I
I-SID (Service Instance Identifier)
A field in an
I-TAG that defines the service instance to which the
Provider Backbone Bridging (PBB) frame is mapped.
I-TAG
Incoming Label Map (ILM)
ingress
Inbound or incoming, referring to a
protocol data unit (PDU) entering a device. See also
egress.
Institute of Electrical and Electronics Engineers (IEEE)
A coordinating body for computing and communications standards. The IEEE mainly covers
Layer 1 (L1) and
Layer 2 (L2) of the
Open Systems Interconnection (OSI) Reference Model. (Pronounced “eye-triple-ee”.)
See
http://www.ieee.org.
interface
The point at which a connection is made between two devices. An interface describes the logical and physical connections and usually means the same thing as the term
port.
Interior Gateway Protocol (IGP)
Intermediate System to Intermediate System (IS-IS)
An
Interior Gateway Protocol (IGP) that floods
link state information throughout a network of routers. Each IS-IS router independently builds a database of the network's topology, aggregating the flooded network information. A
Routing Information Base (RIB) is calculated from the database by constructing a
shortest path tree (SPT).
Like
Open Shortest Path First (OSPF), IS-IS uses the
Dijkstra algorithm to find the best path through a network. Packets are then forwarded, based on the computed ideal path, through the network to the destination.
internal spanning tree (IST)
A special type of
multiple spanning-tree instance (MSTI) that runs in an
multiple spanning-tree (MST) region. An IST connects all the switches in the MST region and appears as a subtree in the
common and internal spanning tree (CIST) that encompasses the entire switched domain.
An IST is identified by the number zero (0) and exists on all ports; you cannot delete the IST. By default, all VLANs are assigned to the IST. The IST is the only spanning tree instance that sends and receives
bridge protocol data unit (BPDU) messages.
Any other spanning tree instance within an MST region is called a
multiple spanning-tree instance (MSTI).
International Organization for Standardization (ISO)
An international standards body that establishes global standards for communications and information exchange. Voting members are designated standards bodies of participating nations;
American National Standards Institute (ANSI) is the U.S. member of the ISO. The
Open Systems Interconnection (OSI) Reference Model is one of the ISO’s most widely accepted recommendations.
Sometimes mistakenly referred to as the “International Standards Organization”. Because “International Organization for Standardization” has different acronyms in different languages (IOS in English, OIN in French for Organisation internationale de normalisation), the founders gave it the short form ISO. ISO is derived from the Greek isos, meaning “equal”.
International Telecommunication Union (ITU)
An international organization that develops standards for telecommunications. Formerly known as the CCITT. See
http://www.itu.int.
Internet
The world’s largest computer network, serving universities, commercial interests, government agencies, and private individuals. The Internet uses
Transmission Control Protocol/Internet Protocol (TCP/IP) protocols, and Internet computers and devices run many different operating systems.
No government agency, single person, or corporate entity controls the Internet. All decisions on methods and standards are made by standards groups based on input from users.
Internet Control Message Protocol (ICMP)
An
Internet Protocol (IP) that provides management and control functions. Routers send ICMP messages to respond to undeliverable datagrams by placing an ICMP message in an IP datagram and then sending the datagram back to the original source. ICMP is also used by the
ping (packet internet groper) command and enables a host to discover addresses of operating routers on the subnet. Defined in RFC 792.
IPv6 makes greater use of ICMP (ICMPv6 defined in RFC 4443) than IPv4, including neighbor solicitation, neighbor advertisement, router solicitation, router advertisement, and redirect.
Internet Engineering Task Force (IETF)
An international community of network designers, operators, vendors, and researchers that develops
Request for Comments (RFC) documents that define protocols and specifications for the Internet. The IETF mainly covers
Layer 2 (L2) and
Layer 3 (L3) of the
Open Systems Interconnection (OSI) Reference Model. See
http://www.ietf.org.
Internet Group Management Protocol (IGMP)
An IPv4 protocol that allows hosts to add or remove themselves from a
multicast group. Defined by RFC 3376.
IGMP enables receivers to register that they want to receive a particular multicast transmission, but does not route multicast traffic from the source to receivers. That task is left to a multicast routing protocol, such as
Protocol Independent Multicast (PIM).
Internet Key Exchange (IKE or IKEv2)
An
Internet Protocol Security (IPsec) protocol used to set up a security association (SA) by negotiating keys in secret. IKE builds upon
Internet Security Association and Key Management Protocol (ISAKMP) using X.509 certificates for authentication and a
Diffie–Hellman key exchange to set up a shared session secret from which cryptographic keys are derived. In addition, a security policy for every peer which will connect must be manually maintained.
The IKE protocol runs in two phases. The first phase establishes a ISAKMP SA which is used in the second phase to negotiate and set up the IPsec SAs.
Internet Protocol (IP)
A
Layer 3 (L3) protocol that provides
connectionless delivery of data across heterogeneous physical networks. IP provides features for addressing, type-of-service, fragmentation and reassembly, and security. Defined by RFCs 791 and 1349.
Each computer (known as a
host) on the Internet has at least one
IP address that uniquely identifies it from all other computers on the Internet.
IP is
best effort and provides no guarantees of reliability, so if packets are lost in transit, accidentally duplicated, arrive in the wrong order, or arrive corrupted, no effort is made to address the problem on the IP level—that is left to protocols a layer above, such as
Transmission Control Protocol (TCP).
Internet Protocol Security (IPsec)
A protocol suite for securing IP communications by authenticating and encrypting packets during a communication session.
Authentication Header (AH) and
Encapsulating Security Payload (ESP) are the main wire-level protocols used by IPsec. Before either AH or ESP can be used, however, the two devices must share a public key through
Internet Key Exchange (IKE or IKEv2).
RFC 2401 specifies the base architecture for IPsec compliant systems. RFCs 2402, 2406, and 2407 provide more details about IPsec.
Internet Security Association and Key Management Protocol (ISAKMP)
A framework for authentication and key exchange with actual authenticated keying material provided either by manual configuration with pre-shared keys or
Internet Key Exchange (IKE or IKEv2). See also
Internet Protocol Security (IPsec).
IP address
A unique number that identifies a device on an
Internet Protocol (IP) network. IP addresses have two formats:
• An IPv4 address is 32 bits and is usually written in
dotted decimal notation as four decimal numbers separated by periods. For example, 192.168.50.4 is an IPv4 address.
• An IPv6 address is 128 bits and is written in a hexadecimal notation of eight 16-bit parts separated by colons. For example, FE80:0000:0000:0000:0202:B3FF:FE1E:8329 is an IPv6 address. In the
double colon address format, consecutive colons (“::”) represent successive 16-bit blocks that contain zeros: FE80::0202:B3FF:FE1E:8329. While a much larger address space is a feature, IPv6 also has other features such as multicast support, jumbograms (packets up to 4 GB in size), and stateless host auto-configuration.
Table 3-1 compares the IPv4 and IPv6 address formats.
Table 3-1: IPv6 and IPv4 Address Formats
Feature | IPv6 | IPv4 |
|---|
Address space | 128-bits = 3.4 x 1038 (340 unidecillion) | 32-bits = 4.3 x 109 (4.2 billion) |
Field separator | colon (:) | period (.) |
Notation | hexadecimal | decimal |
Example | db8:0:0:1 | 0.23.2.3 |
Each IP address contains a network part, an optional subnetwork part, and a host part. The network and subnetwork parts together are used for routing, while the host part is used to address an individual host within the network or subnetwork. A subnet mask is used to extract network and subnetwork parts from the IP address.
Classless Interdomain Routing (CIDR) provides a way to represent IP addresses and
subnet masks.
IP addresses are difficult to remember, so people tend to refer to computers by their
domain names instead.
IPv6 Provider Edge (6PE)
A protocol that enables IPv6 domains to communicate with each other over an
Multi-Protocol Label Switching (MPLS) IPv4 core network. V6PE routers are “dual stack” and run both IPv4 and IPv6. Multiprotocol
Border Gateway Protocol (BGP) (MP-BGP) in the IPv4 network is used to exchange IPv6 reachability information along with a label for each IPv6 prefix announced. Defined in RFC 4798.
Also called V6PE.
Last modified date: 07/13/2023