The Enduring Relevance of IS-IS in Interior Routing Protocols

While the Domain Name System (DNS) and Border Gateway Protocol (BGP) have garnered much attention in the networking community over the years, there is another interior routing protocol that has quietly held significant sway over a large portion of the backbone internet infrastructure: the Intermediate System to Intermediate System (IS-IS) routing protocol. This protocol, while often overlooked, has seen a resurgence in visibility and usage.

Current State of IS-IS

Contrary to popular belief, IS-IS is not a dormant or deprecated protocol. In fact, there is more adoption and usage of IS-IS today than there has been in many years. It is not only utilized explicitly in certain Service Provider (SP) environments, but is increasingly becoming an integral part of vendor offerings. Companies such as Cisco have utilized IS-IS in their MAC-in-MAC encapsulation and transport solutions, such as FabricPath, and their more recent Advanced Confidentiality and Innovation Infrastructure (ACI) products.

Other vendors have embraced IS-IS as well, showing its widespread utility and adaptability. Despite the growing adoption of Internet Protocol (IP) routing protocols, IS-IS has remained robust and purposeful, serving as a reliable backbone for various network operations.

Extensibility and Flexibility

One of the key features that sets IS-IS apart is its exceptional ability to carry a wide variety of information types. This protocol was designed with extensibility in mind, allowing it to easily incorporate new data and information as the network landscape evolves. This contrasts with protocols like OSPF, which have required significant re-engineering to adapt to new trends and requirements.

For instance, IS-IS was one of the first, and arguably the best, at carrying topology information for Multiprotocol Label Switching (MPLS) traffic engineering. It can also seamlessly handle the transition to IPv6, making it a preferred protocol in many large-scale networks. The ease with which IS-IS can be adapted to new technologies positions it as a strong candidate for future requirements in network infrastructure.

Security and Reliability

One of the most compelling advantages of IS-IS lies in its inherent security and reliability. Unlike IP-based routing protocols, IS-IS is less susceptible to certain types of attacks, primarily due to its non-IP nature. This characteristic has made it a popular choice among service providers looking to secure their networks.

As network environments have become more complex, the robustness of IS-IS has not gone unnoticed. Despite the fact that many ISPs may still operate OSPF, a handful of Tier 1 service providers have leveraged IS-IS to manage a large volume of traffic, highlighting its reliability and efficiency.

Future Prospects

While IS-IS may not be growing in terms of absolute percentage of the network, there is still significant merit in maintaining or transitioning to this protocol. The ease with which it can adapt to new requirements and its ability to enhance network security and resilience make it an attractive solution for modern network infrastructure.

As the network environment continues to evolve, IS-IS remains a reliable and future-proof choice. Its extensibility, security, and proven track record in managing large-scale networks make it an ideal candidate for ensuring the continuity and reliability of enterprise and service provider networks.