An OSPF question

Discussion in 'Cisco' started by aaabbb16@hotmail.com, Sep 12, 2008.

  1. Guest

    I config. ospf between two routers. (point to point).
    I use "broadcast" parameter. It does not work, then
    back to "point to point" it works.
    I curious that how router know it connect to p2p or broadcast.
    I don't think it based on full duplex.

    TIA,
    s
     
    , Sep 12, 2008
    #1
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  2. wrote:
    > I config. ospf between two routers. (point to point).
    > I use "broadcast" parameter. It does not work, then
    > back to "point to point" it works.
    > I curious that how router know it connect to p2p or broadcast.
    > I don't think it based on full duplex.
    >
    > TIA,
    > s


    But router knows interface type, of course. serial interfaces are treated as p2p
    , ethernet as broadcast, e.g.
     
    Andre Wisniewski, Sep 13, 2008
    #2
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  3. Guest

    On 9ÔÂ13ÈÕ, ÉÏÎç3ʱ44·Ö, Andre Wisniewski <> wrote:
    > wrote:
    > > I config. ospf between two routers. (point to point).
    > > I use "broadcast" parameter. It does not work, then
    > > back to "point to point" it works.
    > > I curious that how router know it connect to p2p or broadcast.
    > > I don't think it based on full duplex.

    >
    > > TIA,
    > > s

    >
    > But router knows interface type, of course. serial interfaces are treated as p2p
    > , ethernet as broadcast, e.g.


    Thanks, I use fast ethernet.
     
    , Sep 13, 2008
    #3
  4. Stephen Guest

    On Sat, 13 Sep 2008 07:15:59 -0700 (PDT), wrote:

    >On 9??13??, ????3??44??, Andre Wisniewski <> wrote:
    >> wrote:
    >> > I config. ospf between two routers. (point to point).
    >> > I use "broadcast" parameter. It does not work, then
    >> > back to "point to point" it works.
    >> > I curious that how router know it connect to p2p or broadcast.
    >> > I don't think it based on full duplex.

    >>
    >> > TIA,
    >> > s

    >>
    >> But router knows interface type, of course. serial interfaces are treated as p2p
    >> , ethernet as broadcast, e.g.

    >
    >Thanks, I use fast ethernet.


    Broadcast should work over Ethernet - as long as both ends are
    conifgured consistently. Make sure they are both in the same subnet,
    same mask, same area.

    you may want to turn on more detailed OSPF logging to see if there are
    any diagnostics available via the internal log.
    --
    Regards

    - replace xyz with ntl
     
    Stephen, Sep 14, 2008
    #4
  5. Guest

    On 9ÔÂ14ÈÕ, ÉÏÎç1ʱ41·Ö, Stephen <> wrote:
    > On Sat, 13 Sep 2008 07:15:59 -0700 (PDT), wrote:
    > >On 9??13??, ????3??44??, Andre Wisniewski <> wrote:
    > >> wrote:
    > >> > I config. ospf between two routers. (point to point).
    > >> > I use "broadcast" parameter. It does not work, then
    > >> > back to "point to point" it works.
    > >> > I curious that how router know it connect to p2p or broadcast.
    > >> > I don't think it based on full duplex.

    >
    > >> > TIA,
    > >> > s

    >
    > >> But router knows interface type, of course. serial interfaces are treated as p2p
    > >> , ethernet as broadcast, e.g.

    >
    > >Thanks, I use fast ethernet.

    >
    > Broadcast should work over Ethernet - as long as both ends are
    > conifgured consistently. Make sure they are both in the same subnet,
    > same mask, same area.
    >
    > you may want to turn on more detailed OSPF logging to see if there are
    > any diagnostics available via the internal log.
    > --
    > Regards
    >
    > - replace xyz with ntl- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
    >
    > - ÏÔʾÒýÓõÄÎÄ×Ö -


    Thanks,
    I may not give a good descrption of my question.
    Two routers (not cisco) direct connect via fast ethernet using ospf.
    How do the routers know it is broadcast or p2p?
    TIA,
    /s
     
    , Sep 14, 2008
    #5
  6. wrote:
    > On 9ÔÂ14ÈÕ, ÉÏÎç1ʱ41·Ö, Stephen <> wrote:
    >> On Sat, 13 Sep 2008 07:15:59 -0700 (PDT), wrote:
    >>> On 9??13??, ????3??44??, Andre Wisniewski <> wrote:
    >>>> wrote:
    >>>>> I config. ospf between two routers. (point to point).
    >>>>> I use "broadcast" parameter. It does not work, then
    >>>>> back to "point to point" it works.
    >>>>> I curious that how router know it connect to p2p or broadcast.
    >>>>> I don't think it based on full duplex.
    >>>>> TIA,
    >>>>> s
    >>>> But router knows interface type, of course. serial interfaces are treated as p2p
    >>>> , ethernet as broadcast, e.g.
    >>> Thanks, I use fast ethernet.

    >> Broadcast should work over Ethernet - as long as both ends are
    >> conifgured consistently. Make sure they are both in the same subnet,
    >> same mask, same area.
    >>
    >> you may want to turn on more detailed OSPF logging to see if there are
    >> any diagnostics available via the internal log.
    >> --
    >> Regards
    >>
    >> - replace xyz with ntl- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
    >>
    >> - ÏÔʾÒýÓõÄÎÄ×Ö -

    >
    > Thanks,
    > I may not give a good descrption of my question.
    > Two routers (not cisco) direct connect via fast ethernet using ospf.
    > How do the routers know it is broadcast or p2p?
    > TIA,
    > /s
    >


    Once again, router knows which interface is installed.

    If router detects an ethernet interface it knows that a broadcastable medium is
    connected. Broadcast is essential for ethernet.

    If router detects an serial interface it knows there is no broacastable medium.

    If your questions refers to configuration statement "ip ospf network broadcast"
    have a look at this great document
    http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml

    Especially pay attention on sections Neighbors and Adjacencies. It's all
    explained herein very well.

    Andre
     
    Andre Wisniewski, Sep 15, 2008
    #6
  7. Guest

    On 9ÔÂ15ÈÕ, ÉÏÎç10ʱ49·Ö, Andre Wisniewski <> wrote:
    > wrote:
    > > On 9ÔÂ14ÈÕ, ÉÏÎç1ʱ41·Ö, Stephen <> wrote:
    > >> On Sat, 13 Sep 2008 07:15:59 -0700 (PDT), wrote:
    > >>> On 9??13??, ????3??44??, Andre Wisniewski <> wrote:
    > >>>> wrote:
    > >>>>> I config. ospf between two routers. (point to point).
    > >>>>> I use "broadcast" parameter. It does not work, then
    > >>>>> back to "point to point" it works.
    > >>>>> I curious that how router know it connect to p2p or broadcast.
    > >>>>> I don't think it based on full duplex.
    > >>>>> TIA,
    > >>>>> s
    > >>>> But router knows interface type, of course. serial interfaces are treated as p2p
    > >>>> , ethernet as broadcast, e.g.
    > >>> Thanks, I use fast ethernet.
    > >> Broadcast should work over Ethernet - as long as both ends are
    > >> conifgured consistently. Make sure they are both in the same subnet,
    > >> same mask, same area.

    >
    > >> you may want to turn on more detailed OSPF logging to see if there are
    > >> any diagnostics available via the internal log.
    > >> --
    > >> Regards

    >
    > >> - replace xyz with ntl- Òþ²Ø±»ÒýÓÃÎÄ×Ö -

    >
    > >> - ÏÔʾÒýÓõÄÎÄ×Ö -

    >
    > > Thanks,
    > > I may not give a good descrption of my question.
    > > Two routers (not cisco) direct connect via fast ethernet using ospf.
    > > How do the routers know it is broadcast or p2p?
    > > TIA,
    > > /s

    >
    > Once again, router knows which interface is installed.
    >
    > If router detects an ethernet interface it knows that a broadcastable medium is
    > connected. Broadcast is essential for ethernet.
    >
    > If router detects an serial interface it knows there is no broacastable medium.
    >
    > If your questions refers to configuration statement "ip ospf network broadcast"
    > have a look at this great documenthttp://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0...
    >
    > Especially pay attention on sections Neighbors and Adjacencies. It's all
    > explained herein very well.
    >
    > Andre- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
    >
    > - ÏÔʾÒýÓõÄÎÄ×Ö -


    Thanks, I have checked the cisco url you list above.
    There is a command to assign network type "ip ospf network {broadcast
    | non-
    broadecast | point to multipoint}
    My question is if two routers connected via ethernet, Do I should use
    broadcast
    or non-broadcast or either way?
    /s
     
    , Sep 15, 2008
    #7
  8. wrote:
    > On 9ÔÂ15ÈÕ, ÉÏÎç10ʱ49·Ö, Andre Wisniewski <> wrote:
    >> wrote:
    >>> On 9ÔÂ14ÈÕ, ÉÏÎç1ʱ41·Ö, Stephen <> wrote:
    >>>> On Sat, 13 Sep 2008 07:15:59 -0700 (PDT), wrote:
    >>>>> On 9??13??, ????3??44??, Andre Wisniewski <> wrote:
    >>>>>> wrote:
    >>>>>>> I config. ospf between two routers. (point to point).
    >>>>>>> I use "broadcast" parameter. It does not work, then
    >>>>>>> back to "point to point" it works.
    >>>>>>> I curious that how router know it connect to p2p or broadcast.
    >>>>>>> I don't think it based on full duplex.
    >>>>>>> TIA,
    >>>>>>> s
    >>>>>> But router knows interface type, of course. serial interfaces are treated as p2p
    >>>>>> , ethernet as broadcast, e.g.
    >>>>> Thanks, I use fast ethernet.
    >>>> Broadcast should work over Ethernet - as long as both ends are
    >>>> conifgured consistently. Make sure they are both in the same subnet,
    >>>> same mask, same area.
    >>>> you may want to turn on more detailed OSPF logging to see if there are
    >>>> any diagnostics available via the internal log.
    >>>> --
    >>>> Regards
    >>>> - replace xyz with ntl- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
    >>>> - ÏÔʾÒýÓõÄÎÄ×Ö -
    >>> Thanks,
    >>> I may not give a good descrption of my question.
    >>> Two routers (not cisco) direct connect via fast ethernet using ospf.
    >>> How do the routers know it is broadcast or p2p?
    >>> TIA,
    >>> /s

    >> Once again, router knows which interface is installed.
    >>
    >> If router detects an ethernet interface it knows that a broadcastable medium is
    >> connected. Broadcast is essential for ethernet.
    >>
    >> If router detects an serial interface it knows there is no broacastable medium.
    >>
    >> If your questions refers to configuration statement "ip ospf network broadcast"
    >> have a look at this great documenthttp://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0...
    >>
    >> Especially pay attention on sections Neighbors and Adjacencies. It's all
    >> explained herein very well.
    >>
    >> Andre- Òþ²Ø±»ÒýÓÃÎÄ×Ö -
    >>
    >> - ÏÔʾÒýÓõÄÎÄ×Ö -

    >
    > Thanks, I have checked the cisco url you list above.
    > There is a command to assign network type "ip ospf network {broadcast
    > | non-
    > broadecast | point to multipoint}
    > My question is if two routers connected via ethernet, Do I should use
    > broadcast
    > or non-broadcast or either way?
    > /s


    This command is used in interface configuration context and is used to change
    default interface network type. You don't need it. There's no difference between
    direct connected router or ones who are connected via a switch. Broadcast will
    work either.

    Andre
     
    Andre Wisniewski, Sep 16, 2008
    #8
  9. Stephen Guest

    On Mon, 15 Sep 2008 13:08:03 -0700 (PDT), wrote:

    >On 9??15??, ????10??49??, Andre Wisniewski <> wrote:
    >> wrote:
    >> > On 9??14??, ????1??41??, Stephen <> wrote:
    >> >> On Sat, 13 Sep 2008 07:15:59 -0700 (PDT), wrote:
    >> >>> On 9??13??, ????3??44??, Andre Wisniewski <> wrote:
    >> >>>> wrote:
    >> >>>>> I config. ospf between two routers. (point to point).
    >> >>>>> I use "broadcast" parameter. It does not work, then
    >> >>>>> back to "point to point" it works.
    >> >>>>> I curious that how router know it connect to p2p or broadcast.
    >> >>>>> I don't think it based on full duplex.
    >> >>>>> TIA,
    >> >>>>> s
    >> >>>> But router knows interface type, of course. serial interfaces are treated as p2p
    >> >>>> , ethernet as broadcast, e.g.
    >> >>> Thanks, I use fast ethernet.
    >> >> Broadcast should work over Ethernet - as long as both ends are
    >> >> conifgured consistently. Make sure they are both in the same subnet,
    >> >> same mask, same area.

    >>
    >> >> you may want to turn on more detailed OSPF logging to see if there are
    >> >> any diagnostics available via the internal log.
    >> >> --
    >> >> Regards

    >>
    >> >> - replace xyz with ntl- ?????????????? -

    >>
    >> >> - ?????????????? -

    >>
    >> > Thanks,
    >> > I may not give a good descrption of my question.
    >> > Two routers (not cisco) direct connect via fast ethernet using ospf.
    >> > How do the routers know it is broadcast or p2p?
    >> > TIA,
    >> > /s

    >>
    >> Once again, router knows which interface is installed.
    >>
    >> If router detects an ethernet interface it knows that a broadcastable medium is
    >> connected. Broadcast is essential for ethernet.
    >>
    >> If router detects an serial interface it knows there is no broacastable medium.
    >>
    >> If your questions refers to configuration statement "ip ospf network broadcast"
    >> have a look at this great documenthttp://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0...
    >>
    >> Especially pay attention on sections Neighbors and Adjacencies. It's all
    >> explained herein very well.
    >>
    >> Andre- ?????????????? -
    >>
    >> - ?????????????? -

    >
    >Thanks, I have checked the cisco url you list above.
    >There is a command to assign network type "ip ospf network {broadcast
    >| non-
    >broadecast | point to multipoint}
    >My question is if two routers connected via ethernet, Do I should use
    >broadcast
    >or non-broadcast or either way?
    >/s


    it depends.

    some boxes (not cisco AFAIR) do not allow you to choose, as they limit
    which options work on Ethernet.

    I have had major hassles with cisco to foundry links on GigE which
    will not work with some permutations of the choices - but do not
    bother to log why they do not form an adjacency......

    the "classic" argument is that point to point uses a bit less
    resources in the router, so is "better" if you have a router with lots
    of OSPF interface - but this needs more config.
    Reality is if you are that close to the edge, your network is already
    broken, but you havent provoked it enough yet......

    However - you imply this is "just point to point" - with many OSPF
    devices actually being switches and sometimes using adjacencies on
    VLANs, you can end up with more than 2 devices in a subnet even when
    all the pysical connections are point to point.
    Here, making a special case for when there are only 2 devices may make
    life more complicated.

    personally - mimimum config and being consistent seems to cause fewer
    problems so is the way to go. So - broadcast is my preferred setup.
    --
    Regards

    - replace xyz with ntl
     
    Stephen, Sep 16, 2008
    #9
  10. Merv Guest

    On Sep 16, 4:13 pm, Stephen <> wrote:
    > On Mon, 15 Sep 2008 13:08:03 -0700 (PDT), wrote:
    > >On 9??15??, ????10??49??, Andre Wisniewski <> wrote:
    > >> wrote:
    > >> > On 9??14??, ????1??41??, Stephen <> wrote:
    > >> >> On Sat, 13 Sep 2008 07:15:59 -0700 (PDT), wrote:
    > >> >>> On 9??13??, ????3??44??, Andre Wisniewski <> wrote:
    > >> >>>> wrote:
    > >> >>>>> I config. ospf between two routers. (point to point).
    > >> >>>>> I use "broadcast" parameter. It does not work, then
    > >> >>>>> back to "point to point" it works.
    > >> >>>>> I curious that how router know it connect to p2p or broadcast.
    > >> >>>>> I don't think it based on full duplex.
    > >> >>>>> TIA,
    > >> >>>>> s
    > >> >>>> But router knows interface type, of course. serial interfaces are treated as p2p
    > >> >>>> , ethernet as broadcast, e.g.
    > >> >>> Thanks, I use fast ethernet.
    > >> >> Broadcast should work over Ethernet - as long as both ends are
    > >> >> conifgured consistently. Make sure they are both in the same subnet,
    > >> >> same mask, same area.

    >
    > >> >> you may want to turn on more detailed OSPF logging to see if there are
    > >> >> any diagnostics available via the internal log.
    > >> >> --
    > >> >> Regards

    >
    > >> >> - replace xyz with ntl- ?????????????? -

    >
    > >> >> - ?????????????? -

    >
    > >> > Thanks,
    > >> > I may not give a good descrption of my question.
    > >> > Two routers (not cisco) direct connect via fast ethernet using ospf.
    > >> > How do the routers know it is broadcast or p2p?
    > >> > TIA,
    > >> > /s

    >
    > >> Once again, router knows which interface is installed.

    >
    > >> If router detects an ethernet interface it knows that a broadcastable medium is
    > >> connected. Broadcast is essential for ethernet.

    >
    > >> If router detects an serial interface it knows there is no broacastable medium.

    >
    > >> If your questions refers to configuration statement "ip ospf network broadcast"
    > >> have a look at this great documenthttp://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0...

    >
    > >> Especially pay attention on sections Neighbors and Adjacencies. It's all
    > >> explained herein very well.

    >
    > >> Andre- ?????????????? -

    >
    > >> - ?????????????? -

    >
    > >Thanks, I have checked the cisco url you list above.
    > >There is a command to assign network type "ip ospf network {broadcast
    > >| non-
    > >broadecast | point to multipoint}
    > >My question is if two routers connected via ethernet, Do I should use
    > >broadcast
    > >or non-broadcast or either way?
    > >/s

    >
    > it depends.
    >
    > some boxes (not cisco AFAIR) do not allow you to choose, as they limit
    > which options work on Ethernet.
    >
    > I have had major hassles with cisco to foundry links on GigE which
    > will not work with some permutations of the choices - but do not
    > bother to log why they do not form an adjacency......
    >
    > the "classic" argument is that point to point uses a bit less
    > resources in the router, so is "better" if you have a router with lots
    > of OSPF interface - but this needs more config.
    > Reality is if you are that close to the edge, your network is already
    > broken, but you havent provoked it enough yet......
    >
    > However - you imply this is "just point to point" - with many OSPF
    > devices actually being switches and sometimes using adjacencies on
    > VLANs, you can end up with more than 2 devices in a subnet even when
    > all the pysical connections are point to point.
    > Here, making a special case for when there are only 2 devices may make
    > life more complicated.
    >
    > personally - mimimum config and being consistent seems to cause fewer
    > problems so is the way to go. So - broadcast is my preferred setup.
    > --
    > Regards
    >
    > - replace xyz with ntl



    On a broadcast network, OSPF need to perform DR election.

    This not required on a point-to-point link when OSPF network type is
    configured as point-to-point and thus the OSPF adjacency should form
    more quickly.
     
    Merv, Sep 17, 2008
    #10
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