Subject: RE: [dhcwg] Renumbering Requirements for Stateless DHCPv6

From: Changming Liu <[email-masked]>
Date: Wed, 3 Mar 2004 00:32:52 -0800

Hi Ted, 

>Your scenario seems like a configuration error.   Setting things up so 
>that the client has to update DNS server information immediately on a 
>frequent basis is simply bad network design.   I don't think the goal 
>of this renumbering effort is to accommodate that kind of 
>configuration.   The right way to fix this is to put a DNS cache 
>downstream of the flaky link.

If I  was not clear in describing the scenario, pleae forgive me. Our
customer is one of the biggest Telecoes in the world. Without their
permission, I can not disclose too much details. Needless to say, it should
not be that bad design after so many engineers working on it. 

Let me try it again in different way. Let's say a multi-homed CPE with two
upstream links, one connected to one of its ISPs, one is primary and one is
backup. DHCP are enabled on both links for configuration info such as DNS.
These two ISPs offer different DNS servers. The requirement is that as long
as primary ISP is up, use it right away including DNS. This is due to cost
struture. Is this reasonable requirement? 

This CPE runs DHCP server on the downstream link to pass the DNS info to the
local LAN. Once the primary ISP is up, its DNS info neends to push to
downstream. Of course, you an hope the primary links never goes down
unplanned(if it is true, why dualhome at the first palce?). The lifetime
solution does not solve this problem.

If you need more info, we can get together to discuss this.

Changming
Netscreen Technoloies Inc

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From: "Bernie Volz" <[email-masked]>
Date: Wed, 3 Mar 2004 08:48:36 -0500

For this situation, why don't you advertise BOTH DNS servers (primary and
secondary) and simply have the CPE do the proper routing? If the primary
link is up, the CPE sends the packets over the primary link. If the primary
is down, the CPE sends the packets over the secondary link. Using the
routing infrastructure and CPE knowledge of which link is up or down seems
to me to be the best solution.

Note that you need to do this anyway with any active sessions that are
running - as I'm sure your big customer doesn't want all sessions to be
broken.

It seems to me, unless I don't understand something, there really is no
issue here.

- Bernie

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Changming Liu
Sent: Wednesday, March 03, 2004 3:33 AM
To: 'Ted Lemon '; Changming Liu
Cc: '''JINMEI Tatuya / ???? ' ' '; [email-masked] ' ' '; '''Tim Chown ' '
'
Subject: RE: [dhcwg] Renumbering Requirements for Stateless DHCPv6

Hi Ted, 

Changming

---

From: Mark Stapp <[email-masked]>
Date: Wed, 03 Mar 2004 09:05:53 -0500

or the CPE could supply its own address (if it has an address on the 
downstream link) as the dns server address, and act as a forwarder for its 
clients. the CPE knows which upstream links and upstream dns resolvers to 
use, so it should make the decision, not the clients. the downstream 
clients should be insulated from upstream network issues as much as 
possible, imo. I agree with Bernie: this doesn't sound like a problem that 
should be solved by reconfiguring the clients repeatedly.

-- Mark

---

From: JINMEI Tatuya / 神明達哉 <[email-masked]>
Date: Thu, 04 Mar 2004 00:13:48 +0900

>>>>> On Wed, 3 Mar 2004 08:48:36 -0500, 
>>>>> "Bernie Volz" <[email-masked]> said:

> to me to be the best solution.

I read the scenario

>> The requirement is that as long
>> struture.

to mean that we do not want to use the secondary DNS (which would be
located in the secondary ISP) if the primary ISP is up, due to the
cost reason (and perhaps reachability/latency issue also?).

I've not reached a conclusion (of myself) on whether or not this is
really a serious issue that can be a show-stopper for the lifetime
proposal.  However, at least I think Changming has some valid points.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]

---

From: "Bernie Volz" <[email-masked]>
Date: Wed, 3 Mar 2004 10:38:44 -0500

>cost reason (and perhaps reachability/latency issue also?).

I don't know of anyone that charges for use of the DNS to resolve addresses,
do you? Latency could be an issue; but that all depends on the routing
infrastructure (the secondary link might be slower than the primary, but if
the primary link is up, you'll use the primary link). Place the primary DNS
first in the list and it should be preferred; yes there may be some latency
before the DNS resolvers switch back to using the primary, but you'll always
have some small issue like that. It could also be that the secondary DNS
provider won't accept queries from the primary providers addresses, and in
that case you'll have the normal failover between the two DNS servers
(resolver will try primary and give up after a timeout and try secondary).
Note that the hosts (clients) would likely be using the provider's address
as the source address (I'd presume the CPE would advertise both prefixes and
the client would configure addresses on both).

Also, if the DNS fails because of addressing issues, what does that say
about any open sessions (or connections)? In order for this to be
successful, the two providers will have to have some agreement between them
to cross route packets and the DNS (and any other essential services) would
just have to be part of that. Remember, the providers are after the best
experience for the customer - or if they're not, they'll loose customers.

>proposal.  However, at least I think Changming has some valid points.

Look, you can always find an argument against any solution or at least to
reduce the effectiveness of that solution. But remember that keeping it
simple is the best. Needlessly reconfiguring clients is no way to go. It
also has latency issues since transactions could be in progress or clients
might miss the first (or first few) reconfiguration signals.

Putting all this in the routing logic of the CPE means that all the smarts
about what to do is located in ONE place and all traffic is treated equal.
This, to me, is such a basic routing issue that moving it up to any other
layer is, frankly, stupid.

- Bernie

-----Original Message-----
From: JINMEI Tatuya / _–¾’BÆ [mailto:[email-masked]] 
Sent: Wednesday, March 03, 2004 10:14 AM
To: Bernie Volz
Cc: 'Changming Liu'; [email-masked]
Subject: Re: [dhcwg] Renumbering Requirements for Stateless DHCPv6

I read the scenario

					JINMEI, Tatuya

---

From: Ted Lemon <[email-masked]>
Date: Wed, 3 Mar 2004 16:52:30 -0600

> struture. Is this reasonable requirement?

Sure.   The right way to do this is to set up a DNS caching server that 
normally contacts the primary ISP's DNS server to resolve queries, but 
will contact the secondary if the primary doesn't answer.   This allows 
for automatic failover, with no significant time delay.   If it's set 
up right, the user shouldn't even notice when the switch happens.

The point is that the wrong way to do it is to do it with DHCP.   The 
DNS protocol is already designed to correctly handle the situation 
you're describing, so there's no reason to place the burden on the DHCP 
protocol to solve this problem.