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ccna certification germany.Options (optional, variable length) PaddingFigure 2.3 IPv4 packet header formatVersion (4 bits): Used to determine the version of the IP packet, this field is always set to 0100 for IPv4 packets and 0110 for IPv6 packets. packet header length (4 bits): Used to determine the length of the packet header, this value multiplied by 4 is the length of the packet header in bytes. The minimum value for this field is 5 (20 bytes) and the maximum value is 15 (60 bytes).Differentiated Service (8 bits): formerly known as the Type ofService (ToS) field, used to determine the IPv4 priority of each packet, the first 6 bits are used to determine the Differentiated Services Code Point (DSCP) value used by the Quality of Service (QoS) mechanism, and the last 2 bits are used to determine the Explicit CongestionNotification (ECN) value, which can be used to prevent packets from being dropped during network congestion. Point (DSCP) value used by the Quality of Service (QoS) mechanism, and the last 2 bits are used to determine the Explicit CongestionNotification (ECN) value, which can be used to prevent packets from being dropped in case of network congestion.Total length (16 bits): defines the entire packet size, including the sum of the packet header and data portion lengths, in bytes.Identifier (16 bits): uniquely identifies the data slice of the original IPv4 packet.Flags (3 bits): identifies how the packet was segmented, which, along with the segment offset and identification fields, helps reorganize the segmented data into the original packet.Segment Offset (13 bits): identifies the order in which packet segments were placed in the original unsegmented packet reassembly.TimeToLive (8 bits): Used to limit the packet lifetime, the sender of the packet sets the initial TimeToLive (TTL) value and the TTL value is reduced by 1 for each routing device the packet passes through. if the value of the TTL field is reduced to zero, the router drops the packet and sends an ICMP (InternetControlMessage Protocol) timeout message to the source IPv4 address. InternetControlMessage Protocol) timeout message to the source IPv4 address..12 . Cisco Networking Lab CCNA Lab Guide (Release 2).