Earlier versions of Network Load Balancing in Multicast
mode use the concept of a unicast IP address that is mapped to a multicast
media access control address. Because a switch is unable to associate this
multicast media access control address to a specific switch port, packets that
are sent to this multicast media access control address are flooded across all
switch ports, which may be undesirable in some cases. In Windows Server 2003, a
Network Load Balancing cluster can also take part in a multicast
group.
You must first enable IGMP snooping on the switch and you must
make sure to connect each cluster node's virtual adapter to a unique switch
port. When you select the IGMP option within the Network Load Balancing
properties, each Network Load Balancing cluster node periodically sends an IGMP
Join message that indicates the multicast group of which it is a member. Upon
receiving these Join messages, the switch can associate the ports that have a
Network Load Balancing cluster host attached to the multicast group. Incoming
packets that are destined to the multicast media access control address are
then passed only to those ports that have an attached Network Load Balancing
cluster node.
The address range of the multicast group that is used
is 239.255.
x.
y, where
x.
y corresponds to the
last two octets of the Network Load Balancing virtual IP address. For example,
if the virtual IP address is 10.1.2.3, the multicast address that cluster nodes
are a part of would be 239.255.2.3. Per the RFC document 2365, this address
range is administratively scoped, which means that any IGMP Join messages sent
to an address in this range are not forwarded by border gateway routers. This
prevents interference with any traffic on the Internet.
For additional information, click the following article number
to view the article in the Microsoft Knowledge Base:
323437
HOW TO: Configure Network Load Balancing Parameters in Windows Server 2003