Figure 387 Ip V4 Packet Headers; Table 160 Ip V4 Packet Headers - ZyXEL Communications 200 Series User Manual

Figure 387 IP v4 Packet Headers

The header fields are discussed below:

Table 160 IP v4 Packet Headers

HEADER
Version
IHL
Type of Service
Total Length
Identification
Flags
Fragment Offset
Time To Live
Protocol
Header Checksum
Source IP Address
Destination IP Address
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DESCRIPTION
The value 4 indicates IP version 4.
IP Header Length is the number of 32 bit words forming the total
length of the header (usually five).
The Type of Service, (also known as Differentiated Services Code
Point (DSCP)) is usually set to 0, but may indicate particular quality
of service needs from the network.
This is the size of the datagram in bytes. It is the combined length
of the header and the data.
This is a 16-bit number, which together with the source address,
uniquely identifies this packet. It is used during reassembly of
fragmented datagrams.
Flags are used to control whether routers are allowed to fragment
a packet and to indicate the parts of a packet to the receiver.
This is a byte count from the start of the original sent packet.
This is a counter that decrements every time it passes through a
router. When it reaches zero, the datagram is discarded. It is used
to prevent accidental routing loops.
The protocol indicates the type of transport packet being carried,
for example, 1 = ICMP; 2= IGMP; 6 = TCP; 17= UDP.
This is used to detect processing errors introduced into the packet
inside a router or bridge where the packet is not protected by a link
layer cyclic redundancy check. Packets with an invalid checksum
are discarded by all nodes in an IP network.
This is the IP address of the original sender of the packet.
This is the IP address of the final destination of the packet.
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