![]() Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site. In Figure 7-13, the destination MAC address and destination IP address are both multicast addresses. The multicast MAC address is associated with, and uses addressing information from, the IPv4 or IPv6 multicast address. The source is always a unicast address.Īs with the unicast and broadcast addresses, a multicast IP address requires a corresponding multicast MAC address to deliver frames on a local network. Because a multicast address represents a group of addresses (sometimes called a host group), it can only be used as the destination of a packet. ![]() The range of IPv6 multicast addresses begins with ff00::/8. If the encapsulated data is an IP multicast packet, the devices that belong to a multicast group are assigned a multicast group IP address. It is not forwarded by a router unless the router is configured to route multicast packets. It is flooded out all Ethernet switch ports except the incoming port, unless the switch is configured for multicast snooping. There are other reserved multicast destination MAC addresses for when the encapsulated data is not IP, such as Spanning Tree Protocol (STP) and Link Layer Discovery Protocol (LLDP). It has destination MAC address 01-00-5E when the encapsulated data is an IPv4 multicast packet and destination MAC address 33-33 when the encapsulated data is an IPv6 multicast packet. The features of an Ethernet multicast frame are as follows: Multicast MAC Address (7.2.6)Īn Ethernet multicast frame is received and processed by a group of devices on the Ethernet LAN that belong to the same multicast group. For example, ARP requests do not use IPv4, but the ARP message is sent as an Ethernet broadcast. However, not all Ethernet broadcasts carry IPv4 broadcast packets. When the IPv4 broadcast packet is encapsulated in the Ethernet frame, the destination MAC address is the broadcast MAC address FF-FF-FF-FF-FF-FF in hexadecimal (or 48 1s in binary).ĭHCP for IPv4 is an example of a protocol that uses Ethernet and IPv4 broadcast addresses. The IPv4 destination address is a broadcast address, 192.168.1.255. The source host sends an IPv4 broadcast packet to all devices on its network. This means that the address is permanently encoded into the ROM chip. Sometimes a MAC address is referred to as a burned-in address (BIA) because the address is hard coded into read-only memory (ROM) on the NIC. In such a case, it is necessary to modify the MAC address with a new NIC or make modifications by using software. ![]() However, it is possible for duplicate MAC addresses to exist because of mistakes made during manufacturing, mistakes made in some virtual machine implementation methods, or modifications made using one of several software tools. It is the responsibility of a vendor to ensure that no two of its devices are assigned the same MAC address. Therefore, the Ethernet MAC address of that device would be 00-60-2F-3A-07-BC. Cisco would configure the device with a unique vendor code such as 3A-07-BC. Because 1 byte equals 8 bits, we can also say that a MAC address is 6 bytes in length.įigure 7-8 The Ethernet MAC Address Structureįor example, say that Cisco needs to assign a unique MAC address to a new device, and the IEEE has assigned Cisco the OUI 00-60-2F. MAC addressing provides a method for device identification at the data link layer of the OSI model.Īn Ethernet MAC address is a 48-bit address expressed using 12 hexadecimal digits, as shown in Figure 7-7. The MAC address is used to identify the physical source and destination devices (NICs) on the local network segment. ![]() In an Ethernet LAN, every network device is connected to the same shared medium. If such conversions are required, convert the decimal or hexadecimal value to binary and then to convert the binary value to either decimal or hexadecimal as appropriate. You might have to convert between decimal and hexadecimal values. Hexadecimal may also be represented using a subscript 16 or by using the hex number followed by an H (for example, 73H). Hexadecimal numbers are often represented by a value preceded by 0x (for example, 0x73) to distinguish between decimal and hexadecimal values in documentation. For example, in Figure 7-6, the binary value 0000 1010 is shown to be 0A in hexadecimal. When using hexadecimal, leading zeros are always displayed to complete the 8-bit representation. Figure 7-6 Selected Examples of Decimal to Binary to Hexadecimal Conversions
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