IS-IS

IS-IS
Name	IS-IS
Developer	International Organization for Standardization
Introduction	1990s
Type	Interior gateway protocol
Status	Active

IS-IS

IS-IS is an interior gateway routing protocol originally standardized by the International Organization for Standardization and later adapted for routing in OSI and Internet Protocol networks. It operates as a link-state protocol for exchanging topology information among routers within an administrative domain such as an Autonomous system and is widely used by service providers, enterprises, and academic networks including deployments by AT&T, Verizon, Cisco Systems, Juniper Networks, and research backbones like Internet2. The protocol's design and extensions intersect with standards bodies and specifications from organizations such as the Internet Engineering Task Force, European Telecommunications Standards Institute, and vendor drafts influencing operators like Level 3 Communications and NTT Communications.

Overview

IS-IS is a link-state interior gateway protocol that builds a distributed topology database using Link State PDUs exchanged among routers; it is conceptually aligned with other link-state protocols used by network operators including Open Shortest Path First and has been compared in operational practice to variants in large networks run by Google, Amazon, Facebook, and Microsoft. Its operation is applicable to IPv4 and IPv6 routing and it supports multi-area designs used by transit providers such as CenturyLink and content delivery networks like Akamai Technologies. The protocol's modularity enables deployment with technologies such as MPLS, Segment Routing, and integration with control planes deployed by carriers like Telefonica and Deutsche Telekom.

History and Development

IS-IS arose from early protocol work in the International Organization for Standardization for the Open Systems Interconnection stack and was formalized in standards influenced by research at institutions such as Xerox PARC and companies including Digital Equipment Corporation and Sun Microsystems. The protocol was adapted for IP routing in proposals debated at the Internet Engineering Task Force and incorporated into operational practice by regional networks like JANET and national research networks such as SURFnet. Subsequent extensions and interoperability efforts involved contributions from Cisco Systems, Juniper Networks, Nokia, Ericsson, and standards updates through IETF working groups and authors including contributors from Bell Labs and academic groups at MIT and Stanford University.

Protocol Architecture and Operation

IS-IS uses a two-level hierarchical area structure—Level 1 and Level 2—to provide intra-area and inter-area routing, analogous in role to area constructs used in deployments by Sprint and regional carriers like T-Mobile. Routers exchange Link State PDUs with neighbor discovery using mechanisms similar to adjacency procedures in protocols adopted by Cisco Systems and Juniper Networks. The protocol supports adjacency formation on technologies such as Ethernet, SONET, Frame Relay, and point-to-point links used in optical networks operated by NTT Communications and Orange S.A.. Traffic engineering and label distribution are often combined with IS-IS in environments using Multi-Protocol Label Switching and Constraint-Based Routing as found in carrier networks by BT Group and Telefonica.

Addressing and Packet Formats

IS-IS originally used Network Service Access Point addressing in the OSI model and was extended to carry Internet Protocol version 4 and Internet Protocol version 6 reachability information via TLV encodings defined in standards referenced by the Internet Engineering Task Force. Packet types include Hello PDUs, Link State PDUs, Sequence Number PDUs, and CSNP/PSNP messages used to synchronize databases in deployments by operators like Clearwire and Time Warner Cable. Addressing and TLV extensibility have enabled support for features such as IPv4/IPv6 unicast, route targets for VPN services used by carriers like AT&T and Verizon Business, and extensions for Traffic Engineering attributes promoted by Juniper Networks and Cisco Systems.

Routing Algorithms and Metrics

The protocol uses a Dijkstra shortest-path-first computation similar to algorithms used in academic work at Carnegie Mellon University and University of California, Berkeley; metric calculation, path selection, and additive metrics may be adapted for administrative policies used by networks such as Orange S.A. or Telefonica. IS-IS supports wide metrics, administrative weights, and extensions for constraint-based routing and segment routing, enabling implementations used by Akamai Technologies and large cloud networks like Google Cloud Platform to optimize traffic engineering. Convergence behavior and scalability have been analyzed in studies associated with Internet2, RENATER, and corporate research labs at IBM Research and Microsoft Research.

Deployment and Configuration

IS-IS is commonly deployed in service provider cores, content networks, and large enterprise WANs operated by companies such as AT&T, Verizon, CenturyLink, NTT Communications, Comcast, and cloud providers like Amazon Web Services. Configuration typically involves area design, level assignment, metric tuning, and authentication, with vendor-specific CLI and management tools from Cisco Systems, Juniper Networks, Arista Networks, and Huawei Technologies. Integration with orchestration and monitoring systems from SolarWinds, Nagios, Zabbix, and SDN controllers developed by OpenDaylight and ONOS facilitates operational tasks in networks run by Deutsche Telekom and research networks like GÉANT.

Security and Robustness

Security considerations include authentication of PDUs, protection against spoofing, and mitigation of flooding and resource exhaustion—topics addressed in operational guidance from Internet Engineering Task Force documents and vendor advisories by Cisco Systems and Juniper Networks. Robustness practices used by carriers including Level 3 Communications and Telefonica involve route dampening, control-plane policing, and secure management plane integration with systems from RSA Security and Thales Group. Research into protocol hardening has involved academic projects at MIT, ETH Zurich, TU Delft, and contributions from security groups at Google and Microsoft.

Category:Routing protocols