Subject: Re: [dhcwg] ARP reply vs. ARP request to announce address acquired from DHCP

From: Ted Lemon <[email-masked]>
Date: Mon, 13 Jan 2003 21:27:46 -0600

The thing that is missing on the Unix side is not the ability to *send* 
an ARP packet, but the ability to see the reply.   It didn't work when 
I looked at it ~five years ago, and I haven't bothered since.

I'll bet that when dhcpcd configures the interface, it generates the 
ARP request anyway, even though dhcpcd is sending an ARP reply.

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From: Ted Lemon <[email-masked]>
Date: Mon, 13 Jan 2003 23:23:12 -0600

> I can't think of any packet capturing facility that would not let
> you see ARP. dhcp-agent happily ARPs. In -current you can find
> the code in dhcp-arp-discovery.c

BPF wasn't passing arp-reply packets at the time.   Perhaps it does 
now, or perhaps it's handled differently in lpf.   I thought it was 
rather odd at the time, but at the time fixing it wasn't my main 
priority, so I didn't look any further.

> I can test against BSD and Solaris too but serial conning them is
> too much of a pain right now :-) Were you using a windows box to
> with your earlier test?

BSD definitely sends the ARP - I've captured it in packet traces when 
debugging.   Dunno for sure about Solaris, but it uses the BSD stack, 
so it probably does.   Linux doesn't use the BSD stack, which perhaps 
explains the discrepancy - it could be that Stevens was reporting what 
the BSD stack was already doing, rather than recommending what it 
*should* do.

So the question is, what does this tell us?   Are you saying that 
Stuart's proposal is not the right way to go, or just pointing out new 
information?   I have to say that I find Stuart's rationale for sending 
an ARP request rather than a reply fairly convincing.

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From: Ted Lemon <[email-masked]>
Date: Tue, 14 Jan 2003 00:03:18 -0600

> No need to update the RFC for this. Just send an ARP reply from
> the client and let the OS send all the requests it wants :-)

That's a fine engineering solution, but it's a lousy protocol solution 
- we can't specify two broadcasts.   A better way to phrase my question 
would be, "are you objecting to what is specified in Stuart's draft?"