Option Class

Option Number

Length (bytes)

Option Name

Description

0

0

1

End Of Options List

An option containing just a single zero byte, used to mark the end of a list of options.

0

1

1

No Operation

A “dummy option” used as “internal padding” to align certain options on a 32-bit boundary when required.

0

2

11

Security

An option provided for the military to indicate the security classification of IP datagrams.

0

3

Variable

Loose Source Route

One of two options for source routing of IP datagrams. See below for an explanation.

0

7

Variable

Record Route

This option allows the route used by a datagram to be recorded within the header for the datagram itself. If a source device sends a datagram with this option in it, each router that “handles” the datagram adds its IP address to this option. The recipient can then extract the list of IP addresses to see the route taken by the datagram.

Note that the length of this option is set by the originating device. It cannot be enlarged as the datagram is routed, and if it “fills up” before it arrives at its destination, only a partial route will be recorded.

0

9

Variable

Strict Source Route

One of two options for source routing of IP datagrams. See below for an explanation.

2

4

Variable

Timestamp

This option is similar to the Record Route option. However, instead of each device that handles the datagram inserting its IP address into the option, it puts in a timestamp, so the recipient can see how long it took for the datagram to travel between routers.

As with the Record Route option, the length of this option is set by the originating device and cannot be enlarged by intermediate devices.

2

18

12

Traceroute

Used in the enhanced implementation of the traceroute utility, as described in RFC 1393. Also see the topic on the ICMP Traceroute messages.