At 06:45 PM 1/21/2006, Guy Harris wrote:
Ulf Lamping wrote:
As you mention it, the wiki says: "Note that "dual-speed" hubs that
support both 10MBit and 100MBit ports might not send unicast traffic
between 10MBit and 100MBit ports; if so, you can only capture traffic
between hosts whose Ethernet interfaces are running at the same speed as
the Ethernet interface on the machine capturing traffic."
I've expanded that part of the HubReference page to give more detail,
describing the scenario I outlined in an earlier message.
The bridge between the two speeds seems to be a (bit of a) switch. I've
added your hub to the wiki and mentioned the bridge problems.
I'm assuming there are at least two types of dual-speed hubs - one type
with *no* bridge between the speeds, which I assume means that a 10Mb/s
host and a 100Mb/s host plugged into the hub can't communicate at all (so
there's no traffic between them to capture), and one type with a switch
between them (so that broadcast and multicast traffic are passed between
the speeds, and unicast traffic is passed to the port to which it's being
sent), which I assume means that a 10Mb/s host and a 100Mb/s host plugged
into the hub can communicate, but another host plugged into the hub can
only see one side of the conversation.
I can't imagine there would be a dual speed hub with no connection between
the 10 Mb and 100 Mb hubs. It doesn't seem to be useful behavior.
If each half really is a hub (all 10 Mb unicast traffic goes to all 10 Mb
ports), then I would think all unicast traffic that goes across the
internal switch would go to all ports - if it doesn't, then each half isn't
really a hub and shouldn't behave like one for traffic between ports.
(Are there any dual-speed hubs that pass *all* traffic? I could imagine a
lot of 100Mb/s traffic flooding a 10Mb/s port in that case.)
I wouldn't think so because most of the 100 Mb traffic would get dropped by
the 10 Mb hub due to flooding.
