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Community Member

Default routes in an area

Hi,

How are the default routes configured in one internal router transmitted to other internal router in an area ? Is it by Type 5 LSA ? Then it should be transmitted to all through the AS as Type 5.Correct me if I am wrong.

Thanks,

Vijay

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Re: Default routes in an area

Hi Vijay,

As soon as an OSPF router originates a type-5 LSA that carries the default route it becomes an ASBR, even if it does not originate any other external routes.

If you try this out on a router, you will see that this router will now set the E-bit in its router-LSA (type-1 LSA), signifying that it considers itself to be an ASBR.

Paresh.

6 REPLIES
Purple

Re: Default routes in an area

Hi,

If you inject a default route by means of default-information originate, this will be carried to all non-stub areas in a type-5 LSA.

Paresh.

Community Member

Re: Default routes in an area

Hi,

For a router to generate Type 5 LSAs, it should be an ASBR.But, how come an ordinary router generate a Type 5 LSA to carry default route ? or Only ASBR router can advertise default route? Correct me if I am wrong.

Thanks,

Vijay

Silver

Re: Default routes in an area

Nopes it is not needed for a Router to be ASBR to generate default. An ABR can generate a NSSA Default ROute ( The route will be N1 and N2 not E1 and E2). A totally stub area would have an IA default Route not an external default route which is genrated with default-information originate

Community Member

Re: Default routes in an area

Hi,

I am not talking about default route generated by ABR(as Type 3 LSA for Stubby Area and as Type 7 LSA for NSSA).I am just talking about the default route generated by a normal router inside a noram area.

I got the document:

http://cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801ec9f0.shtml

which says 'Default routes injected into a normal area can be originated by any OSPF router'

Thanks,

Vijay

Purple

Re: Default routes in an area

Hi Vijay,

As soon as an OSPF router originates a type-5 LSA that carries the default route it becomes an ASBR, even if it does not originate any other external routes.

If you try this out on a router, you will see that this router will now set the E-bit in its router-LSA (type-1 LSA), signifying that it considers itself to be an ASBR.

Paresh.

Community Member

Re: Default routes in an area

Hi,

Thanks for your explanation.

Thanks,

Vijay

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