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Authentication Header - seeks to provide security by adding authentication information to an IP datagram. This authentication information is calculated using all of the fields in the IP datagram (including not only the IP Header but also other headers and the user data) which do not change in transit.

8 16 32
Next header Length Reserved
Security parameters index
Authentication data
(variable number of 32-bit words)
Structure of the AH header in 32 bit lines.


Encapsulating Security Payload - seeks to provide confidentiality and integrity by encrypting data to be protected and placing the encrypted data in the data portion of the IP ESP. Depending on the user's security requirements, this mechanism may be used to encrypt either a transport-layer segment (e.g., TCP, UDP, ICMP, IGMP) or an entire IP datagram. Encapsulating the protected data is necessary to provide confidentiality for the entire original datagram.

Security association identifier (SPI)
Opaque transform data (variable length)
Structure of the ESP header in 32 bit lines.


Transport Layer Security - is to provide privacy and data integrity between two communicating applications. The protocol is composed of two layers: the TLS Record Protocol and the TLS Handshake Protocol. At the lowest level, layered on top of some reliable transport protocol (e.g., TCP[TCP]), is the TLS Record Protocol.


Border Gateway Protocol version 4 - is an inter-Autonomous System routing protocol. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. BGP-4 provides a new set of mechanisms for supporting classes interdomain routing.

16B 2B 1B
Marker Length Type
Structure of the BGP-4 header.


Exterior Gateway Protocol - exists in order to convey net-reachability information between neighboring gateways, possibly in different autonomous systems. The protocol includes mechanisms to acquire neighbors, monitor neighbor reachability and exchange net-reachability information in the form of Update messages. The protocol is based on periodic polling using Hello/I-Heard-You (I-H-U) message exchanges to monitor neighbor reachability and Poll commands to solicit Update responses.

8 16 24 32
EGP Version Type Code Status
Checksum Autonomous System number
Sequence number
Structure of the EGP header in 32 bit lines.


Enhanced Interior Gateway Routing Protocol - is an enhanced version of IGRP. IGRP is Cisco's Interior Gateway Routing Protocol used in TCP / IP and OSI internets. It is regarded as an interior gateway protocol (IGP) but has also been used extensively as an exterior gateway protocol for inter-domain routing. IGRP uses distance vector routing technology. The same distance vector technology found in IGRP is also used in EIGRP, and the underlying distance information remains unchanged. The convergence properties and the operating efficiency of this protocol have improved significantly.

8 16 32
Version Opcode Checksum
Sequence number
Acknowledge number
Autonomous system number
Type Length
Structure of the EIGP header in 32 bit lines.


Generic Routing Encapsulation - provides a mechanism for encapsulating arbitrary packets within an arbitrary transport protocol. In the most general case, a system has a packet that needs to be encapsulated and routed (the payload packet). The payload is first encapsulated in a GRE packet, which possibly also includes a route. The resulting GRE packet is then encapsulated in some other protocol and forwarded (the delivery protocol).

16 32
Flags Protocol type
Checksum (optional) Offset (optional)
Key (optional)
Sequence number (optional)
Routing (optional)
Structure of the GRE header in 32 bit lines.

The format of the enhanced GRE header is as follows:

16 32
Flags Protocol type
Key (HW) payload length
Key (LW) call ID
Sequence number (optional)
Acknowledgement number (optional)
Structure of the Enhanced GRE header in 32 bit lines.


Hot Standby Router Protocol - provides a mechanism which is designed to support non-disruptive failover of IP traffic in certain circumstances. In particular, the protocol protects against the failure of the first hop router when the source host cannot learn the IP address of the first hop router dynamically. The protocol is designed for use over multi-access, multicast or broadcast capable LANs (e.g., Ethernet). A large class of legacy host implementations that do not support dynamic discovery are capable of configuring a default router. HSRP provides failover services to those hosts.

8 16 24 32
Version Op code State Hellotime
Holdtime Priority Group Reserved
Authentication data
Authentication data
Virtual IP address
Structure of the HSRP header in 32 bit lines.


Interior Gateway Routing Protocol - was developed by the Cisco company. It is used to transfer routing information between routers. IGRP is sent using IP datagrams with IP 9 (IGP). The packet begins with a header which starts immediately after the IP header.

Structure of the IGRP header in 8 bit lines.



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  Citing of this page:
Radic, Drago. " IT - Informatics Alphabet " Split-Croatia.
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