Definately a good point, although RIP uses UDP port 520 and EIGRP
uses multicast port 224.0.0.10. Multicast packets are baesd on UDP.
I wasn't thinking ICMP and IGMP...
""joel.studtmann"" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Actually, I never specified that the packet in questioin number 1 had to
be
> UDP. Question 1 only specifies that the routers are routing IP. It could
> be an ICMP, IGMP, RIP, EIGRP, etc... packet. Not all IP packets use a
> transport protocol. Granted, 99% of user traffic does, but the question
> doesn't specify. I'm just not completely familiar with all of the
possible
> data-link protocols available over a serial link, and which ones (if any)
> would detect the bad packet and have the last station retransmit. I think
> x25 would, as its overengineered for providing error-checking, and think
PPP
> might.
>
> Joel Studtmann
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
> Ed
> Sent: Sunday, September 17, 2000 7:16 PM
> To: [EMAIL PROTECTED]
> Subject: Re: CCIE Questions...
>
>
> I agree with your answers excpet for #1. Just because a transport layer
> protocol hasn't been specified, I don't think we can assume UDP. I would
> have to guess that the original host retransmits. I don't think the
router
> would,
> since it doesn't care about anything above the 3rd layer unless otherwise
> configured with QOS type stuff...
>
> Ed
> ""joel.studtmann"" <[EMAIL PROTECTED]> wrote in message
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > Replying out of order:
> >
> > Question 2) Packet is damaged and has a bad CRC at the datalink layer,
so
> > is dropped by next switch or router or end PC that verifies the CRC. (A
> hub
> > wouldn't notice). Retransmission is sent from the original source (IP
> host)
> > after not receiving an acknowledgement for that packet from the
> destination.
> >
> > Question 3) Collison occurs, and is detected by Router B. Router B
then
> > retransmits the packet. Source MAC address will be Router B, as the
> router
> > changes the source MAC to itself and the destination to the next hop.
(In
> > this case, computer 2)
> >
> > Question 4) Layer 3 sources and destinations will not change.
(Ignoring
> > issues such as NAT here, for simplicity). Layer 2 MAC addresses will
> change
> > whenever the packet crosses a layer-3 device, as the router removes the
> old
> > datalink information, examines the layer 3 information, and repackages
the
> > packet for the next hop device, changing the destination MAC address to
> the
> > next hop and the source MAC address to itself.
> >
> > Back to Question 1) My first answer is that the packet is simply lost.
> The
> > protocol is simply IP, which provides best-effort delivery, and wouldn't
> be
> > retransmitted by the host (assuming it's not a TCP packet). I'm not
> > completely familiar with all types of serial line encapsulations, but I
> > believe it would be retransmitted by the router if it was over an x25
> link.
> > Possibly PPP as well. Not really sure: What's the answer?
> >
> > My two bits,
> >
> > Joel Studtmann
> >
> >
> >
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
> > Derek Chung
> > Sent: Sunday, September 17, 2000 2:19 PM
> > To: [EMAIL PROTECTED]
> > Subject: CCIE Questions...
> >
> >
> > 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:
> >
> > 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?
> >
> > 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)?
> >
> > 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?
> >
> >
> >
> >
> > **NOTE: New CCNA/CCDA List has been formed. For more information go to
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