IPv6 dual-stack wireless clients and interface groups (VLAN select)

Johannes Luther · ‎09-07-2015

Hi WLAN community,

I have a tiny question regarding IPv6 dual-stack clients in combination with VLAN select (interface groups).

Regarding to the following documents this combination is not recommended:

"Note: It is not recommended to mix IPv4 and IPv6 dual stack clients in the same Interface Group."

Source: Wireless LAN IPv6 Client Deployment Guide (http://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-0/IPV6_DG.html#pgfId-76764)

"VLAN Select should not be used in a dual-stack environment" [...] "Client can get an IPv4 address from one VLAN and IPv6 address from another"

Source: Cisco Live Breakout Session (BRKEWN-2006)

So far so good. Now the question is, how to solve the IPv4 subnet scaling problem if there are dual-stack clients in an easy way.

Option 1.) IPv4 subnet scaling by using AP groups and map the SSID to different VLANs geographically. But this could be hard for existing deployments. Also the problem of "all wireless clients move to the auditorium for the company meeting" still exists when using AP groups for subnet scaling (because there is only one /24 for all APs in the auditorium). In my opinion interface groups are the more elegant approach.

Option 2.) IPv4 subnet scaling by decreasing prefix length (e.g. /24 to /23). But in networking kindergarden I learned that big subnets are not a good thing to do. Ok - with a centralized WLC by blocking of broadcast traffic at the WLC or p2p blocking the problem is not as severe as in the wired network... but still - It's not a good design. More over scaling only works by doubling the existing subnet - could be a waste if you need 5000 clients and assign a prefix of /19 for ~8000 clients.

To be honest I'm not glad with the outlined options. Interface groups are a great feature and in my opinion the customers need this feature.

Are there other ways to deal with dual-stack clients? Lets imagine you have 2500 dual-stack wireless clients in a site with one centralized controller. How would you solve this task?

Or is the recommendation not to use interface groups with dual-stack clients not valid anymore and somehow "fixed" in current 8.x releases?

Thanks in advance for the discussion on this topic!

Cheers

Johannes

Johannes Luther · ‎04-20-2016

I hate guys who are pushing threads like this ... but anyway 🙂

I think the above is a very interesting thing to discuss. How did you solve IPv6 dual-stack clients scaling? Large IP subnets, Interface groups (yeah) or AP groups?

Anybody know the reason why interface groups are not recommended in combination with IPv6?

Johannes Luther · ‎04-27-2016

A very skilled WLAN guy from Cisco found an answer to my question. Just in case anybody stumbles upon the same question:

https://bst.cloudapps.cisco.com/bugsearch/bug/CSCut36511

Symptom:
Interface group feature on dual stack networks

Conditions:
vlan select feature on dual stack networks.

Any wireless controller running version 7.6 and above

Workaround:
Removing this statement as dual stack deployment works with vlan select feature since Air OS code 7.6

So the recommendation is obviously no longer valid for 7.6 releases and above!