I know I'm being picky, but I find the question very
confusing. My main gripe with it is that the frame
sent from comp 1 is not the same frame as that which
is re-transmitted on segment B due to the collision.
i.e different CRC due to possibilities such as changes
to TTL etc.
So I would still like to offer the arument that Router
B does not re-transmit the original frame from comp 1
on seg A but DOES re-transmit the frame that had a
collision on seg B.
Regards,
Phil.
--- Dale Holmes <[EMAIL PROTECTED]> wrote: >
Well,
>
> You are right that the router and the other device
> that transmits (resulting
> in a collision) will both do a random back-off and
> re-transmit, but in the
> question it is the frame carrying the message from
> Computer 1 that we are
> concerned with.
>
> The questions asks who will retransmit that frame -
> with the possible
> answers being router B (the correct answer), Router
> A, Computer 1, or
> Computer 2 (which is the intended recipient and so
> cannot "re-transmit"
> since in this context it never tranamitted anything
> in the first place...
>
> You cannot assume that there are no other hosts on
> segment B, though in this
> case it really does not matter whose frame collides
> with Router B's frame,
> only that Router B detects the collision and
> retransmits.
>
> I hope that this helps.
>
> PS - this may or may not be an actual exam question,
> but there will be a
> number of questions on the exam that are very
> similar. Be prepared to know
> who will do the retransmit under any giver
> circumstance and what the layer 2
> and layer 3 addresses will be. Good Luck!
>
> Dale
> [=`)
>
> >From: Phil Barker <[EMAIL PROTECTED]>
> >Reply-To: Phil Barker <[EMAIL PROTECTED]>
> >To: Priscilla Oppenheimer <[EMAIL PROTECTED]>,
> Derek Chung
> ><[EMAIL PROTECTED]>, [EMAIL PROTECTED]
> >Subject: Re: CCIE Questions... Answer to Q3 ???
> >Date: Tue, 19 Sep 2000 19:08:22 +0100 (BST)
> >
> >I havn't read this thread so apologies if this has
> >been done already.
> >
> >Computer 1 sends to Computer 2.
> >
> >Router B relays a valid frame to computer 2.
> >Assume no other devices on Segment B for clarity,
> >computer 2 must be transmitting a frame on this
> >segment in order for the collision to occur.
> >
> >Therefore router B and computer 2 do a random
> back-off
> >
> >before attempting to re-transmit. So shouldn't the
> >answer to which device re-transmits be "either"
> >depending on which device can respond the fastest ?
> >
> >i.e Router B's frame is totally independent from
> >Computer 2's frame.
> >
> >Regards,
> >
> >Phil.
> >
> >PS : hope thats not a real CCIE question or I think
> >I'll be throwing tantrums on the day .......
> >
> >
> >
> >
> >--- Priscilla Oppenheimer <[EMAIL PROTECTED]>
> wrote:
> > > Where did these questions come from? Please
> specify
> > > the source (book, etc.)
> > > so that we know we aren't disobeying the NDA and
> > > giving you answers from an
> > > actual test. These sure sound like questions
> from
> > > the CCIE written. Also, I
> > > think it would be best to limit each e-mail
> message
> > > to one topic. It makes
> > > discussions easier to follow.
> > >
> > > Despite all that, I can't resist giving you my
> > > answers! &;-) See below.
> > >
> > > At 05:18 AM 9/17/00, Derek Chung wrote:
> > > >Question 1:
> > > >Router A and Router B are configured to route
> IP to
> > > each other over a serial
> > > >line. Host A is connected to Router A and Host
> B is
> > > connected to Router B. A
> > > >packet is sent from Host A to host B. A hit on
> the
> > > serial line causes an
> > > >error in the packet. Retransmission is sent by:
> > >
> > > Host A retransmits the packet. The data-link
> layer
> > > protocols in use today
> > > on serial lines, including PPP, Frame Relay, and
> > > Cisco HDLC, detect errors
> > > but are not responsible for error correction or
> > > retransmission.
> > >
> > >
> > > >Question 2:
> > > >During the middle of a TCP conversion across a
> > > routed backbone, the network
> > > >receives a voltage spike and several of the
> packets
> > > are damaged. Where are
> > > >the packets retransmitted from?
> > >
> > > The TCP sender. This is almost a repeat of the
> last
> > > question.
> > >
> > >
> > > >Question 3:
> > > >Computer1 --------[Segment
> > >
> >
>
>A]-------RouterA--------------RouterB----------[SegmentB]--------------Compu
> > > >ter2
> > > >A packet is sent to Computer 2 from Computer 1.
> A
> > > collision occurs on
> > > >Segment B. Which device will retransmit the
> frame
> > > and what will the source
> > > >MAC address be (when the packet actually
> reaches
> > > Segment B)?
> > >
> > > Router B senses the collision and retransmits at
> the
> > > MAC layer. The MAC
> > > address is Router B's Ethernet address.
> > >
> > >
> > > >Question 4:
> > > >When computer A sends a frame to computer B
> across
> > > many routers, how will
> > > >the source and destination layer 3 addresses
> > > change? How will the source and
> > > >destination layer 2 addresses change?
> > >
> > > Layer 3 addresses won't change (unless you have
> NAT
> > > or tunnelling or
> > > something else bizarre.) The Layer 2 addresses
> > > change each time a router
> > > re-encapsulates the packet in a data-link-layer
> > > header than includes
> > > layer-2 addresses.
> > >
> > > Priscilla
> > >
> > > ________________________
> > >
> > > Priscilla Oppenheimer
> > > http://www.priscilla.com
> > >
> > > **NOTE: New CCNA/CCDA List has been formed. For
> more
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