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

From: Changming Liu <[email-masked]>
Date: Wed, 3 Mar 2004 08:35:23 -0800

Bernie,

I may miss your point. The primary and backup DNS servers' addresses are
different. When switching-over from backup to primary happens, the backup's
DNS server's address can not be used any more. How does it become a routing
issue?

Changming

-----Original Message-----
From: Bernie Volz
To: 'Changming Liu'; ''Ted Lemon ' '
Cc: ''''JINMEI Tatuya / ???? ' ' ' '; [email-masked]; ''''Tim Chown ' ' ' '
Sent: 3/3/2004 6:35 AM
Subject: RE: [dhcwg] Renumbering Requirements for Stateless DHCPv6

Huh? How does this break anything? This is exactly what routing is all
about. And it is exactly what layering is all about. The application
layer
(such as DNS) shouldn't care exactly what route packets take to reach
their
destination - that's the responsibility of IP, not DNS.

As I said earlier, any active connections (or sessions) will need to be
re-routed over the link that's up and preferred, and you would not want
to
break these connections (sessions).

Note also that:
- This will be instantaneous (or as close as you can get) since the CPE
can
switch links as soon as the primary link returns (or the primary link is
marked down).
- Will redirect *ALL* traffic, which is exactly what you want.
- Is transparent to all applications and works for all applications
(anything above the IP layer).
- Allows fancier use of the two links as well - such as for load
balancing.

This is not a DHCP issue at all, but just a standard routing issue.

- Bernie

-----Original Message-----
From: Changming Liu [mailto:[email-masked]] 
Sent: Wednesday, March 03, 2004 9:20 AM
To: 'Bernie Volz '; Changming Liu; ''Ted Lemon ' '
Cc: ''''JINMEI Tatuya / ???? ' ' ' '; [email-masked] '; ''''Tim Chown '
' '
'
Subject: RE: [dhcwg] Renumbering Requirements for Stateless DHCPv6

 That could be a solutiuon. But will that break the layered model?
Currently
our routing is purely based on IP addresses. DNS is just one of the
configurations. There could be more.

Changming

-----Original Message-----
From: Bernie Volz
To: 'Changming Liu'; 'Ted Lemon '
Cc: '''JINMEI Tatuya / ???? ' ' '; [email-masked]; '''Tim Chown ' ' '
Sent: 3/3/2004 5:48 AM
Subject: RE: [dhcwg] Renumbering Requirements for Stateless DHCPv6

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, 

>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 22:37:23 -0500

Where is the primary DNS server and why can't it be used anymore?

What I assume you have is:

                            <----primary link---->
Customer network <----> CPE                        Service Provider
                            <----secondary link-->

If the DNS server is in the customer network or the CPE, there's no issue
since the links don't matter.

If the DNS server is in the service provider(s) network (which is where I
assume they are), even if the links go to separate providers, why can't
packets sent over either link reach either DNS server for resolving?

Whether packets go over the primary or secondary link shouldn't really
affect whether they reach their destination. That's why it is a routing
issue.

If there are two separate service providers, the providers will need to
agree to transit traffic to each other. But they need to do this anyway,
otherwise you'll have to renumber the customer network each time the links
flop and you end up breaking any active connections - which the customer
isn't going to like and basically means that secondary link is pretty much
worthless.

If you have some other configuration, please describe it in greater detail
so I can understand why the primary DNS server wouldn't be reachable via the
secondary link.

- Bernie
 
-----Original Message-----
From: Changming Liu [mailto:[email-masked]] 
Sent: Wednesday, March 03, 2004 11:35 AM
To: 'Bernie Volz '; Changming Liu; '''Ted Lemon ' ' '
Cc: '''''JINMEI Tatuya / ???? ' ' ' ' '; [email-masked] '; '''''Tim Chown '
' ' ' '

 Bernie,

Changming

-----Original Message-----
From: Bernie Volz
To: 'Changming Liu'; ''Ted Lemon ' '
Cc: ''''JINMEI Tatuya / ???? ' ' ' '; [email-masked]; ''''Tim Chown ' ' ' '
Sent: 3/3/2004 6:35 AM
Subject: RE: [dhcwg] Renumbering Requirements for Stateless DHCPv6

Note also that:

- Bernie

-----Original Message-----
From: Changming Liu [mailto:[email-masked]] 
Sent: Wednesday, March 03, 2004 9:20 AM
To: 'Bernie Volz '; Changming Liu; ''Ted Lemon ' '
Cc: ''''JINMEI Tatuya / ???? ' ' ' '; [email-masked] '; ''''Tim Chown '
' '
'

Changming

-----Original Message-----
From: Bernie Volz
To: 'Changming Liu'; 'Ted Lemon '
Cc: '''JINMEI Tatuya / ???? ' ' '; [email-masked]; '''Tim Chown ' ' '
Sent: 3/3/2004 5:48 AM
Subject: RE: [dhcwg] Renumbering Requirements for Stateless DHCPv6

- Bernie

-----Original Message-----

Hi Ted, 

Changming