From: Joseph Saad (joseph.samir.saad@gmail.com)
Date: Wed Oct 24 2007 - 08:56:36 ART
Here we go:
5+4+3+2+1 is correct but not all of them will work due to the need to elect
DR or not. This leaves 9 working combinations only.
Ofcourse timers, neighbor command and underlying support of L2 to broadcast
or not are other governing factor.
broadcast (5)
broadcast
non-broadcast
point-to-point (can't work)
point-to-multipoint (can't work)
point-to-multipoint non-broadcast (can't work)
non-broadcast (4)
non-broadcast
point-to-point (can't work)
point-to-multipoint (can't work)
point-to-multipoint non-broadcast (can't work)
point-to-point (3)
point-to-point
point-to-multipoint
point-to-multipoint non-broadcast
point-to-multipoint (2)
point-to-multipoint
point-to-multipoint non-broadcast
point-to-multipoint non-broadcast (1)
point-to-multipoint non-broadcast
Total number of unqiue combinations are 5+4+3+2+1 = 15. (This is what I
think Scott meant).
Total number of possibly working unique combinations are 2+1+3+2+1 = 9.
Joseph.
On 10/24/07, Tarun Pahuja <pahujat@gmail.com> wrote:
>
> Joseph,
> We had already concluded that no formula could be used to find
> out the possible matches as the requirements could not be put in a
> mathematical equation.
>
> I was only correcting the 5+4+3+2+1 statistical theory proposed in one of
> the previous thread. It should have been n(n-1)/2. We were in Math World;-)
>
> If you carefully read the starting threat, the question posed was how
> many possible combinations are possible with 3 different interface types and
> 5 different ospf network types which can work together. The number would be
> much larger than 15, and as Scott mentioned, that is the part about studying
> ;-)
>
> Thanks,
> Tarun
>
>
>
>
> On 10/24/07, Joseph Saad <joseph.samir.saad@gmail.com> wrote:
> >
> > This formula assumes that the same type can't be used at the 2 ends. i.e.
> > once you pick a type from the basket, it is no longer available for you to
> > match on the other end.
> >
> > Hence, this formula is not correct.
> >
> > 15 is the correct number of different combinations irrespective of
> > timers and irrespective whether a DR needs to be elected.
> >
> > Scott wins ... but whom am I to judge.
> >
> > Cheers,
> > Joseph.
> >
> > On 10/24/07, Tarun Pahuja <pahujat@gmail.com > wrote:
> > >
> > > Slight correction, Math says that if you have 5 possible combinations,
> > > the
> > > possible number of combinations would be n(n-1)/2. Therefore, The
> > > possible
> > > ways would have been 10 and not 15(in which one could try to form
> > > adjacency
> > > ).
> > >
> > > 5X(5-1)/2 = 10
> > >
> > > Thanks,
> > > Tarun Pahuja
> > > CCIE#7707(R&S,Security,SP,Voice,Storage),CCSI
> > >
> > >
> > > On 10/23/07, Scott Morris < smorris@ipexpert.com> wrote:
> > > >
> > > > hehehehe... Yes, the response was a joke. (sort of)
> > > >
> > > > There are indeed 15 ways to combine those network types, math
> > > doesn't
> > > > lie. No, all of them will not work together.
> > > >
> > > > However, that's the point of learning is it not? If you are
> > > interested in
> > > > finding some document which may or may not contain all the
> > > possibilities and
> > > > memorize it, go ahead. If you are interested in trying something
> > > out and
> > > > attempting to learn WHY it will or will not work, you'll have much
> > > better
> > > > retention of knowledge and depth of knowledge at that point.
> > > >
> > > > The second path will take a little longer, but the long-term reward
> > > is
> > > > much greater.
> > > >
> > > > "Any fool can know. The point is to understand." -- Albert Einstein
> > >
> > > >
> > > >
> > > > Scott Morris, *CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
> > > > JNCIE-M #153**, JNCIS-ER, CISSP, et al.*
> > > > *CCSI/JNCI-M/JNCI-ER*
> > > > VP - Technical Training - IPexpert, Inc.
> > > > IPexpert Sr. Technical Instructor
> > > >
> > > > A Cisco Learning Partner - We Accept Learning Credits!
> > > >
> > > > smorris@ipexpert.com
> > > >
> > > > Telephone: +1.810.326.1444
> > > > Fax: +1.810.454.0130
> > > > http://www.ipexpert.com
> > > > ------------------------------
> > > > *From:* Tarun Pahuja [mailto: pahujat@gmail.com]
> > > > *Sent:* Tuesday, October 23, 2007 4:15 AM
> > > > *To:* Scott Morris
> > > > *Cc:* Joseph Brunner; Ananth Vk; ccielab@groupstudy.com
> > > > *Subject:* Re: Query : Network Types
> > > >
> > > >
> > > > Scott,
> > > > I hope your last response was not a Joke ;-) I know you
> > > like to
> > > > joke sometimes........
> > > >
> > > > There are 5 different type of network types under ospf namely:
> > > >
> > > > 1. broadcast
> > > > 2. non-broadcast
> > > > 3. point-to-point
> > > > 4. point-to-multipoint
> > > > 5. point-to-multipoint non-broadcast
> > > >
> > > > One can not simply use 5+4+3+2+1 logic or any other mathematical
> > > logic to
> > > > figure out what possible combinations are possible. Every network
> > > type under
> > > > ospf has certain characteristics(DR/BDR,Hello,Dead interval,etc).
> > > For ospf
> > > > to form adjacency with neighbors certain conditions must be met or
> > > else no
> > > > relationship would be formed. Additionally, as per Cisco Routing and
> > > > Switching official exam guide, it is not recommended to form
> > > neighbor
> > > > relationship between ospf network types requiring a DR/BDR and
> > > network types
> > > > that do not require a DR/BDR in NBMA networks even though the
> > > neighbor
> > > > relation comes up after fine tuning the Hello/Dead intervals.
> > > >
> > > >
> > > http://books.google.com/books?id=dKzpj4r7KCwC&pg=PA270&lpg=PA270&dq=nbma+ospf+network+type&source=web&ots=qLxQS3ST7M&sig=VpZJ06-c7z-fn6wz4MPb8Ocwk-U
> > > >
> > > >
> > > > HTH,
> > > > Tarun Pahuja
> > > > CCIE#7707(R&S,Security,SP,Voice,Storage),CCSI
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > On 10/22/07, Scott Morris < smorris@ipexpert.com> wrote:
> > > > >
> > > > > It's just math. 5+4+3+2+1 I didn't spend any time thinking more
> > > about
> > > > > what
> > > > > things would/wouldn't change. That's the part about studying. :)
> > >
> > > > >
> > > > > -----Original Message-----
> > > > > From: Joseph Brunner [mailto:joe@affirmedsystems.com ]
> > > > > Sent: Monday, October 22, 2007 10:45 AM
> > > > > To: 'Scott Morris'; 'Ananth Vk'; ccielab@groupstudy.com
> > > > > Subject: RE: Query : Network Types
> > > > >
> > > > > Scott is that 15 number including when we use 2 network types that
> > > > > do/don't
> > > > > require a dr and change the timers?
> > > > >
> > > > > -Joe
> > > > >
> > > > > -----Original Message-----
> > > > > From: nobody@groupstudy.com [mailto: nobody@groupstudy.com] On
> > > Behalf Of
> > > > > Scott Morris
> > > > > Sent: Monday, October 22, 2007 10:20 AM
> > > > > To: 'Ananth Vk'; ccielab@groupstudy.com
> > > > > Subject: RE: Query : Network Types
> > > > >
> > > > > As long as you have labbed those up and SEEN how things work,
> > > you'll
> > > > > have no
> > > > > worry about the order or combination or anything.
> > > > >
> > > > > There are 5 network types:
> > > > >
> > > > > 1. broadcast
> > > > > 2. non-broadcast
> > > > > 3. point-to-point
> > > > > 4. point-to-multipoint
> > > > > 5. point-to-multipoint non-broadcast
> > > > >
> > > > > If you are aware of the details of each, you'll be
> > > > > fine. Mathematically,
> > > > > there are 15 different combinations you can come up with.
> > > > >
> > > > > HTH,
> > > > >
> > > > >
> > > > > Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider)
> > > #4713,
> > > > > JNCIE-M
> > > > > #153, JNCIS-ER, CISSP, et al.
> > > > > CCSI/JNCI-M/JNCI-ER
> > > > > VP - Technical Training - IPexpert, Inc.
> > > > > IPexpert Sr. Technical Instructor
> > > > >
> > > > > A Cisco Learning Partner - We Accept Learning Credits!
> > > > >
> > > > > smorris@ipexpert.com
> > > > >
> > > > > Telephone: +1.810.326.1444
> > > > > Fax: +1.810.454.0130
> > > > > http://www.ipexpert.com
> > > > >
> > > > >
> > > > > -----Original Message-----
> > > > > From: nobody@groupstudy.com [mailto: nobody@groupstudy.com] On
> > > Behalf Of
> > > > > Ananth Vk
> > > > > Sent: Monday, October 22, 2007 5:31 AM
> > > > > To: ccielab@groupstudy.com
> > > > > Subject: Query : Network Types
> > > > >
> > > > > Hi
> > > > >
> > > > > I just wanted to confirm that these are the following network
> > > types
> > > > > regardless of layer 3 protocol
> > > > >
> > > > > 1. point to point - serial point to point links
> > > > >
> > > > > 2. broadcast - lan
> > > > >
> > > > > 3. NBMA (FR/ATM/etc)
> > > > >
> > > > > A. Pure Point-to-Point Configuration (each VC on a separate
> > > > > subinterface)
> > > > >
> > > > > B. Pure Multipoint Configuration (no subinterfaces)
> > > > >
> > > > > C. Hybrid Configuration (point-to-point and multipoint
> > > subinterfaces)
> > > > >
> > > > > I got this from a cisco link, is this the right order/fashion that
> > > i
> > > > > should
> > > > > remember / is there a different perspective ?
> > > > >
> > > > > Pls advice !
> > > > >
> > > > >
> > > > > Thanks
> > > > > Ananth
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