RE: [RRG] Six/One Router: Provider-Independence, IPv4/IPv6 Interworking, Backwards-Compatibility

[Randall Atkinson <rja@extremenetworks.com>]

% Would be interesting to find out how prevalent routers with slow-path
% processing of IPv4 header options are in the DFZ.

Nearly all IPv4 routers of all types shunt any packet containing
any IPv4 option via CPU-based slow-path forwarding.  I do not
myself know of even 1 exception to this.  DFZ routers would
not generally be an exception to this.

In most cases, what happens is a header length check -- if the header
length is anything other than minimal legal IPv4 header size then
the packet goes to the CPU and leaves the hardware (or software)
fast path forwarding.

% IPv6 Destination Options headers that are not used
% for source routing are not looked at by routers.

s/are not looked/should not be looked/

One might want to run the experiment with some real routers
to verify the actual behaviour.

Ours ought not look at stuff inside an IPv6 Destination Option,
but I haven't verified this experimentally or by looking at
source code (I am in research, and am not working on products.)

I have no real idea either way what other implementations
might have done in this area.

Cheers,

Ran


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