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ccna 200-301 network simulator ns2 download for windows.Preamble Destination Address Destination Address Source Address Length/Type 802.2 Header and Data Frame Check Sequence Frame Check SequenceFigure 3-2.1 Two frame formats1. Ethernet Frame SizeThe original Ethernet standard defined a minimum frame size of 64 bytes and a maximum of 1518 bytes. This included all bytes between the destination MAC address field and the frame checksum sequence field; leading bits and the start frame demarcation field were not included, as can also be calculated from Figure 3.2_1. The maximum frame size allowed was extended to 1522 bytes in the IEEE802.3ac standard released in 1998. The additional 4 bytes in the frame are used to accommodate a new technology, Virtual Local Area Network (VLAN), which is described in the section on switches.If the frame is smaller than 64 bytes or larger than 1522 bytes, it is considered an illegal frame and the illegal frame will be discarded.2. Ethernet MAC Address The MAC address is used to ensure the global uniqueness of an Ethernet device. The IEEE requires any vendor producing Ethernet devices to register and assign a 3-byte vendor code called OrganizationallyUnique Identifier (OUI). IEEE requires vendors to follow two simple rules: all MAC addresses assigned to NICs or other Ethernet devices must use the vendor-assigned OUI for the first 3 bytes: the last 3 bytes are the unique device number produced by each vendor. The MAC address is generally burned into ROM (Read-OnlyMemory) at the time of manufacture, which means that the MAC address cannot be changed, but the display of the MAC address can be changed. When the computer boots up, the NIC copies the address information into memory, which is used to determine whether the received data frame is addressed to the machine, and can be changed by software and the NIC's automatic driver. The display of MAC addresses. When a network device forwards data, the destination MAC address information is added to the frame header. The source device sends the data to the network, and all devices on the network that receive this data look to see if the destination MAC address in the data frame is the same as the local one, and if it is, it is decapsulated and uploaded to the upper layer; if it is not, the frame is discarded.The format of the MAC address may not be the same for different hardware and software manufacturers, but there are about three formats: 00-lbbc-35-ab-40. 0011.bc35.ab4. and 00:ll:bc:35:ab:40o.3. unicast, multicast and broadcastIn Ethernet, Layer 2 uses different MAC addresses: unicast, broadcast, and multicast, as shown in Figure 3-2-2. 00-11-BC-7D-25-04 00-11-BC-7D-25-06 00-11-BC-7D-25-08Figure 3-2-2 Unicast, Broadcast, and Multicast Frames