some questions on switches and hubs and routers... - TCP-IP

This is a discussion on some questions on switches and hubs and routers... - TCP-IP ; Hi. Im learning thingds about switches and hubs and routers. I have this picture http://img148.imageshack.us/img148/7541/red15ua.jpg a) If A sends data to G, which stations receive a copy ? My answer: I think D,E and G, but only G station will ...

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  1. some questions on switches and hubs and routers...

    Hi. Im learning thingds about switches and hubs and routers. I have this
    picture

    http://img148.imageshack.us/img148/7541/red15ua.jpg

    a) If A sends data to G, which stations receive a copy ?

    My answer: I think D,E and G, but only G station will pass data to upper
    level.

    b) If B starts to send data to E and at the same time D starts to send
    data to F, will be there collision ?

    My answer: I think so, because Switch A and station D are connected to a
    Hub, so they are on same collision domain. When switch re-send data it
    can collision with D.

    c) B start to send data to E, and at the same time C starts to send data
    to G, will be there a collision ?

    My answer: I dont think so, because B and C are connected to a switch,
    and all computers connected to a switch can start transkissions
    simultaneously, because switch separates collision domains. In this
    example, switch A will send first data from B, and after that data from C.


    d) On this picture

    http://img110.imageshack.us/img110/927/red23zf.jpg

    Id A sends an Ethernet broadcast, what stattions will receive a copy of
    that broadcast ?

    My answer: I think A,B,C,D,E Because router stops broadcast data.
    But I doubt if A station will also receive a copy of its own broadcast
    message.

    Any suggestion on these questions ???

    Thanks
    Johnny

  2. Re: some questions on switches and hubs and routers...

    On Sat, 17 Jun 2006 17:24:19 +0200, johnny wrote:

    > Hi. Im learning thingds about switches and hubs and routers. I have this
    > picture
    >
    > http://img148.imageshack.us/img148/7541/red15ua.jpg


    I think you uploaded the wrong picture. Your answers are sensible (and
    correct), but only if C is connected to the same switch as A and B are.

    M4
    --
    Redundancy is a great way to introduce more single points of failure.


  3. Re: some questions on switches and hubs and routers...

    Martijn Lievaart escribió:
    > On Sat, 17 Jun 2006 17:24:19 +0200, johnny wrote:
    >
    >> Hi. Im learning thingds about switches and hubs and routers. I have this
    >> picture
    >>
    >> http://img148.imageshack.us/img148/7541/red15ua.jpg

    >
    > I think you uploaded the wrong picture. Your answers are sensible (and
    > correct), but only if C is connected to the same switch as A and B are.
    >
    > M4

    ok you are correct, correct image is

    http://img218.imageshack.us/img218/8020/red10zx.jpg

    Are my answers correct ?

  4. Re: some questions on switches and hubs and routers...

    On Sat, 17 Jun 2006 19:24:47 +0200, johnny wrote:

    > ok you are correct, correct image is
    >
    > http://img218.imageshack.us/img218/8020/red10zx.jpg
    >
    > Are my answers correct ?


    As far as I can see, yes, absolutely spot on.

    M4
    --
    Redundancy is a great way to introduce more single points of failure.


  5. Re: some questions on switches and hubs and routers...


    johnny wrote:
    > Hi. Im learning thingds about switches and hubs and routers. I have this
    > picture
    >
    > http://img148.imageshack.us/img148/7541/red15ua.jpg
    >
    > a) If A sends data to G, which stations receive a copy ?
    >
    > My answer: I think D,E and G, but only G station will pass data to upper
    > level.
    >
    > b) If B starts to send data to E and at the same time D starts to send
    > data to F, will be there collision ?
    >
    > My answer: I think so, because Switch A and station D are connected to a
    > Hub, so they are on same collision domain. When switch re-send data it
    > can collision with D.
    >
    > c) B start to send data to E, and at the same time C starts to send data
    > to G, will be there a collision ?
    >
    > My answer: I dont think so, because B and C are connected to a switch,
    > and all computers connected to a switch can start transkissions
    > simultaneously, because switch separates collision domains. In this
    > example, switch A will send first data from B, and after that data from C.
    >
    >


    I agree with all that.

    > d) On this picture
    >
    > http://img110.imageshack.us/img110/927/red23zf.jpg
    >
    > Id A sends an Ethernet broadcast, what stattions will receive a copy of
    > that broadcast ?
    >
    > My answer: I think A,B,C,D,E Because router stops broadcast data.
    > But I doubt if A station will also receive a copy of its own broadcast
    > message.
    >


    for part d
    I am not sure if A will receive it. I've always read that the packet
    is received by all nodes. Though i'm not sure either. And there's a
    significant problem with that. If it were really the case that
    broadcasts were broadcast to all nodes, then there'd be an endless
    loop.
    so perhaps the originating device is exempted. I wonder if the source
    is hecked at the data link layer? or if it works like a hub(some
    electrical wizardry exempts the sender).


    regarding a hub - , i've read that a hub resends the signal to all
    devices except the device that originated the signal.

    The rest of your answers seem right.
    I share your doubts with part d.

    Out of interest, what book is that exercise from?

    Also, regarding devices receiving their own signal, there's a case
    where it happens, but the device receives it from itself, not from a
    repeater/hub.

    devices connected to a hub must run half duplex, so the devices enable
    their loopback circuits, these actually feed the sending device the
    signal it is sending. If the device then receives a signal over that
    one (from outside), then it detects a collision(detection is plain
    electricity e.g. current-amps- too high) .


    I find Part d is puzzling too, ?
    also
    Is that signal received through loopback then passed up as far as the
    data link layer and rejected? maybe somebody here knows for sure?


  6. Re: some questions on switches and hubs and routers...


    q_q_anonymous@yahoo.co.uk wrote:
    > johnny wrote:
    > > Hi. Im learning thingds about switches and hubs and routers. I have this
    > > picture
    > >
    > > http://img148.imageshack.us/img148/7541/red15ua.jpg
    > >
    > > a) If A sends data to G, which stations receive a copy ?
    > >
    > > My answer: I think D,E and G, but only G station will pass data to upper
    > > level.
    > >
    > > b) If B starts to send data to E and at the same time D starts to send
    > > data to F, will be there collision ?
    > >
    > > My answer: I think so, because Switch A and station D are connected to a
    > > Hub, so they are on same collision domain. When switch re-send data it
    > > can collision with D.
    > >
    > > c) B start to send data to E, and at the same time C starts to send data
    > > to G, will be there a collision ?
    > >
    > > My answer: I dont think so, because B and C are connected to a switch,
    > > and all computers connected to a switch can start transkissions
    > > simultaneously, because switch separates collision domains. In this
    > > example, switch A will send first data from B, and after that data from C.
    > >
    > >

    >
    > I agree with all that.
    >
    > > d) On this picture
    > >
    > > http://img110.imageshack.us/img110/927/red23zf.jpg
    > >
    > > Id A sends an Ethernet broadcast, what stattions will receive a copy of
    > > that broadcast ?
    > >
    > > My answer: I think A,B,C,D,E Because router stops broadcast data.
    > > But I doubt if A station will also receive a copy of its own broadcast
    > > message.
    > >

    >
    > for part d
    > I am not sure if A will receive it. I've always read that the packet
    > is received by all nodes. Though i'm not sure either. And there's a
    > significant problem with that. If it were really the case that
    > broadcasts were broadcast to all nodes, then there'd be an endless
    > loop.
    > so perhaps the originating device is exempted. I wonder if the source
    > is hecked at the data link layer? or if it works like a hub(some
    > electrical wizardry exempts the sender).
    >
    >
    > regarding a hub - , i've read that a hub resends the signal to all
    > devices except the device that originated the signal.
    >
    > The rest of your answers seem right.
    > I share your doubts with part d.
    >
    > Out of interest, what book is that exercise from?
    >
    > Also, regarding devices receiving their own signal, there's a case
    > where it happens, but the device receives it from itself, not from a
    > repeater/hub.
    >
    > devices connected to a hub must run half duplex, so the devices enable
    > their loopback circuits, these actually feed the sending device the
    > signal it is sending. If the device then receives a signal over that
    > one (from outside), then it detects a collision(detection is plain
    > electricity e.g. current-amps- too high) .
    >
    >
    > I find Part d is puzzling too, ?
    > also
    > Is that signal received through loopback then passed up as far as the
    > data link layer and rejected? maybe somebody here knows for sure?



    You wrote
    > > Id A sends an Ethernet broadcast, what stattions will receive a copy of
    > > that broadcast ?
    > >
    > > My answer: I think A,B,C,D,E Because router stops broadcast data.
    > > But I doubt if A station will also receive a copy of its own broadcast
    > > message.
    > >


    It's B,C,D,E . A will not be sent a copy of its the broadcast
    message.

    it's not just that A was the original. It works between any pair. W
    sent to X. if X sends to Y, Y will not send back to X. (and of course
    X not back to W)

    A broadcast is not sent back down the "link" /cable/segment that
    originated it. i.e. not sent back to the immediate device that sent it.
    Otherwise you'd have loops.

    I don't know if that is dealt with at the physical layer(as a repeater
    hub does) or at the data link layer.

    Here are some quotes to back that up
    curvy brackets {{ ... }} are my own


    RFC 922

    Since broadcasting is not
    covered in the basic IP specification [12] {{this is referring to
    RFC 791}}, there is no agreed-upon way to do it, and so protocol
    designers have not made use of it. (The
    issue has been touched upon before, e.g. [6], but has not been the
    subject of a standard.)

    ....

    The primary rule for avoiding loops is "never broadcast a
    datagram on the hardware network it was received on". It is
    not sufficient simply to avoid repeating datagram that a
    gateway has heard from itself; this still allows loops if
    there are several gateways on a hardware network.

    ...
    there is also an algorithm.


    Also
    RFC 1122
    Any host that forwards datagrams generated by another host is
    acting as a gateway and MUST also meet the specifications laid
    out
    in the gateway requirements RFC


    {{generally, i think IP broadcasts aren't forwarded though. RFC 1812
    would have more details on wheter ot not they are forwarded. and diff
    types of IP broadcasts. Either way, they're never forwarded to the
    originating link.

    I saw nothing in RFC 1122 dealing with loops either. But RFC 922
    mentions it and answers the problem you had with part d.}}


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