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List:       ms-ospf
Subject:    Re: SPF calculation
From:       Shehzad Merchant <smerchant () EXTREMENETWORKS ! COM>
Date:       1998-11-20 23:26:16
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> -----Original Message-----
> From: John T. Moy [SMTP:jmoy@CASC.COM]
> Sent: Friday, November 20, 1998 2:21 PM
> To:   OSPF@DISCUSS.MICROSOFT.COM
> Subject:      Re: SPF calculation
>
> Suresh-
>
> Yes, the lookup of network-LSAs during the routing calculation
> is performed based on Link State ID only. This information
> is buried in a footnote of RFC 2328 (footnote [14], in Section
> 12.2). Probably it should have been made more visible.
>
> By the way, this is the reason for the behavior that Russell
> Sutherland was complaining about on the list a couple of weeks
> back. To ensure that there is only one network-LSA with a given
> Link State ID, the router that becomes DR must flush any other
> network-LSAs having the same Link State ID, regardless of their
> Advertising Router. See Section 13.4 of RFC 2328.
>
> John
>
Depending on the implementation, some care may need to be exercised here. As
part of flusing the stale network LSA, if the router installs the LSA in its
database while waiting for the ACKs from its neighbours, there could
potentially be 2 network LSAs for the same network in the router's database.
Although a transient condition, care should be taken to ensure that if a
routing calculation does occur during this period, the correct LSA is used.


-Shehzad

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