On 10/13/06, Dave Camp wrote:
> - Add a static entry to the ARP table for x.x.x.x -> Printer MAC
>Address, where x.x.x.x is the new IP address they want to set the
>printer to and the Printer MAC address is the MAC address of the
>printer.
> - Send an ICMP ping to the printer.
> - Remove the ARP entry
>
>Yes, they set the IP address of the printer by pinging it. I'll wait
>here for a bit while you cry.
>
>I'm going to guess that fiddling with the local ARP table is probably
>not such a swell idea
It turns out DHCP Servers do this all the time. The client broadcasts a
request saying can someone configure me, and the DHCP server responds
saying here's a configuration. In order to send the configuration to
the requesting client, it stuffs the clients hardware address into the
ARP cache and then does a UDP send to the corresponding IP address
[IPNetRouter did this on Mac OS 9]. The technique they're using is not
uncommon.
The easy way to do this on Mac OS X is to invoke the UNIX arp command to
do it for you. It's not as if you will be responding to dozens of
requests per second.
Alternatively, if you really want to send a raw Ethernet frame, you can
do something like "bpftransmit" in the Darwin "bootp" project. You'll
need a privileged helper tool to open a BPF socket, but it's not too bad
once you get the pattern (see Quinn's MoreAuthorization" sample code).
[IPNetRouterX does this.]
> and that I'd be better off hand rolling my own
>raw ICMP ping packet at the ethernet level to get the job done. I
>think it would have to be at the ethernet level as I need to specify
>the IP address and destination MAC address myself. I know I will have
>to have a SUID root helper tool to do this.
>
>Assuming that is the case, I was wondering if someone could point me
>to some sample code illustrating how to build a raw ethernet packet.
>I've looked in the Unix Programming Book, but it only covers raw
>IPv4/6 packets, not raw ethernet packets. Most of the sample code
>I've found on the net is for Linux which appears to use different AF_
>and protocol constants than BSD.
>
>Thoughts?
If you have any influence on future device firmware, there's open source
sample code for doing Bonjour, and a basic DHCP client is not that hard
in the scale of everything else the device is doing that requires a
multitasking OS and TCP/IP stack. [I've written both a DHCP Server and
DHCP Tester (client simulator) for my own products.]
Enjoy!
- Peter Sichel
Sustainable Softworks
www.sustworks.com
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