Area types control which LSAs are allowed, to shrink tables and speed convergence. All routers in an area must agree.
| Area | LSAs allowed | External | ASBR inside | CLI |
|---|---|---|---|---|
| Normal | 1,2,3,4,5 | yes | yes | default |
| Stub | 1,2,3 | no (5 blocked) + default from ABR | no | area X stub |
| Totally stub (Cisco) | 1,2 | no, only default | no | area X stub no-summary |
| NSSA | 1,2,3,7 | local ASBR via type 7 | yes | area X nssa |
| Totally NSSA (Cisco) | 1,2,7 | 7 + default | yes | area X nssa no-summary |
One-liners: stub = no type 5, NSSA = type 7 inside / 5 outside, totally stub = default only. NSSA ≠ stub because the ASBR is allowed.
Where filtering actually works
| Tool | Filters | Touches LSDB? |
|---|---|---|
area X filter-list prefix (ABR) |
type 3 LSAs | yes |
area X range (ABR) |
summarises type 3 | yes |
summary-address + route-map (ASBR) |
external (type 5) | yes |
distribute-list |
local RIB only — the trap | no |