Router advertisement unicast conversion

For IP version 6 (IPv6) deployments, IPv6 hosts rely on router advertisements (RAs) for host addressing, other information and router discovery. RAs are transmitted by IPv6 routers on their assigned link (i.e. VLAN) and are either solicited by IPv6 hosts or periodically advertised at a configured interval. RAs are a type of control message (type 134) within the internet control message protocol version 6 (ICMPv6) framework. When configured, RAs are transmitted by IPv6 routers on each VLAN with the destination multicast address ff02::1. By default these frames are transmitted to wireless stations at the WLANs lowest configured transmit rate. RAs are an important element for IPv6 host addressing and router discovery. Their transmission as broadcast multicast frames by APs is problematic when VLAN pooling or dynamic VLAN assignment is enabled in a WLAN as RAs originating from different VLANs will be received by all IPv6 hosts associated with the BSSID. Without additional RA optimization:

1. IPv6 hosts can derive global addressing from an incorrect VLAN.
2. IPv6 hosts may discover and install IPv6 routers from an incorrect VLAN. Both situations resulting in poor user or application experience.

Recommendation

No action is required if a WLAN does not support IPv6 wireless hosts or a single VLAN architecture is deployed. RA optimization is only required if a WLAN supports IPv6 hosts if VLAN pooling or dynamic VLAN assignments is implemented. In these deployments HPE Aruba Networking recommends enabling the IPv6 RA and ND optimization feature in the WLAN profile. When the IPv6 RA and ND optimization feature is enabled in a WLAN profile, APs will convert RAs received on a given VLAN with active wireless stations to unicast. The APs replaces the receiver address in the frame header with each wireless stations host MAC address and will transmit the RA at each station’s unicast transmit rate. The AP will replicate and forward each received RA on a VLAN to each active station assigned to that VLAN. For example, if a BSSID has ten stations assigned to VLAN 20, the AP will forward a separate unicast copy of an RA received on VLAN 20 to all ten stations.

Configuration

RA unicast conversion is enabled within each WLAN profile. In classic Central, IPv6 RA and ND optimization is configured for each WLAN under Broadcast/Multicast

New Central includes intelligent defaults for each WLAN profile based on the Network Configuration selection. The selected Network Configuration option determines if IPv6 RA and ND optimization is applied to each WLAN profile:

• Most Compatible – Disabled
• Balanced – Enabled
• High Density – Enabled
• Custom – User defined

A custom broadcast filtering option is configured under Broadcast/Multicast

Before and after

The following packet capture depicts RAs that are forwarded as multicast frames at the minimum configured transmit data rate. The receiver’s destination address is a multicast address(33:33:00:00:00:01) and the RAs are received by all wireless stations associated with the BSSID irrespective of their VLAN assignment. One copy of the received RA is forwarded out the BSSID:

The following packet capture depicts RAs that have been optimised and converted to unicast. The reciever’s destination address in the 802.11 wireless header is replaced with each wireless stations host MAC address participating in the VLAN the RA was received on. The RA is then transmited at each wireless stations unicast transmit data rate. One copy of the received RA is forwarded to each wireless station participating in the VLAN the RA was recieved: