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2025-02-16 09:46 本頁面
【正文】 a message sent to this address is broadcast to each machine on the sub. ? – send to “all nodes” on work ? Limited Broadcast ? Network ID and/or Host ID Cannot Be All Bits Set to 0 ? used by Cisco routers to designate the default route ? 0 means “this work or segment”, or “this node” ? Host ID Must Be Unique to the Network Assigning Network Addresses Router 1 2 3 Router Assigning Host Addresses Router Router 1 2 3 Subting What is a Sub? Why Subting? Implementing Subting Sub Masks Default Sub Masks Possible Sub Masks for Class A, B C Defining a Sub Mask Defining a Sub IDs Defining a Host Ids Example 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. 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 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. What is a Sub? (4) After Sub Network ID Sub Mask Host Range ………… …………. TOTAL 254 SUBNETS 254 HOSTS PER SUBNET 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 expensive。 connecting multiple smaller works makes the system more efficient Implementing Subting ? Determine the Number of Required Network IDs ? One for each sub ? One for each widearea work connection ? Determine the Number of Required Host IDs per Sub ? One for each TCP/IP host ? One for each router interface ? Based on the above requirement, create the following: ? Define One Sub Mask Based on Requiremen
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