- Two services provided by the network layer
- Internet Protocol IP
- Intermediate equipment
① Intermediate device for physical layer: transponder
② Data Link layer: Bridge
③ Network layer: Routers
④ Network layer above: Gateway
When the intermediate device is a transponder or a bridge, it just expands the Ethernet. Network interconnection: Routers make network interconnection and routing choices.
- Classification of IP addresses
- IP address and how it is represented
- IP address: Give each host or interface on the Internet a unique 32 identifier worldwide.
- Classified IP Address: The IP address is divided into a fixed number of classes, each class has two fixed length fields, one is the network number-flag host connected to the network, a network number in the entire network must be unique; one is the host number-flag the host, the host number must be unique within its network number ; So the IP address is unique.
IP address = = (Network number, host number)
- Class A address: The first byte is fixed 0, the network number can be assigned is 126 (2 of 7 square-2), the full 0 and all 1 minus (00000000,01111111), a class address of the host number = = (2 24 of the Square 2), full 0 and full 1. A Class A address has 2 of the 31-second address.
Class B Address: The first two bytes fixed 10, can be assigned network number ==2 14 -1;b class address the maximum number of hosts ==2 16 square-2;
Class C Address: The first three bytes fixed 110, the following 21 bits can be assigned, the network number can be assigned to ==2 21 -1;c class address the maximum number of hosts ==2 8-2
- Features of IP address:
①: Routers only forward groupings based on the network number to which the destination host is connected, regardless of the host number.
②: A network is a collection of hosts with the same network number as the Net-id, so a number of LANs connected to the hub and bridge are still a network.
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- IP address and hardware address
- is the address used by the data link layer and the physical layer, and the IP address is the address used by the network layer and the above layers, and is a logical address
IP address is placed in IP datagram header, and the hardware address is placed on the Mac frame header, the network layer and the network layer above the use of IP address, and the data link layer and the following use of MAC address. After the IP datagram is placed in the Mac frame of the data link layer, the entire IP datagram becomes the data of the Mac frame, so the data link layer cannot see the IP address of the datagram.
- Address Resolution Protocol ARP
- IP layer Forwarding group process
- Constructing subnets and networks
- Subnet mask: Used to solve a datagram reached the router R1, but do not know how to forward it to the subnet. The subnet mask can solve this problem. The subnet mask and the IP address of the datagram are bitwise, and the result is the network address of the subnet.
The subnet mask is represented by a series of 1 and 0.
- Regardless of the mesh, you have to use a subnet mask, so that it is convenient to obtain the IP address of the network address, and do not need to find the routing table.
- A subnet mask is an important property of a network or a subnet. In each item of the router's routing table, in addition to giving the destination network address, you must also give the subnet mask for the network. If a router is connected to two subnets, two IP addresses and subnet masks are given 、、。
- Forwarding by using subnet time group
- No classification addressing
- Routing between non-categorical domains CIDR
- Characteristics
① eliminates the A,b,c class address and the concept of subnetting. He divides the 32-bit IP address into two parts. The preceding is the network prefix, which is followed to indicate the host. A diagonal method is also used.
- The back of the slightly
Computer networks--Network layer
