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Date:      Fri, 31 Jul 1998 13:51:24 +1000
From:      Richard Archer <rha@interdomain.net.au>
To:        freebsd-hardware@FreeBSD.ORG
Subject:   Support for passive backplane chassis?
Message-ID:  <l03130318b1e6eae3d5e0@[203.17.167.127]>

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Hello all!

I am working on setting up Internet access to an office building with
hundreds of ethernets. I want to isolate the individual ethernets as
much as possible, and running a FreeBSD system to as a router/firewall
seems to be a logical choice.

The number of ethernet segments involved means building the routers out
of normal four PCI slot motherboards would be unpleasant. Even with
quad-port ethernet cards (like the ZNYX NetBlaster ZX346) each router
would only be able to handle 15 segments. I'd finish up with 3 racks
full of PCs to maintain!

I am thinking of using a passive backplane system with 16 PCI slots.
This would allow each router to handle up to 64 ethernet segments.
But I can't find much information about how these interact with FreeBSD.

I am concerned that either the multiple PCI buses would not be detected,
or there would be lengthy delays introduced by transferring data across
the bridge. Is the fact that the multiple-port ethernet cards each
effectively contain a PCI-PCI bridge going to complicate matters?

I've searched the mailing list archives, but any discussion on this topic
dates back to 1996. Does anyone have experience with these devices they'd
care to share?

Also, the number of interrupts generated by 60 ethernet ports could get
quite high. Each ethernet segment only has a few computers, but 60
networks averaging 100 packets per second each will still generate
upwards of 6,000 int/sec. How many interrupts per second can FreeBSD
handle in this situation? Would this be affected by delays passing data
across the bridge?

Yours sincerely,
Richard Archer.



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