FBSD 1GBit router?

[Erik Trulsson]

On Sun, Mar 02, 2008 at 04:11:28PM +0100, Ingo Flaschberger wrote:
> Dear Bareney,
> 
>>> And back to 1x is not fast enough:
>>> There are no 1gbit single port network cards that
>>> support more than 1
>>> lane, even if you plug it into a 16 lane slot.
>>> (and I'm not talking about 10gbit cards; if you have
>>> 10gbit upstream you
>>> have enough $$ to buy good gear)
>> 
>> Ok, well I've never seen a router with 1 port.  I
>> thought we were talking about building a router?
> 
> Have you ever read the link?
> Have you noticed that the axiomtek appliance has 7 gigabit ports?
> Each one connected with 1 lane pci-e?
> 
>> The lack of PCIe cards is a good reason to consider a
>> PCIX machine. On the systems that we have, the 1x PCIe
>> ports are a lot slower than a PCI-X card in the slot.
> 
> Perhaps, but: pci-x: 4gbit for the whole bus system.

PCI-X actually has up to twice that:
133 MHz * 64 bits = 8.512 Gbit/s ( = 1.066 GB/s )

That's assuming only a single PCI-X device on the bus.
If you have two devices connected to the same PCI-X bus
then most motherboards will lower the clock frequency
to 100MHz for reliability reasons. If there are 3 or more
devices connected to the same PCI-X bus then the clock frequency
is usually lowered to 66 MHz.
(Yes, the more devices you connect to a PCI-X bus, the less bandwidth
you get to share among them.)


> pci-e: 2gbit/lane

In each direction. The total bandwidth available is 4Gbit/s per lane.
(This is similar to Gigabit ethernet which can only send 1Gbit/s in
each direction, but can send and receive at the same time, thus using
a total bandwidth of up to 2Gbit/s.)


> 
>> You need 4Gb/s of throughput to handle a gigablt
>> router. (1 GB/s full duplex times 2).  1x is 4Gb/s
>> maximum. In my view, you always need twice the
>> bandwidth on the bus to avoid contention issues.
> 
> sample1:
> 3 pci-cards:
> card 1: 1x = 2gbit (dedicated)
> card 2: 1x = 2gbit (dedicated)
> card 3: 1x = 2gbit (dedicated)
> --------------------
> sum:         6gbit
> (but the use only 3)
> 
> sample2:
> 2 pci-x cards
> card 1: 4gbit (shared)
> card 2: 4gbit (shared)
> card 3: 4gbit (shared)
> ---------------------
> sum:    4gbit
> 
> homework:
> calculate with 7 ports.
> 
> Kind regards,
> 	Ingo Flaschberger
> 
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-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at student.uu.se