IP datagram of datagram, how ip datagram is changing

IP Datagram: The protocol unit in which the IP protocol controls the transmission.

What inevitably changes is the time to live (TTL) and the first checksum. For each hop router, the TTL value is reduced by one; The header checksum is generated based on the header, and if the TTL field changes, the header checksum will change accordingly. Possible variations are flags, slice offsets, and datagram total lengths.

When the data fiber of host A to host B is encapsulated into IP packets at the network layer, the header of the IP packet contains the source and destination addresses. Host A uses the 24-bit IP netmask configured by the local machine to perform calculations with the destination address to determine whether the destination network address and the local network address are in the same network segment. If not, the IP packet is sent to the gateway.

What inevitably changes is the time to live (TTL) and the first checksum. Each fiber line hop router passes through, the TTL value.

minus one; The header checksum is generated based on the header, and if the TTL field changes, the header checksum will change accordingly. Possible variations are flags, slice offsets, and datagram total lengths.

When host A sends traffic to host B.

At the network layer, IP packets are encapsulated, and the header of the IP packets contains the source and destination addresses. Host A uses the natively configured 24-bit IP netmask.

and the target address.

Determine whether the destination network address and the local network address are in the same network segment. If not, the IP packet is sent to the gateway.

We can think of IP datagrams as fragments by 4betys.

First of all, the first paragraph of 4betys has a total of 32 bits, the protocol version accounts for 4 bits, and the length of the head accounts for 4 bits, instead of the number that you said the bit can represent is 0 15, and its unit is 32 bits (4bytes), so it is not 15 bytes, but 0 15 * 4 (60) bytes, and because the length of the fixed part of the head is 20bytes, the minimum length of the header is 20 bytes, and the maximum is 60 bytes. Then there are 8 bits for the discriminating service, and then 16 bits for the total length (not 16 bytes), which is the representation range of 0 65535, so the maximum length of the datagram is 65535 bytes.

The second paragraph includes logos, signs, and sheet offsets. The third paragraph includes the time to live, the protocol, the first test, and the . The fourth segment is the source address. The fifth paragraph is the destination address.

We can see that the above 5 segments, each 32 bits (4 bytes) are some control information necessary to send data, so every IP data should have, so the above 5 segments are used as a fixed part, a total of 5*4 (20 bytes), which is the reason why the first part is fixed with a minimum of 20 bytes.