Internet Protocol Options

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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. [1]

Contents

Available options

The possible options that can be put in the IPv4 header are as follows:

FieldSize (bits)Description
Copied1Set 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. [2]

Option Type (decimal/hexadecimal)Option NameDescription
0/0x00EOOLEnd of Option List
1/0x01NOPNo Operation
2/0x02SECSecurity (defunct)
7/0x07RRRecord Route
10/0x0AZSUExperimental Measurement
11/0x0BMTUPMTU Probe
12/0x0CMTURMTU Reply
15/0x0FENCODEENCODE
25/0x19QSQuick-Start
30/0x1EEXPRFC3692-style Experiment
68/0x44TSTime Stamp
82/0x52TRTraceroute
94/0x5EEXPRFC3692-style Experiment
130/0x82SECSecurity (RIPSO)
131/0x83LSRLoose Source Route
133/0x85E-SECExtended Security (RIPSO)
134/0x86CIPSOCommercial IP Security Option
136/0x88SIDStream ID
137/0x89SSRStrict Source Route
142/0x8EVISAExperimental Access Control
144/0x90IMITDIMI Traffic Descriptor
145/0x91EIPExtended Internet Protocol
147/0x93ADDEXTAddress Extension
148/0x94RTRALTRouter Alert
149/0x95SDBSelective Directed Broadcast
151/0x97DPSDynamic Packet State
152/0x98UMPUpstream Multicast Packet
158/0x9EEXPRFC3692-style Experiment
205/0xCDFINNExperimental Flow Control
222/0xDEEXPRFC3692-style Experiment

Loose source routing

Loose Source Routing is an IP option which can be used for address translation. LSR is also used to implement mobility in IP networks. [3]

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. [4]

Strict source routing

Strict source routing 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. [5]

See also

References

  1. "Internet Protocol Version 4 (IPv4) Parameters" . Retrieved 2018-08-07.
  2. "Internet Protocol Version 4 (IPv4) Parameters".
  3. Bhagwat, Pravin; Perkins, Charles Edward; Tripathi, Satish (July 1996). "Network Layer Mobility:An Architecture and Survey". IEEE Personal Communications . 3 (3): 54–64. doi:10.1109/98.511765. hdl: 1903/780 . Retrieved 2024-01-30.
  4. "Source Routing". Archived from the original on 2008-02-24. Retrieved 2008-02-10.
  5. "Cisco unofficial FAQ" . Retrieved 2012-05-10.