4-4 BGP Configuration Explained

Border Gateway Protocol (BGP) is a critical routing protocol used in large-scale networks, including the internet, to exchange routing information between different autonomous systems (AS). Understanding BGP configuration is essential for network administrators, especially when preparing for the MikroTik Certified Network Associate (MTCNA) certification.

Key Concepts

1. Autonomous Systems (AS)

An Autonomous System (AS) is a collection of IP networks and routers under the control of a single entity that presents a common routing policy to the internet. Each AS is identified by a unique AS number (ASN).

2. BGP Peering

BGP peering refers to the establishment of a BGP session between two routers, allowing them to exchange routing information. Peering can be internal (iBGP) within the same AS or external (eBGP) between different ASes.

3. BGP Routes

BGP routes are the paths that BGP uses to forward packets. These routes are advertised between BGP peers and include attributes such as the AS path, next hop, and local preference.

4. BGP Attributes

BGP attributes are parameters associated with BGP routes that influence the selection of the best path. Common attributes include AS_PATH, NEXT_HOP, LOCAL_PREF, and MULTI_EXIT_DISC (MED).

Detailed Explanation

Autonomous Systems (AS)

Consider an AS as a large company with multiple departments. Each department (network) operates under the same management (AS) and follows the same policies. The company (AS) has a unique identification number (ASN) that distinguishes it from other companies.

BGP Peering

BGP peering is like establishing a communication channel between two companies. If the companies are part of the same organization (iBGP), they share internal information. If they are separate organizations (eBGP), they exchange external information to facilitate business transactions.

BGP Routes

BGP routes are the directions provided to reach a destination. Think of them as maps that guide packets through the network. Each map (route) includes details like the path to follow (AS path) and the next stop (next hop).

BGP Attributes

BGP attributes are the preferences and rules that determine the best route. For example, AS_PATH indicates the sequence of ASes a packet must traverse, while LOCAL_PREF helps in selecting the preferred exit point from an AS.

Examples and Analogies

Example: Autonomous Systems (AS)

Imagine a large university with multiple campuses. Each campus (network) operates under the same administration (AS) and follows the same rules. The university (AS) has a unique ID (ASN) to differentiate it from other universities.

Example: BGP Peering

Consider two neighboring towns that share resources. If they are part of the same county (iBGP), they share internal resources. If they are separate counties (eBGP), they exchange resources to support each other.

Example: BGP Routes

Think of BGP routes as travel itineraries. Each itinerary (route) includes the sequence of cities to visit (AS path) and the next city to stop at (next hop).

Example: BGP Attributes

Consider BGP attributes as travel preferences. For instance, AS_PATH indicates the order of cities to visit, while LOCAL_PREF helps in selecting the preferred exit point from a region.

By mastering 4-4 BGP configuration, you can effectively manage large-scale network routing, ensuring efficient and reliable data transmission.