Protocol specification
- Standard formulation
- Provided service access points and service access points requested by the next layer
- Provided functions
- Internal structure of protocol data unit
- Timing of data packets
- RFC [request for comment, a standard proposed by an individual or organization that hopes to be widely used, needs to be reviewed before it can become a standard] to the standard
Addresses of different protocol layers
- Protocol layer address and function
- Assignment of each protocol layer address
- Hardware address [assigned by hardware provider]
- IP address [assigned by IP address authority]
- Application address [port number] allocation [There are several methods, one is to use a port number that everyone knows, such as WEB port number 80]
- Host name address allocation [assigned by a set of registered official institutions, matched with IP addresses through DNS protocol]
- Dynamic address and static address
- The dynamic address is obtained when the system is started or assigned by a third party, and it can be changed
- The static address is set during the initial configuration of the computer system and is unchanged unless it is changed manually
Protocol header
- Classification of the head
- Fixed packet type
- Unlimited packet type
- The composition of the fixed head
- Fixed part [contains information that needs to be processed for each data packet, such as address and control information]
- Optional part [usually used as part of the first few data packets to coordinate a set of parameters required for communication]
- Basic structure of PDU [Control data packet does not contain payload]
- Unlimited header [The size and format of the domain are not fixed] [It often appears in the application layer]
Analysis of sample questions [used as an exam, not necessarily the correct answer]
- What happens if two computers have the same IP address?
If two computers are on the same network, then when sending a data packet, it may not be one computer each time;
if the two computers are on different networks, then the destination IP address in a certain network is determined by the routing table The hardware address will be unique, so there will be no error - What happens if two computers have the same Ethernet address [physical address]?
If they are on the same network, no matter which one is in the network, the sender will get multiple responses when sending a data packet, which will cause the protocol to fail.
If they are on different networks, there is no problem, because Ethernet Address is applied locally