【正文】 ecimal format (dotted decimal notation). 來自 Network Addressing *The class of the Network is determined by the high order bits *Class D is for Multicast and Class E is reserved for Research. Class C Class A Network Address Host Address 0 Class B Network Address Host Address 1 0 Network Address Host Address 1 1 0 0000 0000 0000 0001 1 .. 0111 1110 126 0111 1111 127 1000 0000 128 1011 1111 191 1100 0000 192 1101 1111 223 來自 Address Class Summary Number of Networks 126 16,384 2,097,152 Number of Hosts per Network 16,777,214 65,534 254 Class A Class B Class C Range of Network IDs (First Octet) 1 – 126 128 – 191 192 – 223 來自 Network Addresses: Special Purpose and Guidelines ? Network Address Cannot Be 127 ? 127 is reserved for loopback functions and selfdiagnostic ? is reserved as a loopback address ? Network ID and/or Host ID Cannot Be All Bits Set to 1 ? All 1s means “All works”, or “all nodes” ? 255 is a broadcast address。 C Defining a Sub Mask Defining a Sub IDs Defining a Host Ids Example 來自 What is a Sub? (1) Sub 1 Sub 2 Main Network A sub is a subsection of an work, defined for administrative purpose or to cut down on broadcast traffic, as all messages on a work are “heard” by all hosts whether the message is for that host or not. Message sent from one host to another within the same sub do not need to be routed, but messages sent between hosts in different subs must be routed. Subs are connected by routers, or default gateways. 來自 What is a Sub? (2) Network ID Host ID 1 0 Example Network ID FROM ISP No. of Network = 1 SUBNET MASK No. of Hosts = 65534 (2^162) Network ID Host ID 1 0 We need more works Sub ID Borrow from Host ID 來自 What is a Sub? (3) After Sub Network ID bee Sub mask bee No. of Subs 254 Host for per Sub 254 (2^82) Network ID Host ID 1 0 Sub ID Use all 8 bit 11111111 for Sub 254 binations (2^82)* Only 8 bit for Host * However, according to RFC 1812, 255 binations can be achieved. 來自 What is a Sub? (4) After Sub Network ID Sub Mask Host Range ………… …………. TOTAL 254 SUBNETS 254 HOSTS PER SUBNET 來自 Why Subting? ? Reduced work traffic – ? smaller the work smaller the broadcast domains and less work traffic on that work segment ? Optimized work performance – ? result of reduced work traffic ? Simplified management – ? easier to identify and isolate work problems in a smaller group ? Facilitated spanning of large geographical distances – ? since WAN links are considerably slower and more expensi