Subject: RE: Should people still be making IPv4 products?

From: "Christian Huitema" <[email-masked]>
Date: Sat, 28 Dec 2002 22:26:14 -0800

>> The other issue is the nature of these addresses, and specifically
>> whether they should be used "in addition to" other IPv4 addresses. I
>> think they should not, as adding this "link local" concept to IPv4 is
>> effectively a change in the IPv4 architecture, which is way outside
>> the charter of the working group
>
> IPv4 already allows interfaces to have multiple IP addresses.   IPv4
> link-local addresses already work, and have worked for quite some time,
> and are deployed on the vast majority of all deployed devices that run
> TCP/IP.   
 
Actually, the Windows implementations will not use autoconfigured IPv4 addresses if they already have obtained a DHCP address. Saying that "IPv4 link local already work" is a bit of an overstatement; what works is autoconfigured addresses on a disconnected network. Anything else is speculative. For example, one may speculate on the consequences of using autoconfigured addresses in a large entreprise network.
 
-- Christian Huitema

---

From: "John C. Welch" <[email-masked]>
Date: Sun, 29 Dec 2002 02:03:28 -0500

On 12/29/2002 01:26, "Christian Huitema" <[email-masked]>
wrote:

> Actually, the Windows implementations will not use autoconfigured IPv4
> addresses if they already have obtained a DHCP address. Saying that "IPv4 link
> local already work" is a bit of an overstatement; what works is autoconfigured
> addresses on a disconnected network. Anything else is speculative. For
> example, one may speculate on the consequences of using autoconfigured
> addresses in a large entreprise network.

Um...well, experience suggests that as long as the interface has both an LL
address and an address set up for the enterprise network, and the device can
handle multiple IPs per interface correctly, then the consequences should be
minor. If there are no other nodes with LL addresses on the local link, then
the LL configured address will just kind of sit there. The use of enterprise
addresses should never notice this other config unless that Enterprise is
using the LL subnet for its own addresses. In that case, the LL address
surrender mechanism should function and the LL interface will just find a
different address. Unless you have the full /16 number of devices on that
physical link, (and if you have 60,000+ devices on a flat subnet, you have
other issues anyway) then at most, DHCP will take an extra few milliseconds
to assign you an address.

 If you look at it, we already *have* autoconfiguration of addresses in
DHCP, which has almost no effective security. But it works. All LL is doing
is removing the server, and specifying the subnet for the address range. I
have yet to see concrete evidence that this is going to cause an existing
network to suddenly collapse in a storm of address errors.

john

-- 
John C. Welch
Consultant III
Administrative Computing
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