IS-IS in an Interior Gateway Protocol developed in the 1980s by Digital Equipment Corporation (DEC) and submitted to the International Organization for Standardization (IOS) as the routing protocol for Open System Interconnection (OSI). The creation creation of IS-IS was an attempt to produce a standard protocol suite that could allow internetworks to scale.
In recent years, the IS-IS routing protocol has become increasingly popular, with widespread usage among Service Providers. It is a link state protocol, which enables very fast convergence with large scalability. It is also a very flexible protocol and has been extended to incorporate leading edge features such as MPLS Traffic Engineering.
The IS-IS routing protocol is a link-state protocol, as opposed to distance-vector protocols such as Interior Gateway Routing Protocol (IGRP) and Routing Information Protocol (RIP). Link-state offers several advantages over distance-vector protocols. It is faster converging, supports much larger internetworks, and is less susceptible to routing loops.
Intermediate System-to-Intermediate System (IS-IS) Protocol is an intradomain Open System Interconnection (OSI) dynamic routing protocol specified in International Organization for Standardization (ISO) 10589. The protocol is designed to operate in OSI Connectionless Network Service (CLNS). Data is carried using the protocol specified in ISO 8473.
Information about IS-IS from Cisco Systems
|Adjacency|Local routing information that shows the reachability of a directly connect End System (ES)- Node or Intermediate System (IS) - Router. A separate adjacency is created for each neighbor on a circuit, and for each level of routing (that is Level 1 and Level 2) on a broadcast circuit. |Administrative Domain|A group of routers that share the same routing protocol within one organization. |Area|A subdomain with an Administrative Domain. Routers in an area maintain detailed routing information about the area's internal composition. The routers also maintain routing information that allows them to reach other areas. the area address is contained in the NET and NSAP address. |Circuit|The local routing information for a single subnet point of attachment (SNPA). |Code/Length/Value (CLV)|These are the variable-length fields in a PDU. The code field specifies the information in the Content field as a number. The length field states the size of the Value field. The Value field contains the information itself. |Complete sequence number packet (CSNP)|CSNPs describe every link in the link-state database. CSNPs are sent on point-to-point links. When the link comes up to synchronize the link-state databases. The designated router (DR), or designated intermediate system (DIS), on a multicast network sends out CSNPs every 10 seconds. |Connectionless Network Protocol (CLNP)|The is the ISO protocol used to carry data and error indications at the network layer. CLNP is similar to IP and has no facilities to detect errors in data transmission. It relies on the transport layer to provide guaranteed data delivery. |Connectionless Network Service (CLNS)|CLNS uses a datagram transfer service and does not require a circuit to be established before data is transmitted. Whereas CLNP defines the actual protocol, CLNS describes a service provided up to the transport layer. Being a connectionless service, CLNP provides a "best effort" delivery of data; therefore, there is no guarantee that the data will be lost, corrupted, misordered, or duplicated. If you require guaranteed delivery, the transport layer or application layer needs to provide the service that will correct the problems when they arise. |Designated intermediate system (DIS)|The router (IS) on a LAN that is designated to perform additional duties. In particular, the DIS generates link-state PDUs on behalf of the LAN by treating the LAN as a pseudonode. |Dual IS-IS|IS-IS that supports both OSI and IP routing information. Areas within the autonomous system can run either OSI or IP or both. However, the configuration chosen must be consistent within the entire area. |End System (ES)|The end node or host, which has limited routing capabilities. The ES has the OSO or IP Layer 3 protocol running and can receive and send data. |End System-to-Intermediate System (ES-IS)|The protocol by which the OSI ES and the IS communicate to dynamically learn Layer 2 adjacencies. |Hello|Hello packets are used to dicover and maintain adjacencies. |Host Address|This is the subset of the NET address, which includes both the domain, area, and system ID. |Integrated IS-IS|Another term for Dual IS-IS. Indicates IS-IS can be used to support routing for two Layer 3 protocols (IP and CLNP) in the same network simultaneously. |Intermediate system (IS)|A router. The IS is a device capable of directing traffic to remote destinations. |Intermediate System-to-Intermediate System (IS-IS)|The OSI routing protocol that learns the location of the network within the autonomous system so that data can be forwarded to the remote hosts.
No page links to ISIS.
