Ethernet Switches & Routers

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Occasional Contributor
Posts: 13
Registered: ‎01-17-2011

IPv6 DHCP relay

Hi there,

Does someone here have some experience using DHCPv6 on a Windows 7 host when the DHCP server is on another subnet?

On my lab, "DHCPv6 Adertisement" are ignored on my Windows7 host, when the DHCP server is on another subnet. But:

- If I put my Windows7 host in the same subnet than my DHCPv6 server, everythings runs fine.

- If I use a DHCPv6 dibbler host (ie. linux host) in the other subnet, the DHCPv6 is working as expected.

I use a MLX with image 5100c for routing, and options like "ipv6 dhcp-relay-dest", "ipv6 nd managed-config-flag", "ipv6 nd prefix-advertisement" are configured as expected.

Regards,

Vincent

Super Contributor
Posts: 1,087
Registered: ‎12-13-2009

Re: IPv6 DHCP relay

Hi,

     Not sure what DHCPv6 server you are using, but if Win 2008 then please look at this Kb

A DHCPv6 server that is running Windows Server 2008 may drop the DHCP relay-forwarded packets if these packets contain some unknown options

http://support.microsoft.com/kb/972962

May or may not help.

Thanks

Michael.

Occasional Contributor
Posts: 13
Registered: ‎01-17-2011

Re: IPv6 DHCP relay

Hi mschipp,

I use ISC DHCPv6 v4.2.1.

In fact, I've open a case. I'll update this thread when I have more information.

Regards,

Vincent

Super Contributor
Posts: 1,087
Registered: ‎12-13-2009

Re: IPv6 DHCP relay

ok thanks Vincent, I would also like to know what the issue is.

Thanks

Michael.

Occasional Contributor
Posts: 7
Registered: ‎01-22-2011

Re: IPv6 DHCP relay

Just as a quick question for my own edification. How is the server in the same/different subnet prior to having its address assigned by the DHCP service?

Ken

Occasional Contributor
Posts: 13
Registered: ‎01-17-2011

Re: IPv6 DHCP relay

Hi Ken,

The server works just as expected. Brocade support has identified the issue (relay based).

Now, I've to wait for the fix to be released.

Occasional Contributor
Posts: 18
Registered: ‎02-04-2013

Re: IPv6 DHCP relay

Hi Vincent --

Here's a DHCPv6 summary I put together after boiling in pretty much the same oil you appear to have started out in (I'm still looking for a good relay solution -- I have 120 subnets to manage).

...and let me know if this needs any tweaking -- I was pretty thorough with my fact checking but another set of eyes is always welcome!

Cheers!

Robery

Immutable Rules:

DHCPv6 doesn't work like DHCPv4.

The host gets its link-local address before doing anything else.

The host only uses DHCP to get a routable-scope address if told to by a router advertisement.

DHCPv6 servers listen on UDP port 547

DHCPv6 clients listen on UDP port 546

The whole conversation takes place in the local scope.

Details:

Per section 13 of RFC 3315 all client messages are sent to the following reserved multicast address:

Link local scope

FF02:0:0:0:0:0:1:2             All-dhcp-agents

A DHCPv6 Conversation:

DhcpV6 server link-local address:             fe80::0011:22ff:fe33:5566

DHCPv6 client link-local address:              fe80::aabb:ccff:fedd:eeff

DHCPv6 client sends Solicit:              :546  --->   :547

DHCPv6 server sends Advertise:      :546  <---   :547 

DHCPv6 client sends Request:          :546  --->   :547

DHCPv6 server sends Reply:              :546  <---   :547

DHCPv6 across subnets:

No. link-local addresses are not routable.

Either the DHCPv6 server or a DHCPv6 Relay Agent has to be on the local link.

Occasional Contributor
Posts: 13
Registered: ‎01-17-2011

Re: IPv6 DHCP relay

DEFECT000363769


Occasional Contributor
Posts: 18
Registered: ‎02-04-2013

Re: IPv6 DHCP relay

Thanks, Vincent -- I'm trying to figure out how to roll out IPv6 on nearly 150 subnets that are test environments and the absence of an IPv6 "IP Helper" function is really complicating the whole centralized address management issue. The info I posted helped clarify things here, I tghought maybe it might be useful to others as well. Thanks for the defect number -- I was about to go searching for it -- and if you know of anyone who may have made progress toward a working solution at any level (Brocade or whatever), I'd really appreciate a referral --

Thanks again!

Robert  

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