Re: OSPFv3 BadLSReq

[Acee Lindem <[e-mail]>]

Taisuke Sasaki wrote:
> Acee and Sina,
>
> Thank you for your detailed explanation.
> I read a rfc2328 14.1 again and carefully.
>
> Acee said:
>
>>R2 should place the MaxAge LSA on neighbor R1's retransmission list
>>when it flushes it. The LSA should not be removed from R2's
>>link state database as long as there are routers in exchange or
>>loading state. Refer to RFC 2328 section 14.1.
>
>
> Now, I understand that OSPF prevent R1 from BadLSReq event
> from the next 2 important points.  right?

Taisuke,

Almost correct.

>
> R1) The premature aging process guarantees that
>     MaxAge LSA is never flushed from its link state database
>     as long as it is contained on any neighbor LS-Retransmission
>     list.
>     (this is what Acee pointed out)

RFC 2328 states that a MaxAge LSA shouldn't be deleted from the
link state database as long as there are neighbors in Exchange
or Loading state.


>
> R2) Receiving R1's MaxAge LSA makes R2 delete the same instance of
>     the LSA from the LS-Request list associated with R1, if needed.
>     (this is what Sina pointed out)


Yes.

>
>      +---+                +---+
>      |R1 |----------------|R2 |
>      +---+                +---+
>
>
>
>
>>Taisuke
>>
>>-> The point is below:
>>-> 1) R1 told R2 that R1 had an Intra-Area-Prefix-LSA associated
>>->    with a Router-LSA in Database Description packets.
>>->    So, R2 will request the Intra-Area-Prefix-LSA.
>>->
>>-> nevertheless,
>>->
>>-> 2) When R1 receives a LS-Request packet from R2,
>>->    it is possible that R2's neighbor state is already full,
>>
>>I guess you meant to say "R1's neighbor state is already Full"
>>
>>->    and there is no router in exchange or loading state,
>>->    and an Intra-Area-Prefix-LSA associated with a Router-LSA
>>->    is already flushed in R1's link state database.
>>->    So, BadLSReq event will happen.
>>
>>The point that you missed is that when R1 maxage its LSA it is expecting
>>to get an Ack and when R2 receive the Maxage LSA it will remove it from
>>its link state request list ( a part from sending an Ack )
>>
>>--
>>
>>From 2328
>>
>>(b) Else, if the adjacency is not yet full (neighbor state
>>                is Exchange or Loading), examine the Link state request
>>                list associated with this adjacency.  If there is an
>>                instance of the new LSA on the list, it indicates that
>>                the neighboring router has an instance of the LSA
>>                already.  Compare the new LSA to the neighbor's copy:
>>
>>                o   If the new LSA is less recent, then examine the next
>>                    neighbor.
>>
>>                o   If the two copies are the same instance, then delete
>>                    the LSA from the Link state request list, and
>>                    examine the next neighbor.[20]
>>
>>                o   Else, the new LSA is more recent.  Delete the LSA
>>                    from the Link state request list.
>>--
>>
>>
>>Sina
>
>
> ---
> taisuke sasaki
>


--
Acee