![]() ![]() Options : This optional, variable length field is used primarilt for testing and troubleshooting.04:32:08 Pre-allocating up to position 0x400000 in rev00253.dat Destination IP Address : This field specifies the 32-bit IP address of the destination of the IP packet. Source IP Address : This field sepecifies the 32-bit IP address of the originator of the IP packet. Each router must recalculate the checksum and update the field before forwarding the IP packet. Remember that each router decrements the TTL field by 1 and packet fragmentation is also possible. At each hop, the router calculates the IP header checksum and verifies it with the value in the IP header. Header Checksum : This 16-bit field is used for error correction for just the IP header. Examples of protocol numbers are 6 for TCP, 17 for UDP, and 1 for ICMP. Protocol : This 8-bit field specifies the number of the Layer 4 protocol used in the data portion of the packet. WHen the TTL field reaches zero, the router discards the packet and sends an error message to the sending device. Each router that a packet crosses decrements (減量) the TTL field by one. TTL (Time to Live) : Used to prevent packets from persisting indefinitely on a network, this 8-bit field is set to a number, commonly 64, when the packet is created. Fragment Offset : This 13-bit field specifies the offset, in units of 8 octets, of a particular fragment relative to the beginning of the original un-fragmented IP datagram. Flags : This 3-bit field is used to control or identify fragments. Identification : Used together with the Flags and Fragment Offset fields, this 16-bit field is primarily used for uniquely identifying fragments of an original IP datagram. Total Length : This 16-bit field specifies the entire packet size in octets, including both header and data. In other words, the DiffServ byte can be used for traffic prioritization where devices support it. The DiffServ (Differentiated Service) byte can be used as a method of adding QoS (Quality of Service) to IP networks. DiffServ (formerly ToS) : This 8-bit field was originally called the Type of Service, or simply the TOS byte. The length is in terms of 32-bit words, so the actual Options field value range is from five 32-bit words to six 32-bit words. The IP header length can range from 20 to 24 octets. Because the Options field can vary in length, the receiver needs to know how long the header is. IP Header Length : As the name implies, this 4-bit field indicates the length of the IP header. ![]() For IPv4, this field has a value of 4 for IPv6, this filed has a value of 6. Version : This is a 4-bit field identifying the IP version. Notice that the source and destination IP addresses are just two of the fields in the header and they actually appear near the end of the header. When a computer needs to send data, the Internet Layer adds an IP header to the data to form an IP packet. (Deadline:2400)Ģ.Make some notes what I’ve understood from the video. **Sum of job:** I know the background knowledge of IP.ġ.Watch first-2 part of the fourth video. **WHAT do I want to do?** Having eLearning with several videos. **WHY do I do this job?** Beacuse I need to understand what is all about IP. =IP Addressing (background knowledge of IP)= ![]()
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