WSM Reference Guide - WatchGuard Technologies

CHAPTER 1Internet Protocol ReferenceInternet Protocol (IP) sets the format of packets and the address pattern for sending data through theInternet. It operates as a postal system, and allows you to address a package and drop it into the system.But, there is no direct link between you and the recipient. In other words, there is no package.Most networks mix IP with higher level protocols such as Transmission Control Protocol (TCP). TCP/IPmakes a connection between two host servers. Then, they can send messages to each other. TCP/IP suppliesthe “packaging.”Internet Protocol HeaderInternet Protocol (IP) is an Internet standard that enables the sending of datagrams — packets of informationthat include an address and instructions on how to send the datagram to its destination. IPprepends a header to each datagram. The IP header contains a minimum of 12 properties, and otheroptional properties.Property Size DescriptionVersion 4 bits IP format number (Current version = 4)IHL 4 bits Header length in 32-bit words (Minimum = 5)TOS 8 bits Type of service sets routing priorities. It is usually not usedbecause not many application layers can set it.Tot_Len 16 bits Total length of packet measured in octets. It is used to assemblefragments.ID 16 bits Packet ID, used to assemble fragments.Flags 3 bits Miscellaneous flagsFrag_Off 13 bits Identifies fragment part for this packet.TTL 8 bits Time to live. It sets the maximum time the datagram remainsalive in the system.Protocol 8 bits IP protocol number. Indicates which of TCP, UDP, ICMP, IGMP, orother Transport protocol is inside.Reference Guide 1