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Community Member

VLAN Select and IPv6

Hello group,

we are having some issues with the combination of IPv6/dualstack on our WLANs (which we had for quite some time) and the use of the VLAN Select-feature of our WISMs (Code:

Due to the nature of VLAN Select, the clients can hear the multicasts from both VLANs, so they can hear the IPv6-RAs from both IPv6-routers. The clients then calculate an IPv6-Address for both routers (of which, only one is reachable - the one in the same VLAN as the client) and then some weird stuff happens, depending on the IPv6-Stack of the client-OS.

It seems that Linux-Clients have some trouble with this, leaving both routers on REACH or STALE, because the client receives RAs all the time. So even if there is no possibility for the client to reach the router in the other VLAN, it never marks it as UNREACH. So the client loses connectivitiy, if it chooses the wrong default gateway, depending on coincidence. First reports indicate, that Android phones (so a Linux-IPv6-Stack as well) suffer from the same flaw.

This does not affect IPv4, because in IPv4 the client does DHCP - so the client initiates the process for getting an address, versus the router sending RAs. So in a pure IPv4-Network, there is no chance of that becoming a problem.

So, my question: Does anybody run dualstack with VLAN Select? How to resolve this issues? The "multicast VLAN" feature with VLAN select is the exact opposite of what should happen...

Cisco Employee

Re: VLAN Select and IPv6

is it wism1 or wism2. if wism2 could you try with code.   

The interface groups feature allows an  organization to have a single WLAN with multiple VLANs configured on the  controller in order to permit load balancing of wireless clients across  these VLANs. This feature is commonly used to keep IPv4 subnet sizes  small while enabling a WLAN to scale to thousands of users across  multiple VLANs in the group. In order to support IPv6 clients with  interface groups, no additional configuration is required as the system  automatically sends the correct RA to the correct clients via L2  wireless unicast. By unicasting the RA, clients on the same WLAN, but a  different VLAN, do not receive the incorrect RA.

Community Member

VLAN Select and IPv6

those are 4 WiSM1s.

but this feature sounds exactly like the solution to this problem - which makes it the third nice feature we can't use because 7.2 is wism2 only. (after IPv6-security and sticky-key-caching) :-(

Cisco Employee

VLAN Select and IPv6

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