[ECOS] Temporary IP address assignment trick

[Jonathan Larmour]

Grant Edwards wrote:
> I've noticed that a couple embedded devices I've played with
> allow you to assign an IP address temporarily using an arp
> trick...
> 
> If the device starts up with no IP address, and it subsequently
> receives an Ethernet frame with its MAC address, the IP stack
> will adopt the IP address in that frame as its own.  Typically
> one then points a telnet client or web browser at the device
> and configures its IP address permanently.
[snip]
> This is a very handy way to get a brand-new-out-of-the-box
> embedded device up and running without requiring a DHCP server.
> 
> How hard would it be to get either of the eCos stacks to behave
> like that?

This looks very similar to Reverse ARP, or RARP: 
<http://www.networksorcery.com/enp/rfc/rfc903.txt>. This technique is 
older than BOOTP I believe. Looking at the man page for rarpd, I see it 
has a -A option that's probably what you're seeing.

RARP servers certainly exist and are used, although it'd probably be 
better to implement "real" RARP (for all it is) if anything, then a 
kludged ARP, although we could do the latter as an option of course.

As for getting the stacks to do it - I'd have thought it would be pretty 
simple - you only need to change init_all_network_interfaces.

One slightly annoying thing with the stack is that it "pretends" it got a 
DHCP/BOOTP address even if it's statically defined - sticking stuff in the 
global eth0_bootp_data structure (bad namespacing, no biscuit). The same 
would unfortunately have to happen for RARP.

Jifl
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