0 default, few specifics
03
The whole reason to learn areas is what the LSA database shows. Inspect it and you can see intra-area (type-1/2), inter-area summaries (type-3), and the absence of type-5 in the stub.
[R1] > /routing ospf lsa print type=router area=backbone ... # type-1: routers in the area type=network area=backbone ... # type-2: multi-access segments type=summary area=area1 ... # type-3: inter-area, injected by the ABR [R1] > /routing ospf neighbor print # adjacencies Full in both areas [R5] > /routing ospf lsa print where type~"external" # EMPTY in a stub
| Symptom | Where to look |
|---|---|
| Neighbours stuck in Exchange/Loading | MTU mismatch on the link — a classic OSPF killer. Match MTU both ends. |
| Stub area won't form adjacency | Stub flag not set on every router in the area (must match). |
| Area 2 routes missing everywhere | Area 0 not contiguous / an ABR not actually in the backbone. |
| Suboptimal inter-area path | Costs — tune interface-template cost to steer. |
Takeaways
I design multi-area OSPF on MikroTik and Cisco with area boundaries that make sense, proper stub and summary design, and routing tables that stay small as the network grows instead of ballooning with every new site.
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