5-2 IPv4 header :
IP Destination Address
The IP Destination Address field contains a 32-bit binary value that represents the packet destination Network layer host address.
IP Source Address
The IP Source Address field contains a 32-bit binary value that represents the packet source Network layer host address.
Time-to-Live
The Time-to-Live (TTL) is an 8-bit binary value that indicates the remaining "life" of the packet. The TTL value is decreased by at least one each time the packet is processed by a router (that is, each hop). When the value becomes zero, the router discards or drops the packet and it is removed from the network data flow.
Protocol : protocol type used (TCP or Udp)
Type-of-Service
The Type-of-Service field contains an 8-bit binary value that is used to determine the priority of each packet. This value enables a Quality-of-Service (QoS) mechanism to be applied to high priority packets.
Fragment Offset : The fragment offset field identifies the order in which
to place the packet fragment in the reconstruction.
More Fragments flag
The More Fragments flag bit is set, it means that it is not the last fragment of a packet.
IF MF=1 THEN fragment not last, see Fragment Offset to where this fragment is to be placed in the reconstructed packet
IF MF = 0 and fragment offset <>0 THEN it places that fragment as the last part of the reconstructed packet.
An has all zero fragmentation information
IF (MF = 0 and fragment offset =0) THEN unfragmented packet .
Don t Fragment flag
The Don t Fragment (DF) flag is a single bit in the Flag field that indicates that fragmentation of the packet is not allowed. If the Don t Fragment flag bit is set, then fragmentation of this packet is NOT permitted. If a router needs to fragment a packet to allow it to be passed downward to the Data Link layer but the DF bit is set to 1, then the router will discard this packet.
Version - Contains the IP version number (4)
Header Length (IHL) - Specifies the size of the packet header.
Packet Length - This field gives the entire packet size, including header and data, in bytes.
Identification - This field is primarily used for uniquely identifying fragments of an original IP packet
Header Checksum - The checksum field is used for error checking the packet header.
Options - There is provision for additional fields in the IPv4 header to provide other services but these are rarely used.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .