uplink ports and best practice..autonegotiate or fixed speed

Discussion in 'Cisco' started by BrooklynBadass, Sep 12, 2007.

  1. I have new cisco switches...3560's and older 3coms superstack III and
    II connected via crossover cables.
    Can anyone advise on best practices for connecting the two? Should I
    fix the port speed? etc..
    thanks!
     
    BrooklynBadass, Sep 12, 2007
    #1
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  2. BrooklynBadass

    Trendkill Guest

    On Sep 12, 7:16 am, BrooklynBadass <> wrote:
    > I have new cisco switches...3560's and older 3coms superstack III and
    > II connected via crossover cables.
    > Can anyone advise on best practices for connecting the two? Should I
    > fix the port speed? etc..
    > thanks!


    Generally speaking (with the exception of gig for some vendors), you
    want to set to the same thing on both sides, whether that be auto/auto
    or 100full/100full, or whatever. Generally speaking, and while I do
    know of several devices where auto/auto is really required, most of
    the time it is best to hard code both sides and avoid auto-
    negotiation. Cisco has gotten a lot better with this in recent years,
    but you usually can't go wrong with hard-coding both to the setting
    you want, either 100/full or gig/full.

    Here is a link to the best practices:

    http://www.cisco.com/en/US/products...ech_note09186a00800a7af0.shtml#auto_neg_valid
     
    Trendkill, Sep 12, 2007
    #2
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  3. On Sep 12, 7:21 am, Trendkill <> wrote:
    > On Sep 12, 7:16 am, BrooklynBadass <> wrote:
    >
    > > I have new cisco switches...3560's and older 3coms superstack III and
    > > II connected via crossover cables.
    > > Can anyone advise on best practices for connecting the two? Should I
    > > fix the port speed? etc..
    > > thanks!

    >
    > Generally speaking (with the exception of gig for some vendors), you
    > want to set to the same thing on both sides, whether that be auto/auto
    > or 100full/100full, or whatever. Generally speaking, and while I do
    > know of several devices where auto/auto is really required, most of
    > the time it is best to hard code both sides and avoid auto-
    > negotiation. Cisco has gotten a lot better with this in recent years,
    > but you usually can't go wrong with hard-coding both to the setting
    > you want, either 100/full or gig/full.
    >
    > Here is a link to the best practices:
    >
    > http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_n...


    Thanks for the link and for the information. It looks as though either
    method will work and that manual configuration is prone to human
    error. I wonder what they mean by "the maturity of the technology has
    recently changed the view of autonegotiation.." as of when? The
    document was updated as of 8/2005 but what does that mean in terms of
    my 3com superstack 3 3300? My boss has made a big issue over a
    suggestion by a consultant regarding hard coding Speed & Duplex on
    Cisco switches connecting to 3com switches and is calling into
    question my work. Now I'm on the defensive and she wants me to email
    my config to a Cisco engineer. Note: We have no issue with
    performance.
    thanks for your input.


    FROM Cisco's website (link you provided)
    Recommended Port Configuration (Autonegotiation or Manual
    Configuration)
    There are many opinions on the subject of autonegotiation. Previously,
    many engineers advised customers not to use autonegotiation with any
    switch-connected device. However, improvements in the interoperation
    of autonegotiation and the maturity of the technology has recently
    changed the view of autonegotiation and its use. In addition,
    performance issues due to duplex mismatches, caused by the manual
    setting of speed and duplex on only one link partner, are more common.
    Because of these recent issues, the use of autonegotiation is regarded
    as a valid practice
     
    BrooklynBadass, Sep 12, 2007
    #3
  4. BrooklynBadass

    Trendkill Guest

    On Sep 12, 9:37 am, BrooklynBadass <> wrote:
    > On Sep 12, 7:21 am, Trendkill <> wrote:
    >
    >
    >
    > > On Sep 12, 7:16 am, BrooklynBadass <> wrote:

    >
    > > > I have new cisco switches...3560's and older 3coms superstack III and
    > > > II connected via crossover cables.
    > > > Can anyone advise on best practices for connecting the two? Should I
    > > > fix the port speed? etc..
    > > > thanks!

    >
    > > Generally speaking (with the exception of gig for some vendors), you
    > > want to set to the same thing on both sides, whether that be auto/auto
    > > or 100full/100full, or whatever. Generally speaking, and while I do
    > > know of several devices where auto/auto is really required, most of
    > > the time it is best to hard code both sides and avoid auto-
    > > negotiation. Cisco has gotten a lot better with this in recent years,
    > > but you usually can't go wrong with hard-coding both to the setting
    > > you want, either 100/full or gig/full.

    >
    > > Here is a link to the best practices:

    >
    > >http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_n...

    >
    > Thanks for the link and for the information. It looks as though either
    > method will work and that manual configuration is prone to human
    > error. I wonder what they mean by "the maturity of the technology has
    > recently changed the view of autonegotiation.." as of when? The
    > document was updated as of 8/2005 but what does that mean in terms of
    > my 3com superstack 3 3300? My boss has made a big issue over a
    > suggestion by a consultant regarding hard coding Speed & Duplex on
    > Cisco switches connecting to 3com switches and is calling into
    > question my work. Now I'm on the defensive and she wants me to email
    > my config to a Cisco engineer. Note: We have no issue with
    > performance.
    > thanks for your input.
    >
    > FROM Cisco's website (link you provided)
    > Recommended Port Configuration (Autonegotiation or Manual
    > Configuration)
    > There are many opinions on the subject of autonegotiation. Previously,
    > many engineers advised customers not to use autonegotiation with any
    > switch-connected device. However, improvements in the interoperation
    > of autonegotiation and the maturity of the technology has recently
    > changed the view of autonegotiation and its use. In addition,
    > performance issues due to duplex mismatches, caused by the manual
    > setting of speed and duplex on only one link partner, are more common.
    > Because of these recent issues, the use of autonegotiation is regarded
    > as a valid practice


    3com is the variable that I can't speak to. However, back in the day
    (I'd say late 90's/early 00's), leaving anything to auto on both sides
    frequently caused issues. For every box that worked fine, there was
    one with a NIC from a different vendor that re-acted differently and
    negotiated incorrectly. The same bet at this time was usually to hard
    code both sides to the speed/duplex you wanted. This is generally the
    same approach that most engineers I know take today just because of
    all of our prior experiences, but gigabit ethernet has pushed auto/
    auto as many cards do not have a 1000/full setting.

    Additionally, I agree w/ Cisco that things changed what seems to be a
    few years ago (2004/2005 is probably about right). I now have lots of
    boxes (probably a good 20%) that are auto on both sides and work
    great. In fact, some of our NIX boxes require it for some of their
    NICs depending on NIC function.

    To answer your question, I'm not sure what the 'best' is for your 3com
    equipment, but when in doubt, I always recommend hard-coding. I have
    had many more problems over the years with auto/auto than the few I
    have had when there was an issue with hard coding both sides. Just my
    2 cents.
     
    Trendkill, Sep 12, 2007
    #4
  5. BrooklynBadass

    Guest

    On 12 Sep, 18:10, Trendkill <> wrote:
    > On Sep 12, 9:37 am, BrooklynBadass <> wrote:
    >
    >
    >
    >
    >
    > > On Sep 12, 7:21 am, Trendkill <> wrote:

    >
    > > > On Sep 12, 7:16 am, BrooklynBadass <> wrote:

    >
    > > > > I have new cisco switches...3560's and older 3coms superstack III and
    > > > > II connected via crossover cables.
    > > > > Can anyone advise on best practices for connecting the two? Should I
    > > > > fix the port speed? etc..
    > > > > thanks!

    >
    > > > Generally speaking (with the exception of gig for some vendors), you
    > > > want to set to the same thing on both sides, whether that be auto/auto
    > > > or 100full/100full, or whatever. Generally speaking, and while I do
    > > > know of several devices where auto/auto is really required, most of
    > > > the time it is best to hard code both sides and avoid auto-
    > > > negotiation. Cisco has gotten a lot better with this in recent years,
    > > > but you usually can't go wrong with hard-coding both to the setting
    > > > you want, either 100/full or gig/full.

    >
    > > > Here is a link to the best practices:

    >
    > > >http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_n...

    >
    > > Thanks for the link and for the information. It looks as though either
    > > method will work and that manual configuration is prone to human
    > > error. I wonder what they mean by "the maturity of the technology has
    > > recently changed the view of autonegotiation.." as of when? The
    > > document was updated as of 8/2005 but what does that mean in terms of
    > > my 3com superstack 3 3300? My boss has made a big issue over a
    > > suggestion by a consultant regarding hard coding Speed & Duplex on
    > > Cisco switches connecting to 3com switches and is calling into
    > > question my work. Now I'm on the defensive and she wants me to email
    > > my config to a Cisco engineer. Note: We have no issue with
    > > performance.
    > > thanks for your input.

    >
    > > FROM Cisco's website (link you provided)
    > > Recommended Port Configuration (Autonegotiation or Manual
    > > Configuration)
    > > There are many opinions on the subject of autonegotiation. Previously,
    > > many engineers advised customers not to use autonegotiation with any
    > > switch-connected device. However, improvements in the interoperation
    > > of autonegotiation and the maturity of the technology has recently
    > > changed the view of autonegotiation and its use. In addition,
    > > performance issues due to duplex mismatches, caused by the manual
    > > setting of speed and duplex on only one link partner, are more common.
    > > Because of these recent issues, the use of autonegotiation is regarded
    > > as a valid practice

    >
    > 3com is the variable that I can't speak to. However, back in the day
    > (I'd say late 90's/early 00's), leaving anything to auto on both sides
    > frequently caused issues. For every box that worked fine, there was
    > one with a NIC from a different vendor that re-acted differently and
    > negotiated incorrectly. The same bet at this time was usually to hard
    > code both sides to the speed/duplex you wanted. This is generally the
    > same approach that most engineers I know take today just because of
    > all of our prior experiences, but gigabit ethernet has pushed auto/
    > auto as many cards do not have a 1000/full setting.
    >
    > Additionally, I agree w/ Cisco that things changed what seems to be a
    > few years ago (2004/2005 is probably about right). I now have lots of
    > boxes (probably a good 20%) that are auto on both sides and work
    > great. In fact, some of our NIX boxes require it for some of their
    > NICs depending on NIC function.
    >
    > To answer your question, I'm not sure what the 'best' is for your 3com
    > equipment, but when in doubt, I always recommend hard-coding. I have
    > had many more problems over the years with auto/auto than the few I
    > have had when there was an issue with hard coding both sides. Just my
    > 2 cents.- Hide quoted text -


    This is now a Religious issue mostly : -))

    May I recommend reading:-
    The Duplex Delusion - 2017 - Bod43 (Apologies to Richard Dawkins:)

    As discussed already just use whatever works. Many people hold
    very strong views on this subject however at the end of the
    day it is no big deal to figure out if you have a problem or not and
    to fix it.
    There is not and never has been a Right Answer to
    whether to use Auto or not.

    I recommend checking the interface counters
    once a bit of traffic has flowed and if there are no errors
    then all is OK. I have encountered devices that lied about their
    duplex setting so I like to check the interface counters.
    The cisco counters seem reasonably trustworthy.

    If you have a mismatch and are getting traffic that
    highlights the problem the HD end shows Late Collisions
    and the FD end CRC/Frame errors.

    I do know for sure that I have seen 100s of workstations with
    terrible performance due to poorly managed attempts
    to use manually set. I have also seen many poeple, while attempting
    to "fix" poor system performance, check the duplex setting
    of a port and if not FD set it to FD since it is 'obviously better'.
    Not even checking the oher end!!!

    Whatever you do make sure that both ends are the same : -)
     
    , Sep 12, 2007
    #5
  6. BrooklynBadass

    Guest

    At this point in time I believe setting things to auto is fairly safe.
    It really depends on how well that feature on the 3coms work.

    Performance will be identical If things negotiate properly with auto
    or are properly static.

    I've had issues with packet loss and weird network problems because
    things were set to 100full and not auto. Wait until you plug a
    workstation into one of those ports that is hard set in two years and
    can't figure out why you are getting strange packet loss. It's a
    problem that unless you have seen it recently you'll burn hours trying
    to figure out.

    My datacenter switches are all auto except to our uplink out of the
    gateway and things are fine.
     
    , Sep 13, 2007
    #6
  7. On Sep 12, 9:16 pm, "" <>
    wrote:
    > At this point in time I believe setting things to auto is fairly safe.
    > It really depends on how well that feature on the 3coms work.
    >
    > Performance will be identical If things negotiate properly with auto
    > or are properly static.
    >
    > I've had issues with packet loss and weird network problems because
    > things were set to 100full and not auto. Wait until you plug a
    > workstation into one of those ports that is hard set in two years and
    > can't figure out why you are getting strange packet loss. It's a
    > problem that unless you have seen it recently you'll burn hours trying
    > to figure out.
    >
    > My datacenter switches are all auto except to our uplink out of the
    > gateway and things are fine.


    Thanks for responding.
    The help I have received here over the years has been invaluable and I
    am grateful.
     
    BrooklynBadass, Sep 13, 2007
    #7
  8. BrooklynBadass

    Trendkill Guest

    On Sep 13, 5:21 am, BrooklynBadass <> wrote:
    > On Sep 12, 9:16 pm, "" <>
    > wrote:
    >
    > > At this point in time I believe setting things to auto is fairly safe.
    > > It really depends on how well that feature on the 3coms work.

    >
    > > Performance will be identical If things negotiate properly with auto
    > > or are properly static.

    >
    > > I've had issues with packet loss and weird network problems because
    > > things were set to 100full and not auto. Wait until you plug a
    > > workstation into one of those ports that is hard set in two years and
    > > can't figure out why you are getting strange packet loss. It's a
    > > problem that unless you have seen it recently you'll burn hours trying
    > > to figure out.

    >
    > > My datacenter switches are all auto except to our uplink out of the
    > > gateway and things are fine.

    >
    > Thanks for responding.
    > The help I have received here over the years has been invaluable and I
    > am grateful.


    While I don't disagree with any of the comments above, I will repeat
    that I have NEVER seen uplinks or trunks configured with auto/auto in
    any of the companies I have worked for (all Global Fortune 100), and
    in fact, I'm fairly certain that trunks cannot be auto but could be
    wrong there. In regards to other nodes, I do agree that both
    solutions are equally viable today and its really a case of trial/
    error or following documentation for specific vendors, but I would
    never leave backbone or distribution network links to negotiation.
     
    Trendkill, Sep 13, 2007
    #8
  9. BrooklynBadass

    MC Guest

    Trendkill wrote:
    > On Sep 13, 5:21 am, BrooklynBadass <> wrote:
    >> On Sep 12, 9:16 pm, "" <>
    >> wrote:
    >>
    >>> At this point in time I believe setting things to auto is fairly safe.
    >>> It really depends on how well that feature on the 3coms work.
    >>> Performance will be identical If things negotiate properly with auto
    >>> or are properly static.
    >>> I've had issues with packet loss and weird network problems because
    >>> things were set to 100full and not auto. Wait until you plug a
    >>> workstation into one of those ports that is hard set in two years and
    >>> can't figure out why you are getting strange packet loss. It's a
    >>> problem that unless you have seen it recently you'll burn hours trying
    >>> to figure out.
    >>> My datacenter switches are all auto except to our uplink out of the
    >>> gateway and things are fine.

    >> Thanks for responding.
    >> The help I have received here over the years has been invaluable and I
    >> am grateful.

    >
    > While I don't disagree with any of the comments above, I will repeat
    > that I have NEVER seen uplinks or trunks configured with auto/auto in
    > any of the companies I have worked for (all Global Fortune 100), and
    > in fact, I'm fairly certain that trunks cannot be auto but could be
    > wrong there. In regards to other nodes, I do agree that both
    > solutions are equally viable today and its really a case of trial/
    > error or following documentation for specific vendors, but I would
    > never leave backbone or distribution network links to negotiation.
    >

    I have in the past hard set when possible, on all switch ports used for
    servers and uplinks, we have any user workstations and servers on
    separate networks and switches so makes a lot easier.

    I have experienced many occasions when running auto on both ends and
    have heavy traffic from servers or on uplinks, I caused the ports to
    renegotiate and if there is still heavy traffic during that time can not
    negotiate correctly seems for the switch to negotiate requires
    additional processing that under heavy traffic loads gets interrupted or
    something.

    Server folks know to check their interfaces and set appropriately.
    I do use auto negotiation on copper gig ports for server connectivity
    but in many cases still hard set links between switches.

    I agree that the auto negotiation as gotten a lot better these days and
    in most cases is probably not needed to hard set.
    MC
     
    MC, Sep 13, 2007
    #9
  10. BrooklynBadass

    jas0n Guest

    > Server folks know to check their interfaces and set appropriately.
    > I do use auto negotiation on copper gig ports for server connectivity
    > but in many cases still hard set links between switches.
    >
    > I agree that the auto negotiation as gotten a lot better these days and
    > in most cases is probably not needed to hard set.
    > MC


    I'm seeing new 3750, sfp gig ports auto having problems with new hp
    dl360's where the server is pushed to 100 rather than 1000 ... setting
    it manually on the port and everything works at 1000. Haven't looked for
    a reason as yet, all cabling is new and its happened on a few new sites
    recently.
     
    jas0n, Sep 29, 2007
    #10
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