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
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