Internet Protocol Security (IPSec) is a protocol suite for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a data stream. IPSec also includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptographic keys to be used during the session. IPSec can be used to protect data flows between a pair of hosts (e.g. computer users or servers), between a pair of security gateways (e.g. routers or firewalls), or between a security gateway and a host.
IPSec is a dual mode, end-to-end, security scheme operating at the Internet Layer of the Internet Protocol Suite or OSI model Layer 3. Some other Internet security systems in widespread use, such as Secure Sockets Layer (SSL), Transport Layer Security (TLS) and Secure Shell (SSH), operate in the upper layers of these models. Hence, IPSec can be used for protecting any application traffic across the Internet. Applications need not be specifically designed to use IPSec. The use of TLS/SSL, on the other hand, must typically be incorporated into the design of applications.
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IPSec is a successor of the ISO standard Network Layer Security Protocol (NLSP). NLSP was based on the SP3 protocol that was published by NIST, but designed by the Secure Data Network System project of the National Security Agency (NSA).
IPSec is officially specified by the Internet Engineering Task Force (IETF) in a series of Request for Comments addressing various components and extensions, including the official capitalization style of the term.
The IPSec suite is a framework of open standards. IPsec uses the following protocols to perform various functions:
Internet key exchange (IKE and IKEv2) to set up a security association (SA) by handling negotiation of protocols and algorithms and to generate the encryption and authentication keys to be used by IPSec.
Authentication Header (AH) to provide connectionless integrity and data origin authentication for IP datagrams and to provide protection against replay attacks.
Encapsulating Security Payload (ESP) to provide confidentiality, data origin authentication, connectionless integrity, an anti-replay service (a form of partial sequence integrity), and limited traffic flow confidentiality.
Authentication Header (AH) is a member of the IPsec protocol suite. AH guarantees connectionless integrity and data origin authentication of IP packets. Further, it can optionally protect against replay attacks by using the sliding window technique and discarding old packets. AH protects the IP payload and all header fields of an IP datagram except for mutable fields (i.e. those that might be altered in transit)
In IPv4, mutable (and therefore unauthenticated) IP header fields include DSCP/TOS, Flags, Fragment Offset, TTL and Header Checksum.
AH operates directly on top of IP, using IP protocol number 51.
The following AH packet diagram shows how an AH packet is constructed and interpreted:
0 - 7 bit
8 - 15 bit
16 - 23 bit
24 - 31 bit
Security parameters index (SPI)
Authentication data (variable)
The Next Header is an 8-bit field that identifies the type of the next payload after the Authentication Header. The value of this field is chosen from the set of IP Protocol Numbers defined in the most recent "Assigned Numbers" RFC from the Internet Assigned Numbers Authority. See List of IP protocol numbers.
Size of AH packet.
Reserved for future use (all zero until then).
SECURITY PARAMETERS INDEX (SPI)Â
Identifies the security parameters, which, in combination with the IP address, then identify the security association implemented with this packet.
A monotonically increasing number, used to prevent replay attacks.
Contains the integrity check value (ICV) necessary to authenticate the packet; it may contain padding.
Encapsulating Security Payload
Encapsulating Security Payload (ESP) is a member of the IPsec protocol suite. In IPsec it provides origin authenticity, integrity, and confidentiality protection of packets. ESP also supports encryption-only and authentication-only configurations, but using encryption without authentication is strongly discouraged because it is insecure.Unlike Authentication Header (AH), ESP does not protect the IP packet header. However, in Tunnel Mode, where the entire original IP packet is encapsulated with a new packet header added, ESP protection is afforded to the whole inner IP packet (including the inner header) while the outer header remains unprotected. ESP operates directly on top of IP, using IP protocol number 50.
Always on Time
Marked to Standard
The following ESP packet diagram shows how an ESP packet is constructed and interpreted:[
0 - 7 bit
8 - 15 bit
16 - 23 bit
24 - 31 bit
Security parameters index (SPI)
Payload data (variable)
Padding (0-255 bytes)
Authentication Data (variable)
Security parameters index (SPI)Â
Identifies the security parameters in combination with IP address.
A monotonically increasing number, used to prevent replay attacks.
The data to be transferred.
Used with some block ciphers to pad the data to the full length of a block.
Size of padding in bytes.
Identifies the protocol of the payload data. The value of this field is chosen from the set of IP Protocol Numbers defined in the most recent "Assigned Numbers" RFC from the Internet Assigned Numbers Authority. See List of IP protocol numbers.
Contains the data used to authenticate the packet.
The IP security architecture uses the concept of a security association as the basis for building security functions into IP. A security association is simply the bundle of algorithms and parameters (such as keys) that is being used to encrypt and authenticate a particular flow in one direction. Therefore, in normal bi-directional traffic, the flows are secured by a pair of security associations. The actual choice of encryption and authentication algorithms (from a defined list) is left to the IPSec administrator.
In order to decide what protection is to be provided for an outgoing packet, IPSec uses the Security Parameter Index (SPI), an index to the security association database (SADB), along with the destination address in a packet header, which together uniquely identify a security association for that packet. A similar procedure is performed for an incoming packet, where IPSec gathers decryption and verification keys from the security association database.
For multicast, a security association is provided for the group, and is duplicated across all authorized receivers of the group. There may be more than one security association for a group, using different SPIs, thereby allowing multiple levels and sets of security within a group. Indeed, each sender can have multiple security associations, allowing authentication, since a receiver can only know that someone knowing the keys sent the data. Note that the relevant standard does not describe how the association is chosen and duplicated across the group; it is assumed that a responsible party will have made the choice.
Modes of operation
IPSec can be implemented in a host-to-host transport mode, as well as in a network tunnel mode.
In transport mode, only the payload (the data you transfer) of the IP packet is encrypted and/or authenticated. The routing is intact, since the IP header is neither modified nor encrypted; however, when the authentication header is used, the IP addresses cannot be translated, as this will invalidate the hash value. The transport and application layers are always secured by hash, so they cannot be modified in any way (for example by translating the port numbers). Transport mode is used for host-to-host communications.
A means to encapsulate IPsec messages for NAT traversal has been defined by RFC documents describing the NAT-T mechanism.
In tunnel mode, the entire IP packet (data and IP header) is encrypted and/or authenticated. It is then encapsulated into a new IP packet with a new IP header. Tunnel mode is used to create Virtual Private Networks for network-to-network communications (e.g. between routers to link sites), host-to-network communications (e.g. remote user access), and host-to-host communications (e.g. private chat).
Cryptographic algorithms defined for use with IPsec include:
HMAC-SHA1 for integrity protection and authenticity.
TripleDES-CBC for confidentiality
AES-CBC for confidentiality.
IPSec support is usually implemented in the kernel with key management and ISAKMP/IKE negotiation carried out from user-space. Existing IPSec implementations often include both. However, as there is a standard interface for key management, it is possible to control one kernel IPSec stack using key management tools from a different implementation.
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Because of this, there is sometimes confusion as to the origins of the IPsec implementation in the Linux kernel. The FreeS/WAN project made the first complete and open source implementation of IPsec for Linux. It consists of a kernel IPsec stack (KLIPS), as well as a key management daemon (pluto) and many shell scripts. The FreeS/WAN project was disbanded in March 2004. Openswan and strongSwan are continuations of FreeS/WAN. The KAME project also implemented complete IPsec support for NetBSD, FreeBSD. Its key management daemon is called racoon. OpenBSD made its own ISAKMP/IKE daemon, simply named isakmpd (which was also ported to other systems, including Linux).
None of those kernel IPsec stacks were integrated into the Linux kernel. Alexey Kuznetsov and David S. Miller wrote a kernel IPsec implementation from scratch for the Linux kernel around the end of 2002. This stack was subsequently released as part of Linux 2.6, and is referred to variously as "native" or "NETKEY".
Thus, the current Linux IPsec stack did not originate from the KAME project. Since it supports the standard PF KEY protocol (RFC 2367) and the native XFRM interface for key management, the Linux IPsec stack can be used in conjunction with either pluto from Openswan/strongSwan, isakmpd from the OpenBSD project, racoon from the KAME project, or without any ISAKMP/IKE daemon (using manual keying).
The new architectures of network processors, including multi-core processors with integrated encryption engines, suggested some changes in the way the IPsec stacks are designed. A dedicated Fast Path is currently being commonly used to offload IPsec processing (SA, SP lookups, encryption, etc.). These Fast-Path IPsec-stack instances, running on dedicated cores, must be integrated with Linux or RTOS instances, running on other cores, which control them.
There exist a number of implementations of IPsec and ISAKMP/IKE protocols. These include:
NRL IPsec, one of the original sources of IPsec code.
OpenBSD, with its own code derived from a BSD/OS implementation written by John Ioannidis and Angelos D. Keromytis in 1996.
The KAME stack, that is included in Mac OS X, NetBSD and FreeBSD.
"IPsec" in Cisco IOS Software .
"IPsec" in Microsoft Windows, including Windows XP, Windows 2000, Windows 2003, Windows Vista, Windows Server 2008, and Windows 7.
IPsec in Windows Vista and later
SafeNet QuickSec toolkits.
IPsec in Solaris
IBM AIX operating system
IPsec and IKE in HP-UX (HP-UX IPSec)
 Standards status
IPsec was developed in conjunction with IPv6 and is therefore mandatory in all standards-compliant implementations of IPv6, but its implementation is an optional extension to IPv4. However, because of the slow deployment of IPv6, IPsec is most commonly used to secure IPv4 traffic. IPsec protocols were originally defined in Requests for Comments RFC 1825 and RFC 1829, published in 1995. In 1998, these documents were superseded by RFC 2401 and RFC 2412 with incompatible aspects, although they were conceptually identical. In addition, a mutual authentication and key exchange protocol Internet Key Exchange (IKE) was defined to create and manage security associations. In December 2005, new standards were defined in RFC 4301 and RFC 4309 which are largely a superset of the previous editions with a second version of the Internet Key Exchange standard IKEv2. These third-generation documents standardized the abbreviation of IPsec to uppercase "IP" and lowercase "sec". It is unusual to see any product that offers support for RFCs 1825 and 1829. "ESP" generally refers to RFC 2406, while ESPbis refers to RFC 4303.
Since mid-2008, an IPsec Maintenance and Extensions working group is active at the IETF.
In a network designed to deliver a multicast service (like video) using IGMP, what type of basic architecture would be used? Explain with the aid of a diagram. (5)
Internet Group Management Protocol (IGMP)
Internet Group Management Protocol (IGMP) is the protocol used to support multicasting. To use multicasting, a process on a host must be able to join and leave a group.
A process is a user program that is using the network. Group access is identified by the group address and the interface (NIC).
A host must keep track of the groups that at least one process belongs to and the number of processes that belong to the group. IGMP is defined in RFC 1112.
IGMP messages are used by multicast routers to track group memberships on each of its networks.
It uses these rules:
1. The first time a process on a host joins a multicast group, the host will send an IGMP report. This means that every time the host needs to receive messages from a new group to support its processes, it will send a report.
2. Multicast routers will send IGMP queries regularly to determine whether any hosts are running processes that belong to any groups. The group address of the query is set to 0, the TTL field is set to 1, and the destination IP address is 184.108.40.206 which is the all hosts group address which addresses all the multicast capable routers and hosts on a network.
3. A host sends one IGMP response for each group that contains one or more processes. The router expects one response from each host for each group that one or more of its processes require access to.
4. A host does not send a report when its last process leaves a group (when the group access is no longer required by a process). The multicast router relies on query responses to update this information.
IGMP is defined in RFC 1112. Hosts and routers use IGMP to support multicasting. Multicast routers
must know which hosts belong to what group at any given point of time. The IGMP message is 8 bytes.
1. Bits 0 to 3 - IGMP version number
2. Bits 4 to 7 - IGMP type. 1=query sent by a multicast router. 2 is a response sent by a host.
3. Bits 8 to 15 - unused
4. Bits 16 to 31 - Checksum
5. The last 4 bytes - 32 bit group address which is the same as the class D IP address.
IGMP message formats are encapsulated in an IP datagram which contain a time to live (TTL) field.
The default is to set the TTL field to 1 which means the datagram will not leave its sub network.
An application can increase its TTL field in a message to locate a server distance in terms of hops.
Addresses from 220.127.116.11 to 18.104.22.168 are not forwarded by multicast routers since these addresses are intended for applications that do not need to communicate with other networks. Therefore these
Internet Group Management Protocol addresses can be used for group multicasting on private networks with no concern for addresses being
used for multicasting on other networks.