Software router state of the art

Kevin Oberman oberman at
Wed Jul 23 19:59:52 UTC 2008

> Date: Wed, 23 Jul 2008 14:17:53 -0400
> From: "William Herrin" <herrin-nanog at>
> On Wed, Jul 23, 2008 at 2:03 PM, Naveen Nathan <naveen at> wrote:
> >> The Endace DAG cards claim they can move 7 gbps over a PCI-X bus from
> >> the NIC to main DRAM. They claim a full 10gbps on a PCIE bus.
> >
> > I wonder, has anyone heard of this used for IDS? I've been looking at
> > building a commodity SNORT solution, and wondering if a powerful network
> > card will help, or would the bottleneck be in processing the packets and
> > overhead from the OS?
> The first bottleneck is the interrupts from the NIC. With a generic
> Intel NIC under Linux, you start to lose a non-trivial number of
> packets around 700mbps of "normal" traffic because it can't service
> the interrupts quickly enough.

Most modern high performance network cards support MSI (Message Signaled
Interrupts) which generate real interrupts only in an intelligent
basis. and only at a controlled rate. Windows, Solaris and FreeBSD have
support for MSI and I think Linux does, too. It requires both hardware
and software support.

With MSI, TSO, LRO, and PCI-E with hardware that supports these, 9.5
Gbps TCP flows between systems is possible with minimal tuning. That
puts the bottleneck back on the forwarding software in the CPU to do
the forwarding at high rates.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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