Some other station could send the directed broadcast. I could be sitting
out here on network 36.0.0.0 or whatever and send to 172.18.3.255, the
example in the test question. If a classful routing protocol were in use
and had summarized, then routers would simply forward over to 172.18.0.0.
Then a router sitting on that network would know that the subnet mask is
really 255.255.254.0 and would send the broadcast out just the one
interface in the 172.18.1.0 subnet.
It is getting late. I hope that made some sense.
Most routers these days are configured with no ip directed broadcast, so
the packet would get dropped, but that's beside the point.
The real point was that Howard wrote the question, and he adds a statement
about classless or classful to make a point. See his message....
Priscilla
At 01:12 AM 7/25/01, Ole Drews Jensen wrote:
>It is now almost midnight, and I realize that the reason for this question
>could be a temporarily black hole in my head, but here it is anyway.
>
>Since we're talking about a directed broadcast address for a network - when
>does a Cisco router actually use that address?
>
>When I assign an IP address to any interface, that be ethernet, tokenring,
>serial or loopback, the result I get from a SHOW IP INT always tells me that
>the broadcast address for that network is 255.255.255.255.
>
>Am I just being too tired, or what's going on here?
>
>Thanks,
>
>Ole
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Ole Drews Jensen
> Systems Network Manager
> CCNA, MCSE, MCP+I
> RWR Enterprises, Inc.
> [EMAIL PROTECTED]
> http://www.RouterChief.com
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> NEED A JOB ???
> http://www.oledrews.com/job
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>
>-----Original Message-----
>From: Leigh Anne Chisholm [mailto:[EMAIL PROTECTED]]
>Sent: Tuesday, July 24, 2001 11:30 PM
>To: [EMAIL PROTECTED]
>Subject: RE: ccna challenge question [7:13565]
>
>
>The term "classful" could have been thrown in for two reasons. 1, as you
>suggest, is to lead the reader to think about "classful". Do they really
>understand the concept? If they don't, they'd likely select a broadcast of
>172.18.255.255. The other is that it may have been a leftover from a
>similar question where the question was changed just enough so that the
>phrase really didn't apply.
>
>I guess the definitive answer about the CertificationZone question of the
>week for last week would really be to find out who wrote the question, and
>ask what their thinking was at the time. I just checked my files--it wasn't
>one of mine so I can't say one way or the other...
>
>-----Original Message-----
>From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
>Guy Russell
>Sent: Tuesday, July 24, 2001 8:33 PM
>To: [EMAIL PROTECTED]
>Subject: Re: ccna challenge question [7:13565]
>
>
>Yes, I agree....
>
>But why the bit about Classful. It seemed whoever wrote the question wanted
>it to be an issue about the "Classful" idea.
>
>Normally, I would fully agree, but if this was a Cisco test question,
>especially since the way they word some questions, how would you answer...
>
>I agree with both points!!!
>
>But again take a look at the term classful. When do we see it...
>
>Now lets break down the question...
>
>Using Classful assumptions, what is the directed broadcast address for
>172.18.2.0 with the mask of 255.255.254.0?
>
>Now clearly, it says... Using classful assumptions....
>
>At first glance it appears to be a simple subnetting question where we would
>try to find the network and broadcast address. So in that case we would come
>up with...
>
>172.18.2.0 as the network ID and 172.18.3.255 as the broadcast...
>
>But thats too easy... if we were sitting at a 100.00 test, we would have to
>rethink...
>
>Now, again if we were sitting at a CCNA test, we would see 2 correct answers
>for either way we went. Cisco isnt like that... SO I personally would be
>inclined to think its a test to see if we know the difference between
>classless ans classful routing.
>
>Again, only if this was an actual test question!!! If this was something
>someone asked me off the top of my head, I would agree, but it is a
>challenge question....
>
>
>
>
>----- Original Message -----
>From: "Leigh Anne Chisholm"
>To:
>Sent: Tuesday, July 24, 2001 7:10 PM
>Subject: RE: ccna challenge question [7:13565]
>
>
> > Classful addressing doesn't mean that routers do not look at the subnet
> > mask. Au contraire! Routers ALWAYS are concerned with subnet mask
> > information!
> >
> > Classful addressing just means that a router that receives a routing
>update
> > for a network for which it does not have a directly connected interface
>will
> > assume the standard classful subnet mask. In the case of a router that
>does
> > have a directly connected interface that is using a subnet mask that is
> > borrowing bits from the host portion of the mask, it applies that mask to
> > the advertised network information. Variable subnet masking (subnet
masks
> > of different lengths - /25, /26, /27 used in conjunction with the same
> > network) is not supported.
> >
> >
> > -- Leigh Anne
> >
> > At 05:48 PM 7/24/01, Guy Russell wrote:
> > >Actually I disagree...
> > >
> > >Routers using Classful addresses, do not look at the subnet mask, nor do
> > >they transmit the subnet mask...Since the term classful was used, we
>would
> > >obviously be talking about the routing protocol, so a broadcast would be
> > >based only on the first octet to decide.
> > >
> > >Now a machine is not dependent on classful, it understands its own
subnet
> > >mask, and then the answer would be that... But the term Classful negates
> > >that theory of it being a computer or other host...
> > >
> > >
> > >
> > >----- Original Message -----
> > >From: Priscilla Oppenheimer
> > >To:
> > >Sent: Tuesday, July 24, 2001 5:28 PM
> > >Subject: Re: ccna challenge question [7:13565]
> > >
> > >
> > > > At 04:28 PM 7/24/01, Ed Moss wrote:
> > > > >The key in the question is the word "classful".
> > > >
> > > > Classful doesn't mean it has to end on an 8-bit boundary.
> > > >
> > > > >This is a Class B address
> > > > >with a 16 bit classful mask.
> > > >
> > > > It's not 16-bit. It says the mask is 255.255.254.0. That's 23 bits in
> > the
> > > > prefix (network) part.
> > > >
> > > > The answer is B. Put it in binary to understand it.....
> > > >
> > > > Priscilla
> > > >
> > > > >I would have to say the correct answer would
> > > > >be 'C' 172.18.255.255.
> > > > >Ed
> > > > >
> > > > > > Using classful assumptions, what is the directed broadcast
address
> > for
> > > > > > 172.18.2.0 with the mask 255.255.254.0?
> > > > > > a) 172.18.2.255
> > > > > > b) 172.18.3.255
> > > > > > c) 172.18.255.255
> > > > > > d) 172.18.0.0
> > > > >
> > > > > > Answer
> > > > > > b)
> > > > ________________________
> > > >
> > > > Priscilla Oppenheimer
> > > > http://www.priscilla.com
> > ________________________
> >
> > Priscilla Oppenheimer
> > http://www.priscilla.com
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=13718&t=13565
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