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Managed switch that can limit autonegotiation to 10BASE-T full duplex

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  • 15-12-2016 3:57pm
    #1
    Tenshot
    Registered Users Posts: 648 ✭✭✭


    [ Edit: Not sure why original thread title was screwed up: what I entered was "Managed switch that can limit autonegotiation to 10BASE-T full duplex" ]

    The HP ProCurve 2510-24 managed switch lets you configure each port for auto-negotiation, while specifying options for speed and duplex. This is really useful, since you can set it to auto-negotiate 10BASE-T half-duplex or full-duplex, but NOT 100BASE-T -- ideal for a legacy network I manage which runs on CAT3 cabling.

    Anyone know of any affordable alternative vendors that support this level of configuration?

    All the other switches I've seen support either a single fixed speed or full auto-negotiation only. I could force 10BASE-T full-duplex, but this trips up clients who plug in devices set to auto-negotiate (i.e. all of them) -- their device defaults to 10BASE-T half-duplex and gets upset about collisions. Fixing the port speed at 10BASE-T half-duplex avoids this, but is about 20% slower than full-duplex on downloads.


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    #2
    Cuddlesworth
    Registered Users Posts: 13,983 ✭✭✭✭Cuddlesworth


    But if you set the switch to auto at 1 gig, in theory both sides should negotiate a acceptable connection at full duplex. Its when 1 side fixes a speed, then issues witrh duplex arise.

    What the HP's are doing are faking the capabilities of the switch port on layer 2 negotiation. That's at a base ASIC level on the procurve, I don't know any other vendors that do it and nobody else uses those provision ASICs.


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    #3
    Tenshot
    Registered Users Posts: 648 ✭✭✭Tenshot


    Cuddlesworth wrote: »
    But if you set the switch to auto at 1 gig, in theory both sides should negotiate a acceptable connection at full duplex. Its when 1 side fixes a speed, then issues with duplex arise.

    The problem is that autonegotiation for 10BASE-T and 100BASE-T happens at 10BASE-T speeds, and no quality checks are done on the cable itself - both speeds use a single Tx and single Rx pair. So, setting auto-negotiation at both ends will invariably train up the link at 100BASE-T, only for the link quality to be atrocious with near-100% data loss.

    Gigabit does qualify the cable quality and degrade gracefully to 100BASE-T when needed (even on four pairs) but that doesn't help here unfortunately.

    I've seen plenty of datasheets for Ethernet PHYs and the configuration registers usually have a configurable bitmask to indicate which modes and speeds are supported during auto-negotiation; it's just the system software on the switches that don't seem to bother exposing it :-(


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    #4
    Cuddlesworth
    Registered Users Posts: 13,983 ✭✭✭✭Cuddlesworth


    Tenshot wrote: »
    The problem is that autonegotiation for 10BASE-T and 100BASE-T happens at 10BASE-T speeds, and no quality checks are done on the cable itself - both speeds use a single Tx and single Rx pair. So, setting auto-negotiation at both ends will invariably train up the link at 100BASE-T, only for the link quality to be atrocious with near-100% data loss.

    Gigabit does qualify the cable quality and degrade gracefully to 100BASE-T when needed (even on four pairs) but that doesn't help here unfortunately.

    I've seen plenty of datasheets for Ethernet PHYs and the configuration registers usually have a configurable bitmask to indicate which modes and speeds are supported during auto-negotiation; it's just the system software on the switches that don't seem to bother exposing it :-(

    Never encountered this situation myself, but I was of the impression autonegotiation would do a integraty test and scale down to 10baseT

    Its such a specific use case, I think the real problem here is your cheap ass 2 decades old cabling.

    Consider buying second hand HPE equipment(1900 hundred series does it too) or Cisco switches. Or super old Hubs.


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    #5
    Tenshot
    Registered Users Posts: 648 ✭✭✭Tenshot


    Cuddlesworth wrote: »
    Its such a specific use case, I think the real problem here is your cheap ass 2 decades old cabling.
    You're not wrong! Problem is, the cost of recabling is prohibitive for this application.

    I've looked at other technologies like VDSL and HomePNA3 that would work okay over CAT3 but they all fall short on cost grounds. The current setup works out at about €10 per port, and just needs a standard CAT5 socket at the client end. Everything else I've looked at needs client-side equipment to turn it back into Ethernet and usually ends up being €100+/port when you factor everything in.

    Right now, the network is running on about eight 24-port Baystack switches, none of which is less than 13 years old - all purchased as surplus from eBay circa 2004-2006. We bought a few spares as well, but we've only had one outright failure since then, plus a couple of individual dead ports.
    Consider buying second hand HPE equipment(1900 hundred series does it too) or Cisco switches. Or super old Hubs.
    Hubs won't do it (half-duplex only, plus no VLAN support). I see several 1900-series HP switches on eBay at the moment for cheap money though so I'll try a few of those -- thanks!


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    #6
    Tenshot
    Registered Users Posts: 648 ✭✭✭Tenshot


    A belated update: this week, I finally found a modern switch that does what I need at a reasonable price.

    The Zyxel 24-port GS1900-24E gigabit managed switch is about €100 from Amazon, and lets you configure port speed and duplex independently. So, I can set 10BASE-T port speed, leave duplex on 'Auto' and it will correctly auto-negotiate 10BASE-T full duplex with clients set to auto-negotiate.

    As a cross-check, I also configured it for 10BASE-T Full Duplex. In this case, the switch remained at full duplex, but the far end reverted to 10BASE-T half-duplex, which is what I expected.

    (On a Windows machine, you can use the command powershell "Get-NetAdapter | select name, linkspeed, fullduplex" to see the current duplex setting for each network adapter.)

    The Zyxel's web interface is fine if a little cumbersome. It also has a (poorly documented) Telnet interface, internal PSU, is fanless, and can be rack-mounted (using the enclosed ears) or wall-mounted.

    So, it's perfect for my needs. I'm going to order a bunch of them now to replace all our 20-year-old switches.


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