Subject: Re: Re: [dhcwg] Operational problem caused by inconsistent RA M and Oflags

From: HYUN WOOK CHA <[email-masked]>
Date: Sat, 05 Jan 2008 04:26:27 +0000 (GMT)

Dear Thomas, 

Thank you for your answer. I want to clarify this issue more. 
As for finite bindings obtained via DHCPv6,  you are right. However, after all addresses with finite lifetimes expire, DHCPv6 clients will continue to search servers to obtain stateful addresses again. IMO, this result is to be avoid from the view of the purpose of triggering DHCPv6 client using RA flags. 
In addition, if clients obtained addresses with inifinite lifetimes, there may be inefficient or bad cases where hosts will be affected by those addresses. I have no idea what is the cases, but we should consider this condition.

Joseph HyunWook Cha

------- Original Message -------
Sender : Thomas Narten<[email-masked]> 
Date   : 2008-01-04 10:41 (GMT+09:00)
Title  : Re: [dhcwg] Operational problem caused by inconsistent RA M and Oflags

HYUN WOOK CHA <[email-masked]> writes:

> Could you tell me why the M flag's change from TRUE to FALSE should
> not stop DHCPv6 clients?

Because the wording in 2462 says not to do this. Specifically, it
says:

> If the value of the ManagedFlag changes from TRUE to FALSE, the host
> should continue running the stateful address autoconfiguration,
> i.e., the change in the value of the ManagedFlag has no effect.

If DHCP is really no longer to be used (and no longer works), the
addresses obtained via DHCP will expire after their lifetime
expires. 

Thomas

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---

From: Thomas Narten <[email-masked]>
Date: Mon, 07 Jan 2008 16:05:21 -0500

HYUN WOOK CHA <[email-masked]> writes:

> As for finite bindings obtained via DHCPv6, you are right. However,
> after all addresses with finite lifetimes expire, DHCPv6 clients will
> continue to search servers to obtain stateful addresses again. IMO,
> this result is to be avoid from the view of the purpose of triggering
> DHCPv6 client using RA flags.

If no DHCP server is available, clients will back off and retry slowly
(I assume). So, this is not a serious problem. Perhaps not ideal, but
not a serious problem.

> In addition, if clients obtained addresses with inifinite lifetimes,
> there may be inefficient or bad cases where hosts will be affected by
> those addresses. I have no idea what is the cases, but we should
> consider this condition.

IMO, infinite lease times are a Bad Idea. If we had to do it over
again, I'd probably argue the protocol should not support them. In
order for things to work "properly" in practice, you need to have
routers and DHCP servers that function correctly. It just doesn't make
sense (generally) any other way. So we shouldn't be over engineering a
case where a client has a working network, but the routers or DHCP
servers are not working (for long periods of time, like hours and
days).

If a site feels that it needs to use infinite leases, they should
think through the implications (including worst case scenarios)
carefully.

Thomas

---

From: "Hemant Singh (shemant)" <[email-masked]>
Date: Mon, 7 Jan 2008 16:42:11 -0500

Joseph,

Personally, as a router person, any network I see with more than one
router serving the same link seems brain-damaged to me - at least in
corporate wired LANs or access concentrator networks like cable modem
deployments there should be only one router serving one link.

To begin with, you should not have hosts behind modems see two different
router RA's. Unless there is a very common deployment with over several
tens of millions of hosts getting affected, any problem is not serious
enough to consider for the deployment.

Lastly, even though you did reply to John's question to clarify your
deployment, I still don't understand your deployment. In replying to
John's questions on deployment scenario, you mention a modem, but the
modem is not shown anywhere in your picture. I have snipped your
original picture below.

>                                     ------------------
>                                     | ISP2                  |
>    -----------------        | Access_Router2 |
>    | ISP1                |       ------------------
>    | Acess_Router1 |                   |
>    -----------------            CPE_Router
>      |RA(P1, M=1)                        |RA(P2, M=0)
>    ------------------------------------ link0
>           |        |       |       |
>          pc1    pc2    pc3   pc4

If you perhaps keep mixing nodes like CPE router and modem, or adding
new nodes like modems to your original picture, we will never close this
thread.

Let's take a step back and please produce a better picture and then also
justify that over 10's of millions of hosts will get affected by your
problem statement.  

Thanks.

Hemant

-----Original Message-----
From: HYUN WOOK CHA [mailto:[email-masked]] 
Sent: Friday, January 04, 2008 11:26 PM
To: Thomas Narten
Cc: ???; dhc WG; ???; ???; ???
Subject: Re: Re: [dhcwg] Operational problem caused by inconsistent RA M
andOflags

Dear Thomas, 

Thank you for your answer. I want to clarify this issue more. 
As for finite bindings obtained via DHCPv6,  you are right. However,
after all addresses with finite lifetimes expire, DHCPv6 clients will
continue to search servers to obtain stateful addresses again. IMO, this
result is to be avoid from the view of the purpose of triggering DHCPv6
client using RA flags. 
In addition, if clients obtained addresses with inifinite lifetimes,
there may be inefficient or bad cases where hosts will be affected by
those addresses. I have no idea what is the cases, but we should
consider this condition.

Joseph HyunWook Cha

------- Original Message -------
Sender : Thomas Narten<[email-masked]> 
Date   : 2008-01-04 10:41 (GMT+09:00)
Title  : Re: [dhcwg] Operational problem caused by inconsistent RA M and
Oflags

says:

> should continue running the stateful address autoconfiguration, i.e., 
> the change in the value of the ManagedFlag has no effect.

If DHCP is really no longer to be used (and no longer works), the
addresses obtained via DHCP will expire after their lifetime expires. 

Thomas