Subject: RE: 169.254/16 IP addresses

From: Stuart Cheshire <[email-masked]>
Date: Mon, 8 May 2000 18:26:59 -0700

>Well, you've answered part of my question - do we have consensus that 
>169.254/16 addresses are *auto-configured link-local* addresses, and not 
>simply link-local addresses?

I think we can safely say that DHCP servers SHOULD NOT allocate 169.254 
addresses.

However, if the administrator configures the DHCP server to allocate 
these addresses, how much harm will it do?

You could make the argument that draft-cheshire-ipv4-linklocal-00.txt 
says that the algorithm for selecting a link-local address is 
implementation-dependent, and asking a DHCP server is a valid 
implementation-dependent way of selecting an address. If an address 
collision is detected, then the client will send a DECLINE to the DHCP 
server and then request a new address.

I agree that it would be pretty odd to configure a DHCP server to 
allocate 169.254 addresses instead of something else, like 192.168, but I 
don't see why it wouldn't work.

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer

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From: Ralph Droms <[email-masked]>
Date: Wed, 24 May 2000 01:05:02 -0400

>don't see why it wouldn't work.

169.254 and 192.168 addresses have slightly different properties: the
former are link-local while the latter are site-local.  I can't think
of a reason to manage link-local addresses with DHCP but perhaps
someone else can...

- Ralph

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From: "Bernard Aboba" <[email-masked]>
Date: Wed, 24 May 2000 16:47:42 -0700

>I can't think of a reason to manage link-local addresses with DHCP but
perhaps
>someone else can...

The major reason to consider this would be so as to allow hosts that can
only handle one IP address per interface to retain that address if and
when a DHCP server came up. This is only relevant in the case of small
networks, since one would presume that linklocal addressing is not going
to be used in enterprise networks.

However, if one is willing to allow a host to have more than one address
per interface (as Stuart has proposed) then you could get a new address
and keep the old linklocal one too.