Re: About DR election after ospf graceful restart

[Acee Lindem <[e-mail]>]

Hi Sanjay,

----- Original Message -----
From: "Sanjay BM" <[e-mail]>
To: <[e-mail]>
Sent: Tuesday, June 29, 2004 5:14 PM
Subject: About DR election after ospf graceful restart


> Hi,
>
> I had couple of questions regarding DR election on helpers after a
> OSPF graceful restart.
>
> RFC3623 states the following:
> ---
> When Router Y exits helper mode for X on a given network segment, it
>    reoriginates its LSAs based on the current state of its adjacency to
>    Router X over the segment.  In detail, Y takes the following actions:
>
>       a) Y recalculates the Designated Router for the segment,
>
>       b) Y reoriginates its router-LSA for the segment's OSPF area,
>
>       c) if Y is Designated Router for the segment, it reoriginates the
>          network-LSA for the segment and
>
>       d) if the segment was a virtual link, Y reoriginates its router-
>          LSA for the virtual link's transit area.
> ---
>
> Question 1:
> Should Router Y (helpers) recalculate the DR for the segment even when
> it exits helper mode successfully i.e, when grace LSAs were flushed
> before grace period expiry.

There may be an optimization where in some cases it is unnecessary.
However, the algorithm is such that the existing DR should remain DR.  Also,
unless you have "lots" of neighbors on the subnet, it isn't all that expensive
to run.

>
> Question 2:
> Assume Router X is of higher priority than Router Y and that Router X
> was the BDR before going through a graceful restart. Should Router X
> become the new DR for the segment when Router Y runs the DR election
> after exiting helper mode?

No. Unless other events come into play, whoever was DR prior to X's
restart should remain DR.



>
> Thanx,
> Sanjay