Subject: Re: Router Disable and Router Id Cahnge

From: "Naidu, Venkata" <[email-masked]>
Date: Thu, 30 May 2002 09:23:13 -0400

Manish,

-> 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
-> done.

  RFC2328 page 47 reads...

          If a router's OSPF Router ID is changed, the router's OSPF
software
        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.

--
Venkata

---

From: Erblichs <[email-masked]>
Date: Thu, 30 May 2002 15:04:50 -0700

Just two additional notes..

1) If the router originated DNA (do not age LSAs), then
they really need to be flushed.

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
system ID.
        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
is changed.

        Mitchell Erblich
        =====================

---

From: Acee Lindem <[email-masked]>
Date: Thu, 30 May 2002 23:37:57 -0400

Mitchell,

I don't completely agree here.

> 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.

> 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.

--
Acee

---

From: Erblichs <[email-masked]>
Date: Thu, 30 May 2002 22:49:08 -0700

Response...

#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..

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...

Mitchell Erblich
PS: Been around to long... :-)
==================

---

From: Acee Lindem <[email-masked]>
Date: Fri, 31 May 2002 08:25:23 -0400

> and thus really need to be flushed by the originator..

Well this is a bug.

> 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).

--
Acee