User`s guide

NetAtlas Enterprise Ethernet Switch Manager User’s Guide
65 Chapter 6 Template
6.4.1 Multicast MAC Address
All Ethernet devices must have a unique MAC address to communicate with one another.
Device such as routers and switches on the LAN keeps a table of MAC-IP address mappings.
When a packet is received, the destination IP address is looked up in the address mapping table
and the packet is forwarded to the intended Ethernet device. IP multicast packets are in the
Class D group addresses, thus an IP multicast address does not correspond to a unique
Ethernet device.
The IANA has reserved a range of address (01:00:5e:00:00:00 to 01:00:5e:7f:ff:ff in
hexadecimal notation) for multicasting. This range gives 23 usable bits. The IP-MAC
multicast address mapping is done by copying the lower-order 23-bit of a Class D address to
the lower-order 23-bit of the MAC multicast address.
The following figure shows an example.
Figure 32 Multicast MAC-IP Address Mapping Example
Since 32 Class D addresses are mapped to the same multicast MAC address, filtering (by
checking the destination IP address) is recommended on the Ethernet devices to reduce
excessive multicast packets.
6.4.2 Static Multicast Group Template Screen
Click Template and then click Static Multicast Group Template to display the screen as
shown.