Re: [OSPF] Stub areas and type 4 summary LSAs

[Acee Lindem <[e-mail]>]

Hi Ramakrisha,
You are correct and my implementation does, in fact, generate a SeqNumberMismatch event in this case. 
Thanks,
Acee 
On Sep 20, 2013, at 3:03 AM, RAMAKRISHNADTV wrote:

> Hi,
> 
> Could you please clarify the following point in OSPFv2 (RFC 2328) w.r.t
> stub areas?
> 
> The following is excerpted from Section 10.6 (Receiving Database Description
> Packets):
> 
>        When the router accepts a received Database Description Packet
>        as the next in sequence the packet contents are processed as
>        follows.  For each LSA listed, the LSA's LS type is checked for
>        validity.  If the LS type is unknown (e.g., not one of the LS
>        types 1-5 defined by this specification), or if this is an AS-
>        external-LSA (LS type = 5) and the neighbor is associated with a
>        stub area, generate the neighbor event SeqNumberMismatch and
>        stop processing the packet.  Otherwise, the router looks up the
>        LSA in its database to see whether it also has an instance of
>        ...
> 
> This is correctly saying that stub areas should not process external
> LSAs (LS type 5). But what about type 4 summary LSAs (related to ASBR)?
> As far as I understand, stub areas should not receive these LSAs.
> But this paragraph is not explicit about it. I believe this paragraph
> needs to be updated to indicate that received type 4 summary LSAs and
> type 5 external LSAs should elicit the same behavior in stub areas:
> generate the neighbor event SeqNumberMismatch and stop processing the
> packet.
> 
> On the other hand, originating LSA side description in RFC correctly
> states as follows.
> 
> From Section 12.4.3 (Summary-LSAs):
> 
>                ...If so, a Type 4 summary-LSA is originated for the
>                destination, with Link State ID equal to the AS boundary
>                router's Router ID and metric equal to the routing table
>                entry's cost. Note: these LSAs should not be generated
>                if Area A has been configured as a stub area....
> 
> Regards,
> Ramakrishna DTV.
> 
> 
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