Re: Broadcast ARP packets on link local addresses (Version2).

["Janos Farkas" <chexum+dev@gmail.com>]

On 4/6/06, David Daney <ddaney@avtrex.com> wrote:
> Janos Farkas wrote:
> > Shouldn't it
> > be more correct to not depend on the ip address of the used network,
> > but to use the "scope" parameter of the given address?

> RFC 3927 specifies the Ethernet arp broadcast behavior for only
> 169.254.0.0/16.  Presumably you could set the scope parameter to local
> for addresses outside of that range or even for protocols other than
> Ethernet.  Since broadcasting ARP packets usually adversely effects
> usable network bandwidth, we should probably only do it where it is
> absolutely required.  The overhead of testing the value required by the
> RFC is quite low (3 machine instructions on i686 is the size of the
> entire patch), so using some proxy like the scope parameter would not
> even be a performance win.

Indeed, I just have a bad feeling about hardwiring IP addresses this deep.

The problems with "my" idea would be, summarily, after a day:

Q: Is there are reason to use broadcast ARP semantics for other IP
address ranges?
A: Maybe, but no RFC defines that.
Q: Is there are reason to NOT use broadcast ARP semantics for the
defined IP address ranges?
A: Maybe, but the RFC is against it.
Q: Is there a reason to expect people (and tools) to use/define scopes?
A: Probably, but it's still uncommon practice :)  I mean, how many of
us have 192.168.x.x addresses with "global" scope? I know I do.

I'm still in a losing position :)

Janos