CNR DHCPv6 and not /64 prefix

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Aug 1st, 2007

Hi,

We are using CNR for DNS and DHCPv6 and would like to handout v6 network prefixes of /119 or /120 to Windows 2003 (SP2) clients. Question is will the MS 2003 clients accept a network prefix of other than /64? (Sorry I understand this is NOT an M$ chat site) Thanks for ANY Help.

I have this problem too.
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jreekers Wed, 08/01/2007 - 20:08

Hi Frank.

Typically, the host is going to expect a /64 prefix. However, there is nothing to keep you from configuring a /119 or /120 *range* in the CNR while you still advertise a /64 to the hosts.

So to describe further, I'm not sure why would you care to hand-out v6 network prefixes of /119 or /120. CNR's range for allocation can be much smaller (larger prefix length) than the prefix advertised to the client.

So, advertise /64 to clients. Use /119 or /120 if you want in CNR.

It's transparent to your hosts this way...they expect and get a /64 prefix, and you get the benefit of a /119 or /120 range in the CNR (totally transparent to the hosts).

Hope this helps and hasn't confused further. :-)

-J

fsebera Thu, 08/02/2007 - 04:41

Hi J,

First thanks for the reply. It appears there are NOT many folks interested in v6 - yet.

Here is what I understand

Mask.....# of Host in network

/128.....1

/127.....2

/126.....4

/125.....8

/124.....16

/123.....32

/122.....64

/121.....128

/120.....256

/119.....512

/118.....1024

/etc...../etc

So if I wanted a network to match my current class "C" of 254 host, I would use a /120.

When I present the Win2003 host with a network prefix of ANYTHING other than a /64 the host ignores the prefix and does not accept the prefix. The host just has a link local address and cannot get off the local net, no gateway, no DNS, No NTP etc. I understand the host wants a /64 so it will EUI it's MAC address to have a 128 bit unique address and that is fine. I was hoping for another way to present the host with a prefix/host address via CNR and leave the EUIed MAC address out of the equation completely. I had hoped the Win Clients would just accept the CNR presented v6 addresses as presented. Perhaps M$ wants us to buy the new Vista client as it does have a DHCPv6 client where as the Win2003/WinXP clients do not have such a client.

If I understand correctly, CNR can hand out network prefixes of ANY size but the end client must be programmed with the correct DHCP software to accept the CNR presented prefix. -RIGHT?

On a side note and not intended to be a slam on anyone!

Oh and yes I understand the idea that v6 addresses are enormous but isn't this the same thing we thought about the first PC memory and the original IPv4 address space - just give it out freely, we have plenty. Ha.

jreekers Thu, 08/02/2007 - 15:23

>>>>If I understand correctly, CNR can hand out network prefixes of ANY size but the end client must be programmed with the correct DHCP software to accept the CNR presented prefix. -RIGHT? <<<<

That is correct.

>>>>On a side note and not intended to be a slam on anyone!

Oh and yes I understand the idea that v6 addresses are enormous but isn't this the same thing we thought about the first PC memory and the original IPv4 address space - just give it out freely, we have plenty. Ha. <<<<

;-)

fsebera Fri, 08/03/2007 - 04:38

Thanks for the conformation as this is what our wire-shark sniffer traces have been revealing to us.

BTW, Anyone know of a Win2003 or WinXP DHCP add-on client that would allow the OS to accept an address prefix smaller than /64?

If no add-on client for Win2003 or WinXP then we have four choices:

1. Accept the /64 prefix and be happy.

2. Static assignments with a /119 to match our current /24 IPv4 address network setup

3. Switch to a different OS (Other than M$)

4. Upgrade hardware and OS to support Vista

While a /64 network prefix provides about:

17,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 possible nodes on the same broadcased (FF01::1), one would think the "brains" would have setteled on a little bit smaller network size - but hey this is just me.

Thanks again for the help.

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