Re: [PATCH nixpkgs] spectrumPackages: use link-local router addresses

["Cole Helbling" <cole.e.helbling@outlook.com>]

On Thu May 13, 2021 at 1:13 PM PDT, Alyssa Ross wrote:
> There's no need for every interface on a router to have it's own
> unique IP.  Using link-local addresses, we can assign every interface
> on a single router the same IP, and save the effort of
> adding/subtracting one all the time to infer the address of one side
> of a link from the other.
>
> This means that routers and clients are both only interested in what
> the IP of the client should be, since that's the only thing that is
> different between different links.  So we change our MAC format to
> communicate the client IP to both sides.  If we just made the whole
> NIC portion of the MAC the last three octets of an IP address like we
> did before, then both ends of the link would have the same MAC, so we
> still need to set a bit to encode whether a MAC is at the router side
> of the link or the client side.  I've decided to simplify the
> implementation by using the most significant bit of the NIC part for
> that, and just declaring the rest of that octet to be reserved.  This
> way, no calculation is required in the guests -- they just need to
> look at the last two octets.  And we can still identify 65536 links in
> this scheme, which should be enough for anybody, right?
> ---
> I'd like to move the networking to be IPv6.  That's a bit more
> complicated, but shouldn't get in the way of smaller improvements like
> this.
>
>  .../linux/spectrum/testhost/default.nix       | 25 ++++++++-----------
>  .../linux/spectrum/vm/app/default.nix         | 15 ++++-------
>  .../linux/spectrum/vm/net/default.nix         | 13 +++++-----
>  3 files changed, 23 insertions(+), 30 deletions(-)

Reviewed-by: Cole Helbling <cole.e.helbling@outlook.com>