IP header can range from 20 bytes to 60 bytes, out of which 40 bytes is option fields which can be used for network testing and debugging

Some of the common options are:

No operation:

This is of 1 byte and used as a padding options that is making it 4 bytes compatible. It is used as filler between options.

End of Option:

It is also of 1 bytes and is used for padding but at the end of options. It can be used only as the

last option.

Record route:

This is used for storing the routers IP address as the datagram passes through network. It can list upto 9 routers maximum. It can be used for debugging and management purpose.

Strict Source Routing:

This is used to predetermine the route/path of a datagram in the network. A datagram can only route through the one listed in strict source routing. If the datagram is received by any other router, it is discarded.

Loose Source Routing: This is similar to strict loose routing expect the fact that datagram has to pass through the routers listed in the loose source routing but can take different path too.

Timestamp:

This is used to record the time of datagram processed by the router.

Format of IP Options:

Code or type :

Is a 1-byte field specifying the type of IP option that is either record route, strict source routing, loose source routing, no operation and end of options. Each has its code.

For the RR option its value is 7, SSR: 9 and LSR: 3

Len:

It is the total number of bytes of that option or type.

Ptr:

Is called the pointer field. It is a 1-based index into the 39-byte option of where to store the next IP address. Its minimum value is 4, which is the pointer to the first IP address. As each IP address is recorded into the list, the value of ptr becomes 8, 12, 16, up to 36. After the ninth address is recorded ptr becomes 40, indicating the list is full.

Categories: Networking