[nsp] ip load-sharing per-packet - cef accelerated ?

Tony Tauber ttauber at genuity.net
Mon Mar 10 19:41:09 EST 2003

On Mon, 10 Mar 2003, Jared Mauch wrote:

> On Mon, Mar 10, 2003 at 02:22:12PM -0800, Dan Hollis wrote:
> > My understanding is that 'ip load-sharing per-packet' is CEF
> > accelerated, yes?
> >
> > Just trying to understand why some providers won't support
> > per-packet CEF.
> 	A good reason they tend to avoid it is it causes out of order
> 	packets which result in lower end-to-end throughput.
> 	What you want is a srcIP/dstIP/srcPT/dstPT based balancing to
> 	be perfectly honest.  This will keep the same flows on the
> 	same circuit.
> 	- Jared

Jared's right, of course, though there could be cases where a given
flow could exceed the size of one of the parallel paths as in the case
of a proxy.

Here's something else to consider, though.  In the GSR architecture,
the outbound interface lookup is done on ingress.  Where the ingress
port is on an Engine 2 card (eg. Quad-OC12 or single-port OC48), there
does not exist the capability (so it's been explained to me by Cisco
engineers) to keep track of which interface a packet was last sent on
so that the per-packet decision could be implemented.

We've seen that MLPPP can work to distribute the load so that a given
flow can grow larger than the physical size of any of the component
parallel paths.  MLPPP isn't the CPU pig that it was in earlier
implementations or on different platforms.  Of course, YMMV.


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