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From: Acee Lindem (aceeREDBACK.COM)
Date: Fri May 31 2002 - 07:25:23 CDT
> #2 in my opinion is actually more important and yes I believe in
> having at least a 2nd eligible DR router. But in my scenario, if
> there was a 2nd eligible router, there should have been a BDR...
> The problem exists when their isn't a 2nd eligible DR router.
> #1 The Demand Circuit RFC, sorry folks :-), which specifies
> DNA LSAs, does specify the removal of non-originated LSAs.
> However, I have seen instances where the removal of these
> LSAs is never automaticly flushed from its database
> and thus really need to be flushed by the originator..
Well this is a bug.
> Be safe than sorry. Once the system -ID
> has changed then the originator is NOT the same and will
> not "get back to the LSA's originator," (from section 2.4..
> And this was done because also in 2.4..."There are times when MaxAge
> LSAs stay in a router's database for extended intervals: 1) when
> they are stuck in a retransmission queue on a slow link or 2) when
> a router is not properly flushing them from its database, due to
> software bugs. The prolonged existence of these MaxAge LSAs can
> inhibit the flooding of new instances of the LSA. "
> Thus, even though this section explicitly states "MaxAge LSAs", I
> would not rule out DNA LSAs.. So, again it is safer to just attempt
> to prematurely age ALL originated LSAs.. And then wait for some
> time incase of some form of delays in the flooding..
> Lastly, this item really SHOULD HAVE BEEN MOOT if the router
> selected it's router-ID as the highest loopback interface
> or highest IP address. Maybe that's too Cisco like...
An OSPF router has to handle router ID changes no matter
what algorithm is used to select the default router ID. Most
OSPF implementations allow one to explicitly specify and dynamically
change the router-id (in fact, RFC 2328 lists this as a configuration
parameter in appendix C.1).
> Mitchell Erblich
> PS: Been around to long... :-)
> Acee Lindem wrote:
>>I don't completely agree here.
>>>Just two additional notes..
>>>1) If the router originated DNA (do not age LSAs), then
>>>they really need to be flushed.
>>If you reference section 2.3 of RFC 1793, you'll see that these
>>DNA LSAs will be flushed by the first router that detects
>>they are stale.
>>>2) If the router is the DR and their was no BDR configured,
>>>the DRothers lsdb synchronization will be lost during the
>>>time that reconvergence is re-done with the new router's
>>> So, before the DR is taken down, as a precautionary note,
>>>make sure that at least one of the DRothers will be able to take
>>>over the duties of the down router, while the router ID
>>Are you suggesting that one manually reconfigure a DRother router to
>>make be DR eligible? And then reconfigure it to be
>>DR ineligible once the router ID on the DR is changed. This is what
>>would be required since the fact that there is no BDR implies
>>that none of the other routers on the transit network are DR eligible.
>>A better solution might be to design your network so there is
>>always more than one DR eligible router on each transit network. Maybe
>>this is what you are suggesting.
>>> Mitchell Erblich
>>>"Naidu, Venkata" wrote:
>>>>-> 1. if we disable the ospf admin status should we flush out all
>>>>-> lsas generated by this router or it's not needed.
>>>> Apart from what Vishwas pointed out, most of the implementations
>>>> I have seen are not flushing any LSAs in OSPF shutdown/clear.
>>>> Not flushing normal LSAs upon shutdown won't hurt other routers
>>>> much, but flushing TE-LSAs are some times required.
>>>>-> 2. if we change the router Id of a router than what's need to be
>>>> RFC2328 page 47 reads...
>>>> If a router's OSPF Router ID is changed, the router's OSPF
>>>> should be restarted before the new Router ID takes effect. In
>>>> this case the router should flush its self-originated LSAs from
>>>> the routing domain (see Section 14.1) before restarting, or they
>>>> will persist for up to MaxAge minutes.