Need Ethernet Hub - NOT Switch

can you go in and set the cache so small it will always overflow? According to another thread here, most switches become hubs when the cache fills up....

CDP would only be filtered by Cisco switches, wouldn't it? I believe the DST of a CDP frame is 01:00:0C:CC:CC:CC, and that this should be treated as a regular MC frame by devices not implementing the proprietary CDP.

What he needs is an _old_ hub, made when it was still expensive to make a switch.

might be a good bet. 100TX only though, not dual-speed, if that's a problem.

Somebody needs to make a list of "real" vs "imitation" hubs.

On 16.03.2005 04:15 sqrfolkdnc wrote

Note: but only for the "excess" traffic. I.e. for traffic to MAC destinations not in the cam table (cache).

I would have a look at eBay where you can get relative new 24-port hubs for small money (

In article , Petri Krohn wrote: :"Ken Mandelberg" kirjoitti viestissä :news:d17tro$ snipped-for-privacy@mathsunf.mathcs.emory.edu...

:> I'm looking for a simple unmanaged 16 port rack mountable 100mbit :> ethernet hub, which is NOT a switch.

:WHY would you want to use a hub, not a switch?

:I can imagine you could use a small hub to monitor traffic, maybe in some :lab or test environment, but why 16 ports and a fixed installation?

Perhaps he needs to monitor a number of devices.

Perhaps (considering his university email address) he needs it for teaching purposes, so a number of students can all get copies of the packets.

Perhaps he needs to connect devices that have difficulty with autonegotiation .

Perhaps he needs to connect a number of devices that need layer 2 frames that are not passed through switches, such as CDP (Cisco Discovery Protocol) or Cisco PIX LAN failover keep-alives.

If you buy a used box made by Cisco/3Com/HP you can trust that if it says it's a hub, it's a hub.

before buying you should get the model # and grap the manual from the manufacturer's web site and read up to make sure you know what youi are buying. I wouldn't trust a seller to describe the item correctly.

HP has a lifetime warranty on some of it's gear. Hard to go wrong.

Right idea, but I beleive that it's a bridge that connects the two sides and I expect that the chip used is much faster than the 10Mb side can either source or sink bits and so it's effectivly invisible. A basic bridge passes all traffic.

I believe the HP Procurve line has a lifetime warranty. If you're worring about warranty coverage buy two or three on ebay and keep them for spares. I see Cisco 24 port 10/100 hubs are going for as little as $40 on ebay.

"Ken Mandelberg" kirjoitti viestissä news:d17tro$ snipped-for-privacy@mathsunf.mathcs.emory.edu...

WHY would you want to use a hub, not a switch?

I can imagine you could use a small hub to monitor traffic, maybe in some lab or test environment, but why 16 ports and a fixed installation?

A dual speed hub used to be two repeaters linked by a single bridge.

I mentioned that mainly to save clicking the link if he needs 10baseT.

No offence meant, but surely there can be no such thing, literally, as a "dual-speed hub"? There are/were some boxes which contain, in effect, a 10M hub and a 100M hub, interconnected by a switch. They used to be marketed as "dual speed hubs", but technically we knew what that really meant.

Thanks for all the responses.

As to why we don't want a switch:

We already have a large rack mounted mesh of switches. The hub was to consoldiate a collection of wireless access points onto one of the switch ports. Because of mobility issues we didn't want to deal with any issue of the switch having to relearn port association when a wireless session flipped between access points. It would also be a plus to be able to monitor from any of the hub ports.

We used the Linksys EF2H16 "hub" for a while thinking it was as advertised not a switch. Mostly it worked fine, even when laptops moved between access points. However, sometimes it didn't. In some cases we saw a laptop able to broadcast its dhcp request all the way through to the dhcp server, but unable to get its unicast reply. The "hub" was confused about what port to send the reply to, and this persisted for hours.

That example might just indicate a poor Linksys implementation, or even a defective piece of hardware. I was really only expecting a few second of trouble on port switching. Still it seems to me a real hub is what we want. If we wanted a switch we could connect directly to ports on our managed switches and not need a hub at all.

Ebay references:

Thanks also for the ebay pointers on older hubs. I might go this way, though my preference would be to get a new/warranteed piece of hardware if such a thing exists.

Only Cisco and (some) HP switches eat cdp frames. Other switches happily pass it along.

Ken, at the risk of stating the obvious, you're at a University, can you not just email your networking colleagues explaining your problem and asking if anybody can swap a hub for a switch? I have two 16 port hubs sitting in a cupboard, surely there must be loads in Emory.

And if you can't get a 16-port hub you should be able to daisy-chain two 8-porters together.

John

"Ken Mandelberg" kirjoitti viestissä news:d17tro$ snipped-for-privacy@mathsunf.mathcs.emory.edu...

There is right now on eBay two 3C250's for $19.95 (for both), plus $39.95 shipping. The shipping is a little high, but they are a little heavy. Those are real 100baseTX 24 port rack-mountrepeaters, maybe even class I.

-- glen

As far as I know, they are all hubs, some repeaters and some bridge/switch (two different words for the same thing).

Since the original hubs were repeaters, they got associated with the word hub, but hub is supposed to describe the wiring topology, not the electrical characteristics of the box. (There are also coaxial repeaters and AUI repeaters, neither of which are usually called hubs.)

-- glen

Your switch is configurable? Can't you configure all ports into promiscuous mode?