3.6.d Implement and troubleshoot network types area types and router types

this is a nice run around… best bet here is that type 4 lsa’s are filtered, or not allowed into stub areas… the ccie quick refererence guide v4.0 however implies that they are… i like to think of type 4 as simply a pointer to the asbr, like it or not that’s how i keep that friggin one straight… and as such, we know the asbr provides redistribution or external routes, type 5’s… since a stub area cannot possibly have type 5’s then it makes sense that the type 4’s are also excluded… however…

pg66 ccie quick reference guide 4.0

Stub area: A stub area is an area that does not permit the advertisement of type 5 (external) LSAs. Instead, these LSAs are replaced with a default route advertisement. Type 3 and 4 advertisements are sent into the area from the ABR. Stub areas are used when all traffic destined to an external network would travel through an ABR. A default route accomplishes this while saving resources.

i hate when that happens…

our man with the plan ivan p. refutes this below…

http://blog.ioshints.info/

To make it more explicit: the type-4 LSA is the glue that ties together a type-5 LSA originated by an out-of-area ASBR with the ABR flooding type-5 into the area. If there are no type-5 LSAs, type-4 LSAs are not needed (you will also not see them for ASBRs in the same area).

i gotta go with ivan here…

note the graphic below implying type 4’s allowed in the stub area, notwithstanding accept is misspelled…

stub_graphic