3-2-3 Routing Policy Design

Key Concepts

• Routing Policies
• Prefix Lists
• Route Maps
• Community Lists
• BGP (Border Gateway Protocol) Policies

Routing Policies

Routing Policies are rules and configurations that determine how routers select and forward routes. They are essential for controlling traffic flow, optimizing network performance, and ensuring security. Routing policies can be applied to various routing protocols, such as OSPF, EIGRP, and BGP.

Example: A routing policy might dictate that traffic destined for a specific subnet should be routed through a particular path to optimize latency and avoid congested links.

Prefix Lists

Prefix Lists are used to filter routes based on IP address prefixes. They allow network administrators to define which routes should be allowed or denied based on their prefix length and specific IP ranges. Prefix lists are often used in conjunction with route maps to enforce routing policies.

Example: A prefix list might be configured to allow only routes with a prefix length of /24 or shorter, ensuring that more specific routes are not accepted into the routing table.

Route Maps

Route Maps are a powerful tool for applying complex routing policies. They consist of a series of match and set statements that allow administrators to filter routes based on various criteria and modify route attributes. Route maps are commonly used in BGP to control route advertisements and preferences.

Example: A route map might be used to match routes with a specific community value and set a higher local preference, ensuring that those routes are preferred over others in the routing table.

Community Lists

Community Lists are used to classify routes based on community attributes. Communities are tags that can be attached to BGP routes to indicate their origin or purpose. Community lists allow administrators to apply routing policies based on these tags, enabling more granular control over route selection and advertisement.

Example: A community list might be used to match routes with a community value indicating that they originate from a specific data center. These routes can then be prioritized or filtered based on the defined policy.

BGP (Border Gateway Protocol) Policies

BGP Policies are routing policies specifically applied to the BGP protocol. BGP is a path-vector routing protocol used to exchange routing information between autonomous systems (ASes) on the internet. BGP policies allow administrators to control how routes are advertised, received, and preferred within the network.

Example: A BGP policy might be configured to prefer routes that traverse a specific AS path, ensuring that traffic is routed through a preferred provider or avoiding certain ASes known for poor performance.

Examples and Analogies

Think of Routing Policies as traffic rules that guide how vehicles (data packets) move through a city (network). Prefix Lists are like street signs that indicate which roads (IP prefixes) are open or closed. Route Maps are like traffic lights that control the flow of vehicles based on specific conditions.

Community Lists are like vehicle stickers that indicate the origin or purpose of the vehicle, allowing traffic officers (routers) to apply specific rules based on these tags. BGP Policies are like international traffic agreements that determine how vehicles can travel between different countries (ASes).

By understanding these key concepts, network professionals can design and implement effective routing policies that optimize network performance, ensure security, and meet the needs of modern enterprises.