There are a number of optional parameters that may be present in an Internet Protocol version 4 datagram. They typically configure a number of behaviors such as for the method to be used during source routing, some control and probing facilities and a number of experimental features. Available options

The possible options that can be put in the IPv4 header are as follows: FieldSize (bits)DescriptionCopied1Set to 1 if the options need to be copied into all fragments of a fragmented packet.Option Class2A general options category. 0 is for control options, and 2 is for debugging and measurement. 1 and 3 are reserved.Option Number5Specifies an option.Option Length8Indicates the size of the entire option (including this field). This field may not exist for simple options.Option DataVariableOption-specific data. This field may not exist for simple options. The table below shows the defined options for IPv4. The Option Type column is derived from the Copied, Option Class, and Option Number bits as defined above. Option Type (decimal/hexadecimal)Option NameDescription0/0x00EOOLEnd of Option List1/0x01NOPNo Operation2/0x02SECSecurity (defunct)7/0x07RRRecord Route10/0x0AZSUExperimental Measurement11/0x0BMTUPMTU Probe12/0x0CMTURMTU Reply15/0x0FENCODEENCODE25/0x19QSQuick-Start30/0x1EEXPRFC3692-style Experiment68/0x44TSTime Stamp82/0x52TRTraceroute94/0x5EEXPRFC3692-style Experiment130/0x82SECSecurity (RIPSO)131/0x83LSRRLoose Source & Record Route 133/0x85E-SECExtended Security (RIPSO)134/0x86CIPSOCommercial IP Security Option136/0x88SIDStream ID137/0x89SSRRStrict Source & Record Route142/0x8EVISAExperimental Access Control144/0x90IMITDIMI Traffic Descriptor145/0x91EIPExtended Internet Protocol147/0x93ADDEXTAddress Extension148/0x94RTRALTRouter Alert149/0x95SDBSelective Directed Broadcast151/0x97DPSDynamic Packet State152/0x98UMPUpstream Multicast Packet158/0x9EEXPRFC3692-style Experiment205/0xCDFINNExperimental Flow Control222/0xDEEXPRFC3692-style Experiment

Loose source routing

Loose Source & Record Route (LSRR) is an IP option which can be used for address translation. LSRR is also used to implement mobility in IP networks.

Loose source routing uses a source routing option in IP to record the set of routers a packet must visit. The destination of the packet is replaced with the next router the packet must visit. By setting the forwarding agent (FA) to one of the routers that the packet must visit, LSR is equivalent to tunneling. If the corresponding node stores the LSR options and reverses it, it is equivalent to the functionality in mobile IPv6.

The name loose source routing comes from the fact that only part of the path is set in advance.

Strict source routing

Strict Source and Record Route (SSRR) is in contrast with loose source routing, in which every step of the route is decided in advance where the packet is sent.

Restrictions and considerations The following two options are discouraged because they create security concerns: Loose Source and Record Route (LSRR) and Strict Source and Record Route (SSRR). Many routers block packets containing these options.

See also

Dynamic Source Routing Source routing Internet Protocol

References