That would be a good test, actually. I think your summarization of the "feature" is
right on. It's almost as if the router thinks "Well, we're running OSPF so *surely*
he must not *really* want 'no ip classless' turned on. So I'll go ahead and operate
classlessly anyway."
This is definitely pretty odd. I think tonight when I get home I'll rearrange my
setup so that instead of doing this on a 4000 running 11.2(25a), I'll use a 2501
running 12.0(16). Perhaps this really is a feature that was fixed in later releases.
Thanks,
John
>>> "Bob Vance" <[EMAIL PROTECTED]> 3/26/01 9:23:46 AM >>>
Bug? -- or "feature" as you say :)
What was really telling to me was when you added the static default
route on top of the OSPF-installed default. The higher admin distance
made the static route be preferred and the routing process behaved
"normally" ("classfully").
Perhaps the feature is :
Hmmm. I see this OSPF installed route. I guess he *really* wants to
run
classlessly, else he'd be running some older protocol !
But you'd think that the code never even gets to any the supernet of
10.5.0.0.
It would really have to be written in to look for OSPF routes before
behaving classfully.
I wonder what would happen if you advertised 8.0.0.0 (being a "supernet
of 10.0.0.0) from C instead of 0.0.0.0 :) -- to see if it's a general
behavior or specifically looking for 0.0.0.0.
-------------------------------------------------
Tks | <mailto:[EMAIL PROTECTED]>
BV | <mailto:[EMAIL PROTECTED]>
Sr. Technical Consultant, SBM, A Gates/Arrow Co.
Vox 770-623-3430 11455 Lakefield Dr.
Fax 770-623-3429 Duluth, GA 30097-1511
=================================================
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
John Neiberger
Sent: Sunday, March 25, 2001 1:32 PM
To: Vincent
Cc: [EMAIL PROTECTED]
Subject: Re: IP Classless Revisited (More info)
Metric shouldn't have anything to do with it. Whether I'm using RIP or
OSPF
the default route is being added to the routing table of the hub router.
The issue is that with no ip classless configured, the hub router should
NOT
ever pick the default route when trying to reach unknown subnets of the
10.x.x.x network.
In my case, when RIP installed the default route it behaves correctly.
When
OSPF installed the route it behaved as if 'ip classless' were
configured.
Very odd.
John
> I guess in faovour of metric.
>
> "John Neiberger" <[EMAIL PROTECTED]> ���g��l��
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > Okay, I just tried this with RIP advertising the default route and
I'm
> even
> > more confused! Now, it behaves as I would expect. With no ip
classless,
> > pings to unknown 10.x.x.x subnets are unroutable even though there
is a
> > default route in the routing table.
> >
> > With no ip classless, why does my router take the default route
when it
> was
> > installed by OSPF but not when it was installed by RIP? I would
expect
it
> > to never take the default route for 10.x.x.x addresses with no ip
> classless.
> >
> > This really concerns me because I was taking a practice CCIE
written
exam
> a
> > few days ago and ran across a question like this and I answered the
> question
> > assuming normal behavior of no ip classless and got it right. Now
I'm
> > thinking there are some more twists to its behavior that i'm not
aware
of.
> >
> > John
> >
> > > Sure, I'll try that but I don't see why it should matter. As I
> > understand
> > > it, ip classless affects routing table lookups only and it
doesn't
care
> > how
> > > those routes were installed into the table.
> > >
> > > Although, given this behavior, my assumption might be wrong.
> > >
> > > Thanks,
> > > John
> > >
> > > > John,
> > > > Interesting. I think this is due to OSPF, not redistribution
> problem.
> >
> > > Can you try running RIP instead of OSPF ?
> > > >
> > > > Cheers,
> > > > YY
> > > >
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
Behalf
> Of
> > > > John Neiberger
> > > > Sent: Sunday, March 25, 2001 5:28 AM
> > > > To: [EMAIL PROTECTED]
> > > > Subject: IP Classless Revisited (this is just odd...)
> > > >
> > > >
> > > > Ok, just when you thought it was safe to go back in the
water....
Or
> > > should
> > > > I say, just when I thought I understood the behavior of 'ip
> classess'
> > and
> > > > 'no ip classless'.... Let me summarize my lab setup.
> > > >
> > > > RouterA-----RouterB------RouterC
> > > >
> > > > Pretty simple. AtoB is 10.1.1.0/24, BtoA is 10.1.2.0/24.
OSPF
is
> > > running
> > > > on both links. 'ip classless' is on A and C, but not B
initially.
> On
> > B
> > > I
> > > > see these routes:
> > > >
> > > > 10.0.0.0/24 is subnetted, 2 subnets
> > > > C 10.1.2.0 is directly connected, Serial1
> > > > C 10.1.1.0 is directly connected, Serial0
> > > >
> > > > That's what I expect to see. Then I add a default route on
B,
'ip
> > route
> > > > 0.0.0.0 0.0.0.0 10.1.1.2'. With no ip classless configured,
any
> > packets
> > > to
> > > > unknown subnets of 10.0.0.0/8 should be dropped. I tested it
and
> that
> > is
> > > > the case. With 'ip classless' configured, and unknown
packets
> > regardless
> > > of
> > > > major network get routed to 10.1.1.2.
> > > >
> > > > Now here is what I don't understand. Let's turn off ip
classless
on
> B
> > > > again, then go to Router C and add a default route to null0
and
> > > > default-information originate to the ospf process. I now see
this
> in
> > > router
> > > > B:
> > > >
> > > > 10.0.0.0/24 is subnetted, 2 subnets
> > > > C 10.1.2.0 is directly connected, Serial1
> > > > C 10.1.1.0 is directly connected, Serial0
> > > > O*E2 0.0.0.0/0 [110/1] via 10.1.2.2, 00:06:38, Serial1
> > > >
> > > > There is indeed a default route. With no ip classless
configured, I
> > > would
> > > > expect the same behavior as before. If I were to ping
10.5.5.5
the
> > > packets
> > > > should be unroutable, but they're not! They get routed to
the
> default
> > > route
> > > > whether or not ip classless is configured.
> > > >
> > > > Why is a default route learned through a routing protocol
treated
> > > > differently than a manually configured default route? I went
> through
> > > this
> > > > entire process twice and I just don't understand the
behavior.
> > > >
> > > > What am I missing? I know it's going to be something
obvious,
but I
> > > don't
> > > > see it yet.
> > > >
> > > > Ok, I just now tried this: with the ospf external default
route
> still
> > in
> > > > the routing table, I pinged 10.5.5.5 and it took the default
route.
> > Then
> > > I
> > > > manually added a default static route and the destination
became
> > > unroutable
> > > > due to 'no ip classless' being configured. Removing the
static
> > default
> > > it
> > > > becomes routable again.
> > > >
> > > > Weird. What's going on?
> > > >
> > > > Thanks,
> > > > John
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > _______________________________________________________
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