Subject: [dhcwg] Default Route configured by DHCPv6?

From: Alexandru Petrescu <[email-masked]>
Date: Fri, 10 Sep 2010 23:41:35 +0200

Hello DHC,

I am not updated with latest advancements, sorry.   The discussion comes
from the draft-ietf-mext-nemo-pd-06 LC of IESG recently.

I need a default route configured automatically in the Mobile Router
connected at home.

Is it possible that the DHCPv6-PD specification to allow for the
creation of a default route on the Requesting Router? (in addition to
configuring a Prefix on it).

A Mobile Router (Mobile IPv6, NEMOv6) connected on home link acquires a
Prefix (Mobile Network Prefix) from a DHCPv6 Server using the DHCPv6-PD,
a little bit like draft-ietf-mext-nemo-pd-06.  This is very encouraging
because it automates almost everything in the bootstrapping of a Mobile
Router:  it acquires an address too (the Home Address), the resolver,
etc.  However it does not acquire a default route w/o which nothing
leaves from the moving network.

This being a Router it does not self-configure a default route from
SLAAC either.

Is this a software problem only?  (i.e. DHCPv6-PD does allow this
creation of default route, yet software doesnt yet implement, or so).

Does DHCPv6 and DHCPv6-PD text forbid the creation of this default route
on a Requesting Router? (as opposed to DHCPv4 which does create a
default route on a Client).

Is there in DHCPv6-PD an assumption that the default route on the
Requesting Router is always the Delegating Router? (and not the Relay,
for example).

Is there already a draft in DHC which proposes to create this default
route with DHCPv6?

Would there be any opposition if I wrote a draft about DHCPv6 setting
the default route on the Client (as DHCPv4 does) in DHC group?

Comments appreciated.

Alex

---

From: Ted Lemon <[email-masked]>
Date: Fri, 10 Sep 2010 22:53:05 -0400

> the default route on the Client (as DHCPv4 does) in DHC group?

I'm pretty sure this is going on the MIF charter, actually, so you might want to talk to them first.

---

From: Ole Troan <[email-masked]>
Date: Sat, 11 Sep 2010 08:58:53 +0200

Alex,

http://datatracker.ietf.org/doc/draft-ietf-v6ops-ipv6-cpe-router/

requirement W-3 talks about how to create a default route for this type of router.

cheers,
Ole

On Sep 10, 2010, at 23:41 , Alexandru Petrescu wrote:

> _______________________________________________
> dhcwg mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/dhcwg

---

From: Alexandru Petrescu <[email-masked]>
Date: Sat, 11 Sep 2010 13:44:34 +0200

Le 11/09/2010 04:53, Ted Lemon a écrit :
>> Would there be any opposition if I wrote a draft about DHCPv6
>> setting the default route on the Client (as DHCPv4 does) in DHC
>> group?
>

Ah right, MIF charter proposal talks DHCP options for route table
configs which seems promissing.  I will go there ask. I worry they'll
say my MR is not using multiple interfaces (it's a simple Router with a
single egress interface, running DHCPv6-PD), but let me try.

Alex

---

From: Alexandru Petrescu <[email-masked]>
Date: Sat, 11 Sep 2010 14:03:41 +0200

> requirement W-3 talks about how to create a default route for this

Thanks!  That kind of req is what I am looking for.

However, I believe it a little bit subject to questioning.  As it stands
now it says in draft-ietf-v6ops-ipv6-cpe-router:
> W-3:  Absent of other routing information the IPv6 CE router MUST
> use Router Discovery as specified in [RFC4861] to discover a default
> router(s) and install default route(s) in its routing table with the
> discovered router's address as the next-hop.

The CE Customer Edge seems to be a Router and rfc4861 says "host
receives Router Advertisements from all routers, building a list of
default routers." Remark it does not say a "Router" but a "host".  In
practice, if I set forward=1 (make it a Router instead of Host) the
Mobile Router will not synthesize a default router entry in its Default
Router list.

This bothers me a lot, because I need to dynamically change this
machine's interface from Host (get default route) to Router (get prefix
with DHCPv6-PD) and back to Host when it moves away from home and sends 
BUs; and cycle through these behaviours depending on which protocol is 
used (Mobile IPv6, DHCPv6-PD, ND, SLAAC).

Were DHCPv6-PD spec to say: a Router, contrary to rfc4861, is allowed to
synthesize a default router entry in its default router list upon
reception of a Router Advertisement; or otherwise get a default route
from DHCPv6-PD.

I may have other requirements to add to DHCPv6-PD - like allow the use
of Relay (currently only DR and RR are described), or allow updating
routing table on Relay... but currently default route is what bothers.

This is for Mobile Router context - things move - as opposed to CPE
context of fixed routers, in which I agree Relay may not be needed(?).

Thanks for the pointer.

Alex

> cheers, Ole
>> I am not updated with latest advancements, sorry.   The discussion
>> comes from the draft-ietf-mext-nemo-pd-06 LC of IESG recently.
>>
>> I need a default route configured automatically in the Mobile
>> Router connected at home.
>>
>> creation of a default route on the Requesting Router? (in addition
>> to configuring a Prefix on it).
>>
>> A Mobile Router (Mobile IPv6, NEMOv6) connected on home link
>> acquires a Prefix (Mobile Network Prefix) from a DHCPv6 Server
>> using the DHCPv6-PD, a little bit like draft-ietf-mext-nemo-pd-06.
>> This is very encouraging because it automates almost everything in
>> the bootstrapping of a Mobile Router:  it acquires an address too
>> (the Home Address), the resolver, etc.  However it does not acquire
>> a default route w/o which nothing leaves from the moving network.
>>
>> This being a Router it does not self-configure a default route
>> from SLAAC either.
>>
>> Does DHCPv6 and DHCPv6-PD text forbid the creation of this default
>> route on a Requesting Router? (as opposed to DHCPv4 which does
>> create a default route on a Client).
>>
>> Requesting Router is always the Delegating Router? (and not the
>> Relay, for example).
>>
>> Is there already a draft in DHC which proposes to create this
>> default route with DHCPv6?
>>
>> Alex _______________________________________________ dhcwg mailing
>> list [email-masked] https://www.ietf.org/mailman/listinfo/dhcwg
>
>

---

From: Ole Troan <[email-masked]>
Date: Sat, 11 Sep 2010 22:41:06 +0200

Alex,

> Mobile Router will not synthesize a default router entry in its Default

in this context the upstream or WAN side interface is acting as both. it does some host functions of ND, like acquiring an address and doing router discovery, while forwarding packets as a router. it is not expected that it switched from one "role" to another.

cheers,
Ole

> with DHCPv6-PD) and back to Host when it moves away from home and sends BUs; and cycle through these behaviours depending on which protocol is used (Mobile IPv6, DHCPv6-PD, ND, SLAAC).
>

---

From: Alexandru Petrescu <[email-masked]>
Date: Sun, 12 Sep 2010 16:35:11 +0200

Le 11/09/2010 22:41, Ole Troan a écrit :
>> However, I believe it a little bit subject to questioning.  As it
>> stands now it says in draft-ietf-v6ops-ipv6-cpe-router:
>>> W-3:  Absent of other routing information the IPv6 CE router
>>> MUST use Router Discovery as specified in [RFC4861] to discover a
>>>  default router(s) and install default route(s) in its routing
>>> table with the discovered router's address as the next-hop.
>>
>> receives Router Advertisements from all routers, building a list
>> of default routers." Remark it does not say a "Router" but a
>> "host". In practice, if I set forward=1 (make it a Router instead
>> of Host) the Mobile Router will not synthesize a default router
>> entry in its Default Router list.
>
> in this context the upstream or WAN side interface is acting as both.
> it does some host functions of ND, like acquiring an address and
> doing router discovery, while forwarding packets as a router. it is
> not expected that it switched from one "role" to another.

Hmm... sounds reasonable to describe it as such.  I optimistically
assume all router-vs-host specific aspects in rfc4861 are clear not just
some (joining host-vs-router mc groups, sending or not RAs, etc.), on 
the WAN side interface of CE, the one acting as both host and router.

In linux this doesn't work, because if forward==1 then it doesn't
acquire a default route with SLAAC (neither a global address); if
forward==0 then it does not forward packets.  Or am I overlooking some
recent radvd and/or procsys options maybe.

Alex

---

From: Ole Troan <[email-masked]>
Date: Sun, 12 Sep 2010 20:58:57 +0200

> some (joining host-vs-router mc groups, sending or not RAs, etc.), on the WAN side interface of CE, the one acting as both host and router.
> 

you have the source code. fix it. ;-)

cheers,
Ole

---

From: Alexandru Petrescu <[email-masked]>
Date: Sun, 12 Sep 2010 22:40:20 +0200

Le 12/09/2010 20:58, Ole Troan a écrit :
>>>
>>> in this context the upstream or WAN side interface is acting as
>>> both. it does some host functions of ND, like acquiring an
>>> address and doing router discovery, while forwarding packets as a
>>> router. it is not expected that it switched from one "role" to
>>> another.
>>
>> assume all router-vs-host specific aspects in rfc4861 are clear not
>> just some (joining host-vs-router mc groups, sending or not RAs,
>> etc.), on the WAN side interface of CE, the one acting as both host
>> and router.
>>
>> forward==0 then it does not forward packets.  Or am I overlooking
>> some recent radvd and/or procsys options maybe.
>

I'll cycle that forward flag looks easier :-)

Just out of curiosity - was it intentional to not configure default
routes with DHCPv6?  There's this huge set of configuration parameters
in DHCP but no default route...

Alex

---

From: [email-masked]
Date: Sun, 12 Sep 2010 23:01:11 +0200 (CEST)

> in DHCP but no default route...

Very much on purpose. The default route is supposed to be configured
by RA only. This is an old, religious discussion, see the archives for
much more. You are far from the first one asking for this capability
in DHCPv6.

Steinar Haug, Nethelp consulting, [email-masked]

---

From: Ole Troan <[email-masked]>
Date: Mon, 13 Sep 2010 07:45:32 +0200

Alex,

> in DHCP but no default route...

if you ask in the context of DHCP PD (3633); that is a protocol between _routers_ for delegating prefixes, it intentionally says nothing about how routing is done between those two routers. the expectation may have been that a routing protocol was used.

cheers,
Ole

---

From: Wojciech Dec <[email-masked]>
Date: Mon, 13 Sep 2010 11:04:21 +0200

You may also want to take a look at
http://tools.ietf.org/html/draft-dec-dhcpv6-route-option-04 , which is
likely to provide what you need.

Thanks,
Woj.

On 12 September 2010 22:40, Alexandru Petrescu <[email-masked]
> wrote:

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 16 Sep 2010 18:08:31 +0200

Le 13/09/2010 11:04, Wojciech Dec a écrit :
> http://tools.ietf.org/html/draft-dec-dhcpv6-route-option-04 , which
> is likely to provide what you need.

Thanks this is the kind of option that is interesting (in one way, there
are others) to me.  In a sense I need the default route delivered to a
Router via DHCPv6.

I am novice to DHCPv6, thanks for bearing with me.

> When processing a received Route Option a client MUST substitute a
> 0::0 value of the Next Hop Option with the source IPv6 address of
> the received DHCPv6 message.

Sounds clear to me, but I am not so clear whether that src address is
the Server's Address?  Or the Relay's ingress interface address
(interface on-link with Client's interface)?  Or the Relay's egress
interface.

> It MUST also associate a Link Local next hop addresses with the
> interface on which the client received the DHCPv6 message containing
>  the route option.

I do not understand this MUST?  What does it mean that the Client
"associates" a link-local address of a next-hop with one of its
interfaces?  Does it mean insertion of a routing table entry towards a
next-hop whose address is link-local, entry whose "dev" parameter is an
interface on which this DHCPv6 message was received?

Or something else?

> Such a substitution and/or association is useful in cases where the
> DHCPv6 server operator does not directly know the IPv6 next-hop
> address, other than knowing it is that of a DHCPv6 relay agent on
> the client LAN segment.

I am not clear whether the DHCPv6 message arrives from Server to the
Client (through a Relay) with the src address changed.  That src address
should be that of the Server.  Architecturally speaking I doubt the
Relay touches the src address (doubt, no religion), this is clarifying
question.

I am not clear whether the Server knows at all the link-local address of
Relay's interface on-link with Client.

It may be possible that the Server does know the global address of the
Relay's interface on the other side than Client.  But that address is
useless to the Client (as a next-hop for its default route).

Ideally the default route should have next-hop address a link-local
address - reduce global address waste.

> DHCPv6 Packets relayed to the client are sourced by the relay using
> this relay's IPv6 address, which could be a link local address.

I am not clear the DHCPv6 packets originated by the Server and dst
Client are touched by Relay modfiying the src address and I don't see
why should Relay do so.

Alex

>
> Thanks, Woj.
>
> On 12 September 2010 22:40, Alexandru Petrescu
> <[email-masked] <mailto:[email-masked]>>
>  wrote:
>
> routes with DHCPv6?  There's this huge set of configuration
> parameters in DHCP but no default route...
>
> Alex
>
> _______________________________________________ dhcwg mailing list
> [email-masked] <mailto:[email-masked]>