Subject: Is Link-Local address mandatory for a host device?

From: Prabhu Hariharan <[email-masked]>
Date: Wed, 10 Jun 2009 17:51:22 +0530

Hi,

For a end-device (a host), if the interface connecting to IPv6 network is
configured with IPv6 global address, then automatic configuration of
link-local address is mandatory for that interface?  Consider the host is
being statically configured with IPv6 default gateway address.

Without the presence of link-local address on interface, whether any
functionality or IPv6 conformance issue would arise?

So, for DAD it would use unspecified address (::) as source address, for
Address resolution it would use the IPv6 global address, no need of router
discovery / prefix discovery in this host and applications would use global
address.  In this case, presence of link-local address is necessary?

Thanks,
Prabhu H

---

From: Erik Nordmark <[email-masked]>
Date: Wed, 10 Jun 2009 10:38:40 -0700

Prabhu Hariharan wrote:
> Hi,
> 
> For a end-device (a host), if the interface connecting to IPv6 network 
> is configured with IPv6 global address, then automatic configuration of 
> link-local address is mandatory for that interface?  Consider the host 
> is being statically configured with IPv6 default gateway address.
> 

 From a conformance perspective I think the specs are clear that all 
IPv6 interfaces must be assigned a link-local address.

 From the practical perspective of "what would break" we have:

> Address resolution it would use the IPv6 global address, no need of 
> router discovery / prefix discovery in this host and applications would 
> use global address.  In this case, presence of link-local address is 
> necessary?

I suspect that you also can't use DHCPv6 for non-addresses (finding the 
DNS servers etc) since DHCPv6 might assume that some communication uses 
the link-local address. But I haven't checked in the RFC.

    Erik

---

From: "TJ" <[email-masked]>
Date: Wed, 10 Jun 2009 16:36:28 -0400

Possibly recalling incorrectly here, but I believe Vista can function sans
Link Local addressing.  
(IIRC - It tries, but doesn't care too much if it fails (due to DAD
collision, for example) ...)

/TJ

>-----Original Message-----
>From: [email-masked] [mailto:[email-masked]] On Behalf Of
Erik
>Nordmark
>Sent: Wednesday, June 10, 2009 1:39 PM
>To: Prabhu Hariharan
>Cc: [email-masked]
>Subject: Re: Is Link-Local address mandatory for a host device?
>
>Prabhu Hariharan wrote:
>> Hi,
>>
>> is configured with IPv6 global address, then automatic configuration
>> of link-local address is mandatory for that interface?  Consider the
>> host is being statically configured with IPv6 default gateway address.
>>
>> So, for DAD it would use unspecified address (::) as source address,
>> for Address resolution it would use the IPv6 global address, no need
>> of router discovery / prefix discovery in this host and applications
>> would use global address.  In this case, presence of link-local
>> address is necessary?
>
>I suspect that you also can't use DHCPv6 for non-addresses (finding the DNS
>servers etc) since DHCPv6 might assume that some communication uses the
link-
>local address. But I haven't checked in the RFC.
>
>    Erik
>
>
>--------------------------------------------------------------------
>IETF IPv6 working group mailing list
>[email-masked]
>Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
>--------------------------------------------------------------------

---

From: Francis Dupont <[email-masked]>
Date: Thu, 11 Jun 2009 00:21:14 +0200

In your previous mail you wrote:

=> as far as I know at the exception of some very specific link types
the configuration of a link-local address per link is mandatory
(note I didn't add "automatic"). BTW a default gateway address is
supposed to be link-local.

=> some packets on the link are required to use a link-local address.

=> DAD is per address (cf the DAD vs DIID debate).

Regards

[email-masked]

---

From: "Hemant Singh (shemant)" <[email-masked]>
Date: Wed, 10 Jun 2009 22:14:53 -0400

>the link-local address. But I haven't checked in the RFC.

Snipped from RFC 3315, section 1.1 is:

[Clients and servers exchange DHCP messages using UDP [15].  The
 client uses a link-local address or addresses determined through
 other mechanisms for transmitting and receiving DHCP messages.]

Using link-local for DHCPv6 has the advantage that well-known mcast
addresses can be used for clients to communicate with the server or
relay agents.  RFC 3315 also mentions such an advantage in section 3. Of
course, even IPv6 mcast uses link-local address.  So really, it is not
wise for a host to not use a link-local address at all. 

Hemant

---

From: Behcet Sarikaya <[email-masked]>
Date: Thu, 11 Jun 2009 12:33:48 -0700 (PDT)

Folks,
  MLD also requires link-local IPv6 source addresses, RFC 3810, Sec. 5:

All MLDv2 messages
   described in this document MUST be sent with a link-local IPv6 Source Address, an IPv6 Hop Limit of 1, and an IPv6 Router Alert option
   [RFC2711] in a Hop-by-Hop Options header..  

So no escape from the link-locals.

Regards,

Behcet

----- Original Message ----
From: Hemant Singh (shemant) <[email-masked]>
To: Erik Nordmark <[email-masked]>; Prabhu Hariharan <[email-masked]>
Cc: [email-masked]
Sent: Wednesday, June 10, 2009 9:14:53 PM
Subject: RE: Is Link-Local address mandatory for a host device?

Hemant

---

From: Prabhu Hariharan <[email-masked]>
Date: Fri, 12 Jun 2009 09:40:57 +0530

Thanks all for the replies.

-- Prabhu H

On Fri, Jun 12, 2009 at 1:03 AM, Behcet Sarikaya
<[email-masked]>wrote:

>    described in this document MUST be sent with a link-local IPv6 Source
> Address, an IPv6 Hop Limit of 1, and an IPv6 Router Alert option