Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

Bronze

CNR DHCPv6 and not /64 prefix

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.

4 REPLIES
Cisco Employee

Re: CNR DHCPv6 and not /64 prefix

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

Bronze

Re: CNR DHCPv6 and not /64 prefix

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.

Cisco Employee

Re: CNR DHCPv6 and not /64 prefix

>>>>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. <<<<

;-)

Bronze

Re: CNR DHCPv6 and not /64 prefix

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.

293
Views
4
Helpful
4
Replies