IPV6 DHCP stateful doesn't insert local subnet in route table

[tato386]

I am setting up IPV6 on a LAN using satic IPs for Win2008 servers and DHCP stateful mode for Win7 clients.  All static assigned servers can ping each other and if I setup a static on the Win7 clients they can also ping the servers.  However when I assign DHCP stateful mode IP to the clients they lose the ability to ping the servers.  I think that was is going on is that when the Win7 machines get IP via DHCP they do not get a route in the routing table for the local subnet.  I have included IP info for static and DHCP clients in attachments.

I figure if I could add the fd:0:0:1::/64 subnet to the DHCP client it would work but I haven't been able to find the correct syntax to add an "on-link" router.  Furthermore, this would kind of defeat the purpose of DHCP if I had to manually add routes to clients.

I have a UC520 that is the default gateway on the LAN and seems to support IPV6.  Maybe this guy can help me out?

Thanks in advance.

[cadet alain]

Hi,

It seems you were assigned a /128 by the DHCPv6 server but it won't work if it is not a /64.

Can you provide  sh run output from the UC520? Are you sure you're doing stateful DHCP? Sniff interface and send pcap file also in addition to running config from router or is the dhcp server a windows/linux box?

To add an IPv6 route in windows you must use the netsh utility:

http://technet.microsoft.com/en-us/library/cc758702%28WS.10%29.aspx

Regards.

Alain

[tato386]

Alain,

I disagree about the /128.  If you look at the static host it also has a /128 route pointing to itself.  Also the IPV4 also shows /32 routes pointing to the local IP.  The static host has one additional route not found on the DHCP client which is the /64 route to the local subnet pointing to "on-link". It is not clear how to add an "on-link" route using netsh but my point is that DHCP should provide all info and relying on manually adding routes is not the optimal solution.

The UC520 does not have any IPV6 on it.  I only mentioned it because usually I use Windows for DHCP but in this case Windows is giving me this weird behaviour.  I would rather get Windows DHCP to solve the problem but if it can't I would use the UC520 as a backup option.

Thanks for your input.

Rgds,

Diego

[Ole Troan · Accepted solution]

DHCPv6 works somewhat differently than it's IPv4 counterpart.

DHCPv6 does not pass any prefix / subnet mask information. That is done using ND (Neighbor Discovery).

ND is also used to pass a default router. Therefore to get information of onlink prefixes to the host

you need to include that in RA (ND Router Advertisements) sent by the default router. Just configuring an

IPv6 address on the interface with a /64 prefix length will do the trick.

cheers,

Ole

[tato386]

Seems like you are right.  I find it odd that DHCPV6 now requires me to have two devices involved in the mix.  I usually do all my DHCP IPV4 stuff on a Windows server which gives me a nice GUI and plenty of tools to work with.  Now it seems like I can do some of it on Windows but need to get the router involved also.  I am guessing that I will eventually find how this makes things easier!

Thanks,

Diego

[Ole Troan]

DHCPv6 doesn't require you to have two devices. You have two devices in IPv4 too.

You do have a default router, right? So, we have only moved a couple of functions around. Where router discovery and prefix discovery makes more sense to come from one source. In IPv4 you needed to configure that information in both the DHCP server and the router.

cheers,

Ole