‫So looking at an IP packet consisting of a header section and a data section.
‫We'll see that the IPv4 packet header consists of 14 fields and only the options field is, well, optional.
‫Now I'm not going to talk about each field one by one, but I'll give you a few short explanations of
‫some of the more pertinent ones.
‫The version field is always equal to four.
‫Why IPV four?
‫The Internet header length IHF field is the size of the header in words where word is always going to
‫be 32 bits.
‫The total length is the entire package size in this case, it's in bytes, as you know, but to get
‫you up to speed, one bite is a bit.
‫The minimum size is 20 bytes, so that's a header without data and the maximum is 65000 535 bytes.
‫The flag is used to determine the fragmentation options.
‫Bit one is the A4 don't fragment if it's set.
‫And I mean by that, if this bit is one and fragmentation is required to route the packet, then the
‫packet is dropped.
‫Bit too is M.F. or more fragment.
‫For fragmented package, all fragments, except the last have the IMF flag set.
‫Net zero is reserved for the future.
‫Title or time to live.
‫Is to limit the lifetime of a packet.
‫It's a hot count, basically, when the packet arrives at a router, the router decrements the total
‫field by one.
‫Protocol field is the protocol used in the data portion of the IP packet.
‫So that's going to be TCP, udp, ICMP.
‫Source address and destination address fields are the most important fields of an IP header.
‫These fields are the IPv4 address of the sender of the packet and the IPv4 address of the receiver of
‫the packet.
‫Please note that this address may be changed in transit by a network address translation device.
‫We'll talk about that later.
‫This is how an IPv4 packet is seen on Wireshark.
‫So it's a DNS query response.
‫The fields we mentioned are seen pretty clearly.
‫Versions for.
‫Header length is five words, which means no options field.
‫Go to length is 96 bytes.
‫Mfe and deer flags are not set.
‫And you can see the source and the destination addresses and all the rest.