OSPF LSID with vary length masks

[Acee Lindem <acee at CISCO.COM>]

Hi Zhao-Yang,
Added subject. See inline.

Zhao-Yang Dong wrote:

> In an OSPF link state database, each LSA is supposed to have a unique Link
> State ID (LSID). Sometimes this is not true, especially in multiple vendor
> devices environment. 
>
>
>
> When originating summary and/or AS-external LSAs, how to assign unique LSID
> for a network number who has multiple (different length of) masks is
> described in RFC 2328 appendix E. However, I did not see any discussion in
> RFC 2328 nor this archive how to handle/process summary and/or AS-external
> LSAs received from other routers with the same LSID but different length of
> masks. 
>
>
>
> According RFC 2328, a LSA is identified by LS type, LSID and advertising
> router. To determine which LSA of two LSA instances is newer, LS sequence
> number, checksum and age are compared. Network mask does not seem play any
> role while processing the received LSAs. 
>
>
>
> My question is, for example, if I received a LSA with LSID=A.B.C.D and 24
> bits mask and installed in my database, and later I received the same LSA
> (i.e. same LS type, LSID and advertising router) but with 28 bits mask. If
> the second LSA has the larger sequence number, should I replace my database
> copy with the second LSA?
>  
Yes. As you noted above the LSA payload is not used to determine which 
LSA is newer  (other
than it's contribution to the LSA checksum). Of course, you will need to 
run an incremental (or partial
depending on your terminology) for both the new LSA and the prefix 
corresponding to the old
LSA with the different mask.

Hope this helps,
Acee

> Thanks,
>
> Zhaoyang 
>
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>
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>