From: Tarun Pahuja (pahujat@gmail.com)
Date: Wed Oct 24 2007 - 07:52:23 ART
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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