Subject: [Softwires] Provisioning Format for CPE BR/lwAFTR Address

From: <[email-masked]>
Date: Fri, 26 Apr 2013 10:15:06 +0200

Hi,

Sorry to dig this one up again, but although there has been a fair bit of discussion around the topic, I don't think that we have so far reached an agreement on how to provision sw CPEs with the address of the concentrator for MAP-E and lw4o6. We need to get a final answer on this as there's a few drafts (softwire-unified-cpe, softwire-map-dhcp, softwire-lw4over6) that are relying on it.

To try and summarise what's already out there:
The Unified CPE & lw4o6 drafts propose the use of DHCPv6 Option 64 (the DS-Lite AFTR FQDN option)
Map-dhcp describes the use of the default mapping rule (DMR) to provide the /128 of the BR

I think that it's reasonable to say that both work – I.e. They contain enough information to provision the client with the /128 of the concentrator so that it can send traffic.

Here are the arguments for/against each that I've seen. I've tried to list all the ones that I've seen, so if I've missed any, then please add them:

DHCPv6 Option 64
Pros
FQDN means that DNS round-robin load balancing could be used
Reuse of an existing option

Cons
Can not be extended with additional sub-options

map-dhcp DMR
Pros
Option has an 'encapsulated options' field, so could be extended with additional functionality (although no additional functionality has currently been proposed at this stage)

Cons
Only one DMR /128 can be provisioned to a client, so round robin load balancing can't be used
May conflict with the MAP-T (</128 prefix) DMR – Could be considered to be out of scope for this discussion, but if we are following the mechanisms described in Unified CPE so that a CPE can work out which SW mode to configure, then a dedicated MAP-T sub-option (not shared by any other mode) is needed. This is related to conversations that I've had around extending the Unified CPE model for other softwire approaches.

My view: If there is additional functionality required in this option, over an above the provisioning of a /128 prefix for the concentrator, then the MAP DMR (limited to MAP-E) is the clear choice. However, if no such functionality is needed, then we should re-use Option 64.

Cheers,
Ian

---

From: Ole Troan <[email-masked]>
Date: Fri, 26 Apr 2013 10:39:20 +0200

Ian,

> FQDN means that DNS round-robin load balancing could be used

RFC6334 specifies that only the first AAAA should be used.

> Can not be extended with additional sub-options

the CE needs to deal with DNS TTL and the added complexity of having the resulting "lifetime" of the
default router be different than the lifetime of the address/mechanism.

only one BR can be configured

> Only one DMR /128 can be provisioned to a client, so round robin load balancing can't be used

you can use anycast.

> My view: If there is additional functionality required in this option, over an above the provisioning of a /128 prefix for the concentrator, then the MAP DMR (limited to MAP-E) is the clear choice.…

does anyone know why a FQDN (with restrictions) was chosen for DS-lite?

considerations:
 - MAP: should BR be inside or outside of the domain. if inside use an IPv4 address, if outside use an IPv6 address.
   (I believe we have agreed on outside, and for LW46 it must always be outside).
 - should the CE have multiple BRs? and if so, what should it do between them? load-balance?
   the choice in 6rd was to allow for multiple BRs, but not specify how multiple BRs could be used

my preference is for a simple list of IPv6 BR addresses. i.e. none of the two above options.

cheers,
Ole

---

From: "Rajiv Asati (rajiva)" <[email-masked]>
Date: Fri, 26 Apr 2013 15:12:44 +0000

I really don't see the need for having to specify more than one BR
prefixes (of whatever length) inside a single MAP domain. Let alone FQDN
or list of IP addresses.

The reason is that having multiple BR prefixes in the same domain would at
best allow the upstream traffic to go to different BR. But it would
nothing to differentiate the downstream traffic, as it can come from any
BR. So, load-splitting would be very poor and yield no benefit. As far as
availability is concerned, then any casting is already good enough.

After all, most 6rd deployments stick with a single BR prefix.

Lastly, it would be a severe mistake of ours to limit the BR to a prefix
of /128 length. As few other operators (e.g. Reliance) have already noted
their use of MAP-T, it would be prudent for the same provisioning option
to work with it. Thankfully, this is correctly specified in the map-dhcp
draft.

Cheers,
Rajiv

-----Original Message-----
From: Ole Troan <[email-masked]>
Date: Friday, April 26, 2013 4:39 AM
To: Ian Farrer <[email-masked]>
Cc: Softwires-wg list <[email-masked]>
Subject: Re: [Softwires] Provisioning Format for CPE BR/lwAFTR Address

>Ian,
>
>> Sorry to dig this one up again, but although there has been a fair bit
>>of discussion around the topic, I don't think that we have so far
>>reached an agreement on how to provision sw CPEs with the address of the
>>concentrator for MAP-E and lw4o6. We need to get a final answer on this
>>as there's a few drafts (softwire-unified-cpe, softwire-map-dhcp,
>>softwire-lw4over6) that are relying on it.
>> 
>> I think that it's reasonable to say that both work  I.e. They contain
>>enough information to provision the client with the /128 of the
>>concentrator so that it can send traffic.
>> 
>> Here are the arguments for/against each that I've seen. I've tried to
>>list all the ones that I've seen, so if I've missed any, then please add
>>them:
>> 
>> DHCPv6 Option 64
>> Pros
>> Option has an 'encapsulated options' field, so could be extended with
>>additional functionality (although no additional functionality has
>>currently been proposed at this stage)
>> 
>> Cons
>> May conflict with the MAP-T (</128 prefix) DMR  Could be considered to
>>be out of scope for this discussion, but if we are following the
>>mechanisms described in Unified CPE so that a CPE can work out which SW
>>mode to configure, then a dedicated MAP-T sub-option (not shared by any
>>other mode) is needed. This is related to conversations that I've had
>>around extending the Unified CPE model for other softwire approaches.
>> 
>> My view: If there is additional functionality required in this option,
>>over an above the provisioning of a /128 prefix for the concentrator,
>>then the MAP DMR (limited to MAP-E) is the clear choice. However, if no
>>such functionality is needed, then we should re-use Option 64.
>
> - MAP: should BR be inside or outside of the domain. if inside use an
>IPv4 address, if outside use an IPv6 address.
>_______________________________________________
>Softwires mailing list
>[email-masked]
>https://www.ietf.org/mailman/listinfo/softwires

---

From: <[email-masked]>
Date: Fri, 26 Apr 2013 17:52:28 +0200

Hi Rajiv,

Thanks for your response. Comments in line.

Cheers,
Ian

>After all, most 6rd deployments stick with a single BR prefix.

[ian] I'm also not sure about the need for this (I certainly don't plan to
use it), but it's been raised. Do any other operators see a need for this
in their architecture?

>to work with it. Thankfully, this is correctly specified in the map-dhcp

[ian] MAP-E & lw4o6 both need a /128 for the concentrator (whether this is
supplied as a prefix or an FQDN) and will not work without this. MAP-T can
not have a /128 prefix for the DMR (/96 is the longest). MAP-E & lw4o6
wouldn't work if they were provisioned with a MAP-T DMR compatible prefix.
MAP-T wouldn't work if it was provisioned with a MAP-E / lw4o6 DMR
compatible prefix. It makes sense to have a single option/sub-option for
provisioning MAP-E and lw4o6 BRs and use a separate option/sub-option for
MAP-T.

---

From: "Rajiv Asati (rajiva)" <[email-masked]>
Date: Fri, 26 Apr 2013 16:13:37 +0000

Hi Ian,

Please see inline,

> use it), but it's been raised. Do any other operators see a need for this

Thanks for posing this Q to the other operators (and sharing your view).

> provisioning MAP-E and lw4o6 BRs and use a separate option/sub-option for

If the same option provides prefix-length and prefix, then MAP-E, -T and
lw4o6 can leverage it accordingly. This is how MAP-DHCP already does it
(for MAP modes) and could be exploited to include lw4o6.

This kinda approach is widely used in other protocols:

IPv6 RA PIO - http://tools.ietf.org/html/rfc4861#section-4.6.2
MPLS OAM - http://tools.ietf.org/html/rfc4379#section-3.2.2

Cheers,
Rajiv

-----Original Message-----
From: Ian Farrer <[email-masked]>
Date: Friday, April 26, 2013 11:52 AM
To: Rajiv Asati <[email-masked]>, Ole Troan <[email-masked]>
Cc: Softwires-wg list <[email-masked]>
Subject: Re: [Softwires] Provisioning Format for CPE BR/lwAFTR Address

>>>> The Unified CPE & lw4o6 drafts propose the use of DHCPv6 Option 64
>>>>(the
>>>>DS-Lite AFTR FQDN option)
>>>> Map-dhcp describes the use of the default mapping rule (DMR) to
>>>>provide
>>>>the /128 of the BR
>>>> 
>>>my preference is for a simple list of IPv6 BR addresses. i.e. none of
>>>the
>>>two above options.
>>>
>>>cheers,
>>>Ole