What is Route Redistribution?

Updated on July 22, 2025

Network engineers face a complex challenge when managing enterprise networks that span multiple routing protocols. Route redistribution provides a solution, but it comes with significant risks that demand careful consideration. Understanding this process is essential for anyone designing or maintaining multi-protocol network environments.

Route redistribution serves as a bridge between different routing domains, enabling communication across networks that would otherwise remain isolated. This capability becomes critical during network migrations, mergers, or when different departments manage their networks independently. However, the process introduces complexities that can destabilize network operations if not properly managed.

This technical guide explores the mechanisms, applications, and challenges of route redistribution. We’ll examine how it works, when to use it, and why it requires exceptional care to implement successfully.

Definition and Core Concepts

Route redistribution is a networking process where routing information learned from one routing protocol is injected into another, different routing protocol. This allows routes to be shared between otherwise isolated routing domains, enabling communication between networks managed by different routing protocols.

Routing Domain

A routing domain consists of a set of routers running the same routing protocol. These routers share routing information using a common language and metric system. Examples include an Open Shortest Path First (OSPF) area or an Enhanced Interior Gateway Routing Protocol (EIGRP) autonomous system.

Different Routing Protocols

Modern networks often employ multiple routing protocols, each with distinct characteristics. OSPF uses link-state algorithms and cost-based metrics. EIGRP employs advanced distance-vector algorithms with composite metrics based on bandwidth and delay. Routing Information Protocol (RIP) uses simple hop-count metrics. Border Gateway Protocol (BGP) serves as an exterior gateway protocol for inter-domain routing.

Route Injection and Advertisement

Route injection involves taking routes from one source protocol and making them available to another protocol. The redistribution point advertises these routes to neighboring routers in the destination protocol’s domain. This process requires careful metric translation to ensure proper route selection.

Redistribution Point (Boundary Router)

The boundary router serves as the redistribution point where multiple routing protocols converge. This router maintains separate routing tables for each protocol and performs the critical function of translating routes between protocols. It must run multiple routing protocols simultaneously to facilitate the redistribution process.

Administrative Distance (AD)

Administrative Distance represents a router’s preference for routing sources when multiple protocols provide routes to the same destination. Lower AD values indicate higher preference. This value becomes crucial during redistribution to prevent routing loops and ensure optimal path selection. For example, EIGRP has an AD of 90, while OSPF has an AD of 110.

Route Metric

Route metrics determine the “cost” of a path within a specific routing protocol. Different protocols use incompatible metric systems. RIP uses hop count, EIGRP uses a composite metric based on bandwidth and delay, and OSPF uses cost calculations based on link bandwidth. This metric incompatibility creates significant challenges during redistribution.

How It Works

Route redistribution follows a systematic process that requires careful configuration and monitoring. Understanding each step helps network engineers implement redistribution successfully while avoiding common pitfalls.

Route Learning

The redistribution router learns routes from its configured routing protocols. Each protocol populates its own protocol-specific database (e.g., an OSPF Link-State Database or an EIGRP Topology Table) and then contributes its best routes to the router’s central Routing Information Base (RIB). The router stores these routes separately, maintaining protocol boundaries until redistribution occurs.

Injection into Another Protocol

Network administrators configure the router to redistribute routes from one source protocol into another. This configuration specifies which routes to redistribute and any filtering criteria. For example, routes learned via OSPF can be advertised into EIGRP, allowing EIGRP routers to reach OSPF destinations.

Metric Translation

Metric translation represents the most critical and challenging aspect of redistribution. When routes are redistributed, their original metric from the source protocol cannot be directly compared or mathematically converted into a metric compatible with the destination routing protocol due to incompatible metric systems. Instead, the boundary router assigns a new metric to the redistributed route, often using a configurable default value or an administrator-defined metric, within the destination protocol’s metric system.

Default metrics vary by protocol. OSPF typically assigns a default metric of 20 to redistributed routes. EIGRP may use a default metric based on bandwidth and delay values. This translation can cause redistributed routes to appear more or less attractive than they actually are, leading to suboptimal routing decisions.

Advertisement to New Domain

The boundary router advertises redistributed routes to its neighbors within the destination routing protocol’s domain. These neighbors treat the redistributed routes as external routes, often marking them with specific attributes to indicate their origin. The routes then propagate throughout the destination domain according to that protocol’s rules.

Loop Prevention Challenges

Route redistribution creates several loop prevention challenges that require careful management:

• Bi-directional Redistribution: Redistributing routes in both directions between two protocols can easily create routing loops. A route learned from Protocol A and redistributed into Protocol B might be redistributed back into Protocol A, creating a feedback loop.
• Suboptimal Routing: Metric translation can make redistributed routes appear better than native routes, causing traffic to take inefficient paths. A route with a high cost in its native protocol might receive a low default metric after redistribution.
• Router’s AD Preference: Routers prefer routes from protocols with lower Administrative Distance values. This preference can influence redistribution behavior and create unexpected routing patterns when multiple protocols provide routes to the same destination.

Key Features and Components

Route redistribution incorporates several key features that network engineers must understand to implement it effectively.

Inter-Protocol Routing

Redistribution enables communication between networks running different routing protocols. This capability allows organizations to maintain diverse routing environments while ensuring end-to-end connectivity. It supports gradual protocol migrations and integration of acquired networks.

Complex Control Requirements

Successful redistribution requires careful design and configuration. Network engineers must understand the behavior of all involved protocols, their metric systems, and potential interaction effects. This complexity demands thorough planning and extensive testing before implementation.

Metric Translation Mechanisms

The metric translation process adapts route “cost” information for the destination protocol. Since protocols use incompatible metric systems, this translation often involves default values or administratively configured metrics. The translation process significantly impacts route selection and traffic flow patterns.

Loop and Suboptimal Path Risks

Redistribution introduces primary challenges including routing loops and suboptimal paths. These issues require proactive management through filtering, tagging, and careful metric configuration. Understanding these risks helps engineers implement appropriate safeguards.

Filtering and Tagging Tools

Advanced redistribution implementations use filtering and tagging to control which routes are redistributed and how they behave. Route maps, prefix lists, and distribute lists provide granular control over the redistribution process. Route tagging allows policies to track and manage redistributed routes throughout the network.

Use Cases and Applications

Route redistribution serves specific purposes in enterprise networking environments. Understanding these use cases helps determine when redistribution is appropriate and how to implement it effectively.

Network Mergers and Acquisitions

Organizations acquiring companies often need to integrate networks using different routing protocols. Redistribution enables immediate connectivity while planning long-term protocol standardization. This approach allows business operations to continue while technical teams develop integration strategies.

Protocol Migration Projects

Large networks transitioning from older Interior Gateway Protocols (IGPs) like RIP to newer protocols like OSPF benefit from redistribution during migration phases. This gradual approach reduces risk by maintaining connectivity throughout the transition process. Teams can migrate network segments incrementally while preserving end-to-end reachability.

Departmental Network Integration

Organizations where different departments autonomously manage their networks using different protocols require redistribution for inter-departmental communication. This scenario commonly occurs in large enterprises, universities, or organizations with decentralized IT management structures.

IGP to BGP Connectivity

Historically, organizations redistributed internal routes to BGP for Internet advertisement, though network summarization is now preferred. This use case has diminished as best practices evolved toward more controlled route advertisement methods. Modern implementations focus on selective advertisement rather than wholesale redistribution.

Laboratory and Testing Environments

Network engineers use redistribution in lab environments to simulate complex network scenarios and test protocol interactions. This application helps teams understand redistribution behavior before implementing it in production environments.

Advantages and Trade-offs

Route redistribution provides valuable capabilities but introduces significant challenges that require careful consideration.

Advantages

• Interoperability: Redistribution enables communication between disparate routing domains that would otherwise remain isolated. This capability is essential for complex enterprise networks and integration scenarios.
• Flexibility: Organizations can use different routing protocols as needed for specific network segments or applications. This flexibility allows optimization of protocol choice based on network requirements and constraints.
• Gradual Transitions: Redistribution facilitates phased migrations between routing protocols, reducing risk and operational disruption. Teams can transition network segments incrementally while maintaining connectivity.

Trade-offs and Challenges

• Routing Loops: The most significant risk involves routing loops, especially with bi-directional redistribution. Different metrics and Administrative Distance values can create feedback loops that destabilize network operations.
• Suboptimal Routing: Metric translation can cause inefficient traffic paths because metrics are not directly comparable between protocols. A route that appears optimal in one protocol may perform poorly in practice.
• Configuration Complexity: Redistribution requires deep knowledge of all involved protocols and their interactions. Incorrect configuration can cause widespread network instability and difficult-to-diagnose issues.
• Troubleshooting Difficulty: Diagnosing routing issues across redistribution points presents significant challenges. Problems may manifest far from their source, and root cause analysis requires understanding of multiple protocols.
• Advanced Management Requirements: Successful redistribution often requires sophisticated filtering and tagging techniques to control redistributed routes and prevent issues. These techniques add operational complexity.
• Convergence Impact: Poorly implemented redistribution can slow network convergence or create instability during topology changes. The interaction between different convergence algorithms can produce unexpected results.

Key Terms Appendix

• Route Redistribution: The process of injecting routes from one routing protocol into another to enable inter-protocol communication.
• Routing Protocol: A protocol that routers use to exchange routing information, such as OSPF, EIGRP, RIP, or BGP.
• Routing Domain: A set of routers running the same routing protocol and sharing routing information using common algorithms and metrics.
• Redistribution Point (Boundary Router): A router configured to perform redistribution by running multiple routing protocols simultaneously.
• Administrative Distance (AD): A numerical value ranking the trustworthiness of routing sources, used for route selection when multiple protocols provide routes to the same destination.
• Route Metric: A value indicating the “cost” of a path within a specific routing protocol’s metric system.
• Routing Loop: A network condition where packets circulate endlessly due to inconsistent routing information.
• Suboptimal Routing: A situation where traffic takes an inefficient path due to poor route selection or metric translation issues.
• Route Filtering: The process of controlling which routes are advertised or accepted during redistribution.
• Route Tagging: Adding identification tags to routes for policy enforcement and tracking during the redistribution process.
• Routing Information Base (RIB): A router’s comprehensive database containing all known routes from all routing sources.
• Convergence: The state where all routers in a network agree on the current network topology and routing information.
• OSPF (Open Shortest Path First): A link-state Interior Gateway Protocol using cost-based metrics and shortest-path algorithms.
• EIGRP (Enhanced Interior Gateway Routing Protocol): A Cisco proprietary advanced distance-vector IGP using composite metrics based on bandwidth and delay.
• RIP (Routing Information Protocol): A simple distance-vector IGP using hop count as its metric.
• BGP (Border Gateway Protocol): An Exterior Gateway Protocol designed for inter-domain routing between autonomous systems.