Last updated on Jun 26, 2024
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IS-IS vs OSPF: The Basics
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IS-IS vs OSPF: The Advantages
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IS-IS vs OSPF: The Challenges
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IS-IS vs OSPF: The Trade-offs
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IS-IS vs OSPF: The Best Practices
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Here’s what else to consider
If you are a network engineer, you probably know that there are many routing protocols to choose from when designing your network. Two of the most popular ones are OSPF and IS-IS, both of which are link-state protocols that use the Dijkstra algorithm to calculate the shortest paths. However, they have some significant differences that can affect your network performance, scalability, and security. In this article, we will explore why you should consider choosing IS-IS over OSPF for your network, and what are the benefits and challenges of doing so.
Key takeaways from this article
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Simplified network management:
IS-IS protocol's single LSP and routing domain streamline operations, reducing complexity for easier network management and maintenance.
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Smooth IPv6 transition:
Migrating to IPv6 is a breeze with IS-IS, as it only requires enabling IPv6 in the existing process, unlike OSPF's need for a separate OSPFv3 configuration.
This summary is powered by AI and these experts
- Hessam Khorsand Network Infrastructure
- Martin Indeche Network Transmission Engineer at…
1 IS-IS vs OSPF: The Basics
IS-IS stands for Intermediate System to Intermediate System, and it is a routing protocol that was originally developed for the OSI (Open Systems Interconnection) model. OSPF stands for Open Shortest Path First, and it is a routing protocol that was designed for the TCP/IP (Transmission Control Protocol/Internet Protocol) model. Both protocols operate at the network layer and use link-state advertisem*nts (LSAs) to exchange information about the topology and the status of the links. However, IS-IS uses a single type of LSA, called a link-state PDU (LSP), while OSPF uses five types of LSAs, each with a different function and scope.
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- Hessam Khorsand Network Infrastructure
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Both protocols are link-state and widely used in networking, OSPF devide networks into area's and ISIS devide networks into levels, ISIS generally converges faster than OSPF in large networks due to its more efficient flooding mechanism and OSPF in more commonly implemented and supported by a wider range of vendors.
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IS-IS and OPSF both are link-state protocol and Dijkstra algorithm to find the shortest path. However, there is difference in the type of LSA as IS-IS use single type but OSPF use multiple type of LSA to distribute routing information such as a Router LSA, Network LSA, ASBR Summary LSA etc.
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One Liner-Network Design Flexibility &IS-IS is Less Dependent on IP Addressing, IS-IS is a Layer 2 protocol and does not rely on IP addresses for its core routing operations. This independence from IP addressing schemes can offer more flexibility in network design and renumbering.
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2 IS-IS vs OSPF: The Advantages
One of the main advantages of IS-IS over OSPF is that it is simpler and more efficient. IS-IS uses a single LSP type, which reduces the complexity and overhead of processing and storing multiple types of LSAs. IS-IS also uses a single routing domain, which eliminates the need for area border routers (ABRs) and autonomous system boundary routers (ASBRs) that are required in OSPF to connect different areas and external routes. IS-IS also supports multiple address families, such as IPv4 and IPv6, in a single instance, which makes it easier to migrate and integrate different networks. Moreover, IS-IS has a faster convergence time than OSPF, as it uses a partial SPF (shortest path first) calculation instead of a full SPF calculation when a change occurs in the network.
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- Hessam Khorsand Network Infrastructure
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ISIS is increasingly favored over OSPF in Service Provider core networks due to its superior ease of configuration, flexibility, and scalability. Unlike OSPF, which operates at the IP layer, ISIS functions over Layer 2. OSPF requires IP connectivity between routers for routing information exchange, while ISIS sends updates via CLNS, eliminating the need for IP connectivity. Additionally, OSPF is more susceptible to attacks, necessitating security measures, whereas ISIS, operating at Layer 2, faces fewer security risks. When transitioning from IPv4 to IPv6, migrating from OSPFv2 to OSPFv3 involves configuration changes, whereas ISIS simply requires the addition of an IPv6 address family.
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Here are some reasons why you would want to pick IS-IS over OSPF for your network. IS-IS is frequently used in large-scale and service provider networks because of it ability to scale and be stable. It works directly on Layer 2 and requires no IP for routing information which can improve performance and troubleshooting. Since IS-IS provides a larger address space as it was prepped for IPv6, again such that you could scale to any network size, which will improve system topology hierarchically, complex network routing mechanisms will be easily and efficiently implemented since the design was planned to be hierarchical in the beginning. Furthermore, IS-IS is very versatile when it comes to such a wide array of network topologies.
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3 IS-IS vs OSPF: The Challenges
One of the main challenges of IS-IS over OSPF is that it is less familiar and less widely supported. IS-IS was originally designed for the OSI model, which is not as common as the TCP/IP model in today's networks. Therefore, some network engineers may not have the same level of expertise and experience with IS-IS as they do with OSPF. IS-IS also may not be compatible with some legacy devices or applications that only support OSPF or other TCP/IP-based protocols. Furthermore, IS-IS may have some limitations in terms of security and flexibility. IS-IS does not support authentication or encryption of LSPs, which may expose the network to unauthorized access or modification. IS-IS also does not support route summarization or filtering, which may affect the network scalability and control.
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4 IS-IS vs OSPF: The Trade-offs
When deciding between IS-IS and OSPF for your network, there is no one-size-fits-all answer. It depends on your network size, topology, requirements, and preferences. However, some general trade-offs to consider are that IS-IS is simpler and more efficient, as it uses a single LSP type, a single routing domain, and a single instance for multiple address families; whereas OSPF is more widely used and supported in the TCP/IP model by various devices and applications. Additionally, IS-IS does not support authentication or encryption of LSPs, while OSPF does not support partial SPF calculation or multiple address families in a single instance. Ultimately, you must weigh the benefits and drawbacks of both protocols to determine which one is best for your network.
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5 IS-IS vs OSPF: The Best Practices
No matter which protocol you decide to use, it is essential to follow best practices for optimal network performance, scalability, and security. This includes planning your network design carefully and documenting your topology, configuration, and policies. Additionally, you should monitor your network performance and troubleshoot any issues or anomalies that may arise. It is also important to update your network devices and software regularly, apply the latest patches, and use appropriate tools and techniques for routing optimization. Prior to implementing any changes in production, it is important to test them out and have a backup and recovery plan ready in case of disasters.
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6 Here’s what else to consider
This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?
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- Martin Indeche Network Transmission Engineer at Innovis | IP | EBK | Msc Computer Science I Mentor
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If you are migrating your network to IPV6, it's very easy when running IS-IS Protocol than OSPF. With ISIS you just need to enable IPv6 functionality in the existing ISIS process and that is it. With OSPF you need to configure OSPFv3 for you to support IPv6. So migration to IPv6 with ISIS is more easy and smooth
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