8.1 xl + dual-speed Netgear hub = yoyo

Kevin Oberman kob6558 at gmail.com
Sat Oct 22 21:48:23 UTC 2011

On Oct 22, 2011 2:21 AM, <perryh at pluto.rain.com> wrote:
> Jeremy Chadwick <freebsd at jdc.parodius.com> wrote:
> > 1) I think you misunderstand what product it is you own.  You have
> > a hub, not a switch.  This is confirmed by the fact that auto-neg
> > chooses to negotiate half-duplex.  Instead, you went later and
> > messed about trying to force full-duplex, which isn't going to
> > work on a hub.  The fact you even tried it has many implications.
> Just one implication, really:  I tried "everything".  I know
> that some gear from this era did not autonegotiate speed/duplex
> correctly, so when the autonegotiated configuration didn't work
> I tried both explicit duplex settings at 100Mb.  (I don't _need_
> full-duplex, but tried it for completeness.)
> > If you want full-duplex, you need an actual switch.  Netgear
> > refers to "hubs" as actual hubs, and "switches" as actual
> > switches.  Do you know the difference?
> Yep, including the fact that a true hub can't do speed translation
> because it doesn't buffer the entire packet -- it retransmits each
> bit as received.  This device -- despite being called a hub -- has
> to contain at least one packet worth of buffering so that it can
> retransmit a packet received at one speed to the ports that are
> operating at the other speed.
> I also know, from direct experience with attempting to sniff traffic
> (via tcpdump, wireshark, etc.), that this model of so-called hub
> does _not_ unconditionally retransmit everything received from one
> port to all of the other ports, even if all are operating at the
> same speed.  It seems to be some kind of hub-switch hybrid.
> > This is the first time I have ever seen a hub in use in almost
> > 10 years.
> Most of the gear here is in the museum category.  The mail server
> is a Sun-3/60 that is over 20 years old.  It ain't broke.  (That's
> why there's a 10Mb hub, whose AUI uplink is connected to a 10Base-2
> transceiver.)  One of FreeBSD's advantages is that it tends to run
> well on old hardware.
> > 2) There is no guarantee your NIC is fully compatible
> > (negotiation-wise) with the hub.  Vendor interoperability problems
> > were extremely common "back in the day" (you're using a 3Com NIC
> > from the mid-to-late 90s ...
> Yep, see comment re #1.  However, if it were a negotiation problem,
> I would have expected hard-setting the NIC to 100 to have fixed it;
> the hub was showing that port as operating at 100.  (BTW this model
> of hub is about as old as the NIC.)
> > You can either replace the NIC with something else, or replace the
> > hub.  IMHO, I would replace both.
> I can replace the hub easily enough -- I have a 100-only Netgear
> that _is_ a true hub (has been used successfully for sniffing) --
> although I suppose being the same brand and about the same age it
> may have a similar compatibility problem :(
> Replacing the NIC is a bit more of a problem, because it's built
> onto the mainboard.  I do have some Intel NICs, and I _think_ the
> box has an unused slot.
> > 5) The xl(4) driver is extremely old and basically is not maintained
> > any longer.  I would not be surprised if this was a driver bug.
> It had occurred to me that there might be a driver problem -- that
> was one reason for posting -- although all I found with Google was a
> watchdog reset problem that was fixed long enough ago that the fix
> surely would have been in 8.1.  However if the driver is no longer
> maintained, and swapping out the hub doesn't fix it, it seems I may
> be reduced to playing musical NICs.

Wow. it's 1985 again. O remember those 10/100 hubs. They were a royal pain!

If I remember right, they kept costs down by building in half of a switch.
Traffic from a 10 port to a 100 port was buffered, but there was no
forwarding table and all packets were forwarded to all ports. Total crap!

I also remember that SOME hubs of that era had series problems if the cable
was too short.

You mentioned using a short cable. Have you tried a longer one? I seem to
recall that 3 meters was the minimum, but it was so long ago that my memory
is a bit fuzzy.

R. Kevin Oberman, Network Engineer
kob6558 at gmail.com

More information about the freebsd-stable mailing list