Subject: RE: Suitability of v4LL in a managed network [was Application software needs to be "zeroconf-aware"?]

From: "Christian Huitema" <[email-masked]>
Date: Sat, 11 Jan 2003 11:45:01 -0800

>         "Networks where ZEROCONF protocols apply can include (but are not
> limited to) environments where no DHCP, MADCAP or DNS servers are
> present."
> [http://www.ietf.org/html.charters/zeroconf-charter.html]
>
> The "but are not limited to" phrase, I think, allows for v4LL to
> coexist with DHCP.

Another read on the same phrase is that the charter certainly does not mandate that IPv4 autoconfiguration be available when DHCP, MADCAP or DNS servers are present. I believe the IPv4 address autoconfiguration design should follow the general robustness principle, "be conservative in what you send, liberal in what you accept." The way I read this principle is that nodes on a DHCP managed network generally do not gain much functionality by getting a second IP address for the same interface, and that they may in fact loose some functionality as having multiple addresses of different scopes wil confuse some existing application. The conservative solution would thus be to not use autoconfigured addresses when a DHCP assigned address is present, which translate in the requirement that no IETF standard should ever require the specific use of the autoconfigured addresses. The liberal part of the statement would be to accept traffic from autoconfigured addresses even if the host does not actually use these addresses, e.g. accept incoming TCP connections.
 
-- Christian Huitema

---

From: Vincent Lubet <[email-masked]>
Date: Sat, 11 Jan 2003 16:22:18 -0800

On Saturday, January 11, 2003, at 11:45  AM, Christian Huitema wrote:

> Another read on the same phrase is that the charter certainly does not 
> mandate that IPv4 autoconfiguration be available when DHCP, MADCAP or 
> DNS servers are present. I believe the IPv4 address autoconfiguration 
> design should follow the general robustness principle, "be 
> conservative in what you send, liberal in what you accept." The way I 
> read this principle is that nodes on a DHCP managed network generally 
> do not gain much functionality by getting a second IP address for the 
> same interface, and that they may in fact loose some functionality as 
> having multiple addresses of different scopes wil confuse some 
> existing application. The conservative solution would thus be to not 
> use autoconfigured addresses when a DHCP assigned address is present, 
> which translate in the requirement that no IETF standard should ever 
> require the specific use of the autoconfigured addresses.

I agree it's very reasonable not to require an LL address to be 
assigned when a non LL address is assigned to a network interface.

> The liberal part of the statement would be to accept traffic from 
> autoconfigured addresses even if the host does not actually use these 
> addresses, e.g. accept incoming TCP connections.

This is really needed because using autoconfigured LL addresses is the 
only way to access some devices that have not been yet configured.

Vincent

---

From: Brad Hards <[email-masked]>
Date: Sun, 12 Jan 2003 15:16:34 +1100

> assigned when a non LL address is assigned to a network interface.
http://www.zeroconf.org/w3onwire-zeroconf.pdf contains a good intro to why 
this is needed. 

Brad
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