680| IP Mobility AOS-W 6.5.3.x| User Guide
6. Roaming is complete.
Enabling Mobility Multicast
Internet Protocol (IP) multicast is a network addressing method used to simultaneously deliver a single stream
of information from one sender to multiple clients on a network. Unlike broadcast traffic, which is meant for all
hosts in a single domain, multicast traffic is sent only to those specific hosts who are configured to receive such
traffic. Clients who want to receive multicast traffic can join a multicast group via IGMP messages. Upstream
routers use IGMP message information to compute multicast routing tables and determine the outgoing
interfaces for each multicast group stream.
In AOS-W 3.3.x and earlier, when a mobile client moved away from its local network and associated with a
VLAN on a foreign switch (or a foreign VLAN on its own switch), the client’s multicast membership information
would not be available at its new destination, and multicast traffic from the client could be interrupted. AOS-W
3.4 and later supports mobility multicast enhancements that provide uninterrupted streaming of multicast
traffic, regardless of a client's location.
Working with Proxy IGMP and Proxy Remote Subscription
The switch is always aware of the client's location, so the switch can join multicast group(s) on behalf of that
mobile client. This feature, called Proxy IGMP, allows the switch to join a multicast group and suppresses the
client’s IGMP control messages to the upstream multicast router. (The client's IGMP control messages will,
however, still be used by switch to maintain a multicast forwarding table.) The multicast IGMP traffic
originating from the client will instead be sent from the switch’s incoming VLAN interface IP.
The IGMP proxy feature includes both a host implementation and a router implementation. An upstream
router sees a switch running IGMP proxy as a host; a client attached to the switch sees the switch as router.
When you enable Proxy IGMP, all multicast clients associated with the switch are hidden from the upstream
multicast device or router.
The newer IGMP proxy feature and the older IGMP snooping feature cannot be enabled at the same time, as both
features add membership information to multicast group table. For most multicast deployments, you should enable
the IGMP Proxy feature on all VLAN interfaces to manage all the multicast membership requirements on the switch.
If IGMP snooping is configured on some interfaces, there is a greater chance that multicast information transfers
may be interrupted.
IGMP proxy must be enabled or disabled on each individual interface. To use the IGMP proxy, ensure that the
VLANs on the switches are extended to the upstream router. Enabling IGMP proxy enables IGMP on the
interface and sets the querier to the switch itself. You must identify the switch port from which the switch
sends proxy join information to the upstream router, and identify the upstream router by upstream port so
the switch can dynamically update the upstream multicast router information.
IGMPv3 Support
AOS-W 6.4 supports IGMPv3 functionality that makes Alcatel-Lucent switches aware of the Source Specific
Multicast (SSM) and is used to optimize bandwidth of the network. The SSM functionality is an extension of IP
multicast where the datagram traffic is forwarded to receivers from only those multicast sources to which the
receivers have explicitly joined. By default, the multicast group range of 232.0.0.0 through 232.255.255.255
(232/8) is reserved for SSM by IANA (Internet Assigned Numbers Authority).
The IGMPv3 snooping functionality is configured at the edge of the network. The devices that support IGMP
snooping listen for the IGMP messages that the host sent to join an IP multicast group. These devices record
details of all the hosts and also about the IP multicast group in which a particular host has joined. These devices
forward IP multicast traffic to the hosts that have joined the specific multicast group.
To Next Page
Loading...