[e2e] Question about fast path / slow path and IPv6

Sam Manthorpe sm at mirapoint.com
Sun Aug 31 03:16:08 PDT 2003

Is there really any significant difference between slow and fast
paths these days?  Do people still implement 'fast' path and is it
still considered worthwile to do so?  i.e. my desktop's slow path
will take on your fast path:-)   Seems to me that the silicon start-up
companies tried to take refuge in TCP a few years ago and that
just didn't pan out.

> > > Is IP fast path / slow path processing (for packets carrying
> > > IP options) similar for IPv4 and IPv6 in most current routers?

I don't know about router companies, but if you are routing
through any IPv6 version of IRIX on an SGI machine the
overhead is identical for v4 or v6, and if you have
one of the more expensive varieties the machine
will be able to achieve throughputs in the order of
10GB/s linespeed, using the obligatory slow path.

-- Sam

> >
> > The answer depends *entirely* on which hardware one is talking about.  > >
> > Some products can handle IP packets (with or without options)
> > at wire speed (usually because this is done in hardware).
> >
> > Other products cannot do so -- in which case only packets without
> > options are "fast path" and packets with options are "slow path".
> > This last case includes all (or nearly all) routers that use
> > CPU-based packet forwarding.
> >
> > "Most" could mean the the largest-volume deployments of a single
> > router model, in which case ask your nearest vendor C salesperson
> > what they do.  I'm assuming "most" means "most vendors" in the
> > quoted text above.
> >
> > Ran
> > rja at extremenetworks.com

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