IPSec, Internet Protocol Security protocol suite

Description Glossary RFCs Publications Obsolete RFCs


Protocol suite: TCP/IP.
Working groups: bmwg, Benchmarking Methodology.
btns, Better-Than-Nothing Security.
ipsec, Internet Protocol Security.
ipsecme, IP Security Maintenance and Extensions.
ipsp, IP Security Policy.
mip6, Mobility for IPv6.
Links: www.strongswan.org 

RFC 2401:

IPsec is designed to provide interoperable, high quality, cryptographically-based security for IPv4 and IPv6. The set of security services offered includes access control, connectionless integrity, data origin authentication, protection against replays (a form of partial sequence integrity), confidentiality (encryption), and limited traffic flow confidentiality. These services are provided at the IP layer, offering protection for IP and/or upper layer protocols.

These objectives are met through the use of two traffic security protocols, the Authentication Header (AH) and the Encapsulating Security Payload (ESP), and through the use of cryptographic key management procedures and protocols. The set of IPsec protocols employed in any context, and the ways in which they are employed, will be determined by the security and system requirements of users, applications, and/or sites/organizations.

When these mechanisms are correctly implemented and deployed, they ought not to adversely affect users, hosts, and other Internet components that do not employ these security mechanisms for protection of their traffic. These mechanisms also are designed to be algorithm-independent. This modularity permits selection of different sets of algorithms without affecting the other parts of the implementation. For example, different user communities may select different sets of algorithms (creating cliques) if required.

A standard set of default algorithms is specified to facilitate interoperability in the global Internet. The use of these algorithms, in conjunction with IPsec traffic protection and key management protocols, is intended to permit system and application developers to deploy high quality, Internet layer, cryptographic security technology.

Transport layer protocols:

AH, IP Authentication Header.

ESP, Encapsulating Security Payload.

Application layer protocols:

GDOI, Group Domain of Interpretation.

IKE, Internet Key Exchange.

ISAKMP, Internet Security Association and Key Management Protocol.


Access Control.
(RFC 2401) Access control is a security service that prevents unauthorized use of a resource, including the prevention of use of a resource in an unauthorized manner. In the IPsec context, the resource to which access is being controlled is often: for a host, computing cycles or data for a security gateway, a network behind the gateway or bandwidth on that network.



(RFC 2401) Confidentiality is the security service that protects data from unauthorized disclosure. The primary confidentiality concern in most instances is unauthorized disclosure of application level data, but disclosure of the external characteristics of communication also can be a concern in some circumstances. Traffic flow confidentiality is the service that addresses this latter concern by concealing source and destination addresses, message length, or frequency of communication. In the IPsec context, using ESP in tunnel mode, especially at a security gateway, can provide some level of traffic flow confidentiality.

(RFC 2401) A security mechanism used to transform data from an intelligible form (plaintext) into an unintelligible form (ciphertext), to provide confidentiality. The inverse transformation process is designated decryption. Oftimes this term is used to generically refer to both processes.

Data Origin Authentication.
(RFC 2401) A security service that verifies the identity of the claimed source of data. This service is usually bundled with connectionless integrity service.

DOI, Domain Of Interpretation.

(RFC 2401) Integrity is a security service that ensures that modifications to data are detectable. Integrity comes in various flavors to match application requirements. IPsec supports two forms of integrity: connectionless and a form of partial sequence integrity. Connectionless integrity is a service that detects modification of an individual IP datagram, without regard to the ordering of the datagram in a stream of traffic. The form of partial sequence integrity offered in IPsec is referred to as anti-replay integrity, and it detects arrival of duplicate IP datagrams (within a constrained window). This is in contrast to connection-oriented integrity, which imposes more stringent sequencing requirements on traffic, e.g., to be able to detect lost or re-ordered messages. Although authentication and integrity services often are cited separately, in practice they are intimately connected and almost always offered in tandem.


SA, Security Association.
(RFC 2401) A simplex (uni-directional) logical connection, created for security purposes. All traffic traversing an SA is provided the same security processing. In IPsec, an SA is an internet layer abstraction implemented through the use of AH or ESP.

Security Gateway.
(RFC 2401) A security gateway is an intermediate system that acts as the communications interface between two networks. The set of hosts (and networks) on the external side of the security gateway is viewed as untrusted (or less trusted), while the networks and hosts and on the internal side are viewed as trusted (or more trusted). The internal subnets and hosts served by a security gateway are presumed to be trusted by virtue of sharing a common, local, security administration. In the IPsec context, a security gateway is a point at which AH and/or ESP is implemented in order to serve a set of internal hosts, providing security services for these hosts when they communicate with external hosts also employing IPsec (either directly or via another security gateway).

SPI, Security Parameters Index.
(RFC 2401) The combination of a destination address, a security protocol, and an SPI uniquely identifies a security association. The SPI is carried in AH and ESP protocols to enable the receiving system to select the SA under which a received packet will be processed. An SPI has only local significance, as defined by the creator of the SA (usually the receiver of the packet carrying the SPI); thus an SPI is generally viewed as an opaque bit string. However, the creator of an SA may choose to interpret the bits in an SPI to facilitate local processing.

Traffic analysis.
(RFC 2401) The analysis of network traffic flow for the purpose of deducing information that is useful to an adversary. Examples of such information are frequency of transmission, the identities of the conversing parties, sizes of packets, flow identifiers, etc.

Trusted subnetwork.
(RFC 2401) A subnetwork containing hosts and routers that trust each other not to engage in active or passive attacks. There also is an assumption that the underlying communications channel (e.g., a LAN or CAN) isn't being attacked by other means.


[RFC 2316] Report of the IAB Security Architecture Workshop.

[RFC 2411] IP Security Document Roadmap.

[RFC 2709] Security Model with Tunnel-mode IPsec for NAT Domains.

[RFC 2828] Internet Security Glossary.

[RFC 3554] On the Use of Stream Control Transmission Protocol (SCTP) with IPsec.

[RFC 3566] The AES-XCBC-MAC-96 Algorithm and Its Use With IPsec.

[RFC 3585] IPsec Configuration Policy Information Model.

[RFC 3586] IP Security Policy (IPSP) Requirements.

[RFC 3602] The AES-CBC Cipher Algorithm and Its Use with IPsec.

[RFC 3715] IPsec-Network Address Translation (NAT) Compatibility Requirements.

[RFC 3723] Securing Block Storage Protocols over IP.

[RFC 3740] The Multicast Group Security Architecture.

[RFC 3776] Using IPsec to Protect Mobile IPv6 Signaling Between Mobile Nodes and Home Agents.

[RFC 3884] Use of IPsec Transport Mode for Dynamic Routing.

[RFC 4196] The SEED Cipher Algorithm and Its Use with IPsec.

[RFC 4301] Security Architecture for the Internet Protocol.

[RFC 4308] Cryptographic Suites for IPsec.

[RFC 4312] The Camellia Cipher Algorithm and Its Use With IPsec.

[RFC 4494] The AES-CMAC-96 Algorithm and Its Use with IPsec.

[RFC 5374] Multicast Extensions to the Security Architecture for the Internet Protocol.

[RFC 5386] Better-Than-Nothing Security: An Unauthenticated Mode of IPsec.

[RFC 5387] Problem and Applicability Statement for Better-Than-Nothing Security (BTNS).

[RFC 5406] Guidelines for Specifying the Use of IPsec Version 2.

[RFC 5856] Integration of Robust Header Compression over IPsec Security Associations.

[RFC 5858] IPsec Extensions to Support Robust Header Compression over IPsec.

[RFC 6027] IPsec Cluster Problem Statement.


Obsolete RFCs:

[RFC 1825] Security Architecture for the Internet Protocol.

[RFC 2401] Security Architecture for the Internet Protocol.

[RFC 2407] The Internet IP Security Domain of Interpretation for ISAKMP.

Description Glossary RFCs Publications Obsolete RFCs