There are four-port (actually 5-port) switches on PCI cards out there.
These cards provide 10/100/1000 switching between all five ports, but one of
the ports is wired internally to the PCI bus and makes the device look like
a regular Ethernet card.
I have no idea if any such card would work in a Soekris system. I just know
they're out there.
The only advantage of using such a card with a Soekris, however, is that you
could get one with all five interfaces running at 1Gbps. As has been
discussed on this list previously, that might not actually be a good thing.
The cheaper and probably better solution would be to get an inexpensive
five-port GigE switch and connect the first port to the Soekris.
Chris -)-----
der Mouse wrote:
>>> the ports are just ethernet interfaces so all your switching is
>>> being done in software if that's what you're asking.
>> Would that mean that a pair of machines transferring at full speed on
>> eth0 and eth1 would not reduce the available bandwidth for another
>> pair on eth2 and eth3?
>
> Depends on multiple factors.
>
> - Ethernet hardware. Sometimes there's a shared piece of hardware that
> can't handle full-bore I/O on all ports at once - I don't know
> whether this is true of the 5501 or not.
>
> - Bus bandwidth (this is, strictly, a shared piece of hardware such as
> mentioned above, but it's shared with, typically, a lot more than
> just the Ethernets). However, when doing a software switch, packet
> contents must be copied across the bus into main memory, then copied
> back again on transmission. Depending on the bus(es) involved and
> how DMA works, this may or may not be a problem.
>
> - CPU. The CPU has to look at each packet at least a little (typically
> just the Ethernet header, but that means servicing a cache miss, and
> probably some kind of shootdown when the DMA happened too).
>
> - Likely other factors I haven't though of.
>
> My guess - and it's a total guess - would be that bus bandwidth will be
> your limiting factor. But I'd have to measure it to be sure. If the
> other factors are capable enough, the limiting factor will be the
> network wire speed; this is the best case from your point of view, and
> for all I know might actually obtain for you.
>
>> If not, then how can that be achieved.
>
> Dedicated switches typically have custom silicon for the switching
> fabric. If you want full wire speed on a lot of fast ports at once
> ("fast" may include 100Mb and almost certainly includes Gb), you won't
> get it without custom silicon. But if your "full speed" is slow
> enough, you will be able to do OK with a software switch (but "slow
> enough" depends on the other factors).
>
> One thing you will _not_ get with a software switch is cut-through
> switching, packet forwarding where transmission starts as soon as
> enough of the Ethernet header is received to tell where the packet
> should go (if the destination channel can handle a send at the moment).
> Each packet must be fully received by the hardware before forwarding
> decisions are made. This does not, strictly speaking, impair
> bandwidth, but it does mean forwarding latency will be higher than with
> custom dedicated silicon switching hardware, which for some kinds of
> workloads is operationally similar to bandwidth limits.
>
> In short, it's a complex question. About all that someone not working
> closely with your situation can say with confidence is "it depends,
> you'd have to try it to be sure".
>
> /~\ The ASCII Mouse
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--
"Implementing CIFS - the Common Internet FileSystem" ISBN: 013047116X
Samba Team -- http://www.samba.org/ -)----- Christopher R. Hertel
jCIFS Team -- http://jcifs.samba.org/ -)----- ubiqx development, uninq.
ubiqx Team -- http://www.ubiqx.org/ -)----- [email protected]
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