BGP Routing Concepts Quiz

Chapter 9 - BGP (Part 2)

• CCNP 1 version 3.0, thanks to Rick Graziani
• Common BGP attributes include Next Hop, AS_Path, Atomic Aggregate, Aggregator, Local Preference, Weight, Multiple Exit Discriminator (MED), and Origin.
• Altering routes changes traffic behavior. Understanding how to prevent private networks from advertising, filter routing updates from specific neighbors, and prioritize certain links/providers is crucial.

Implementing Policy

• Traffic inside and outside an Autonomous System (AS) adheres to the defined route map.
• Modifying the route map directly impacts the network traffic behavior.

Using BGP Attributes

• When receiving updates for the same destination from multiple autonomous systems, BGP chooses the best path.
• The best path is selected based on various attributes (such as Next_Hop) and configurable BGP factors.
• Once chosen, the best path is then propagated to the neighbors.

Commands for BGP Routing Table

• show ip bgp EXEC command is used to display entries in the BGP routing table.
• Options like [network], [network-mask], and [longer-prefixes] can be combined for more specific viewing.

BGP Table Details

• BGP table version, local router ID, status codes (e.g., suppressed, damped), and origin codes (e.g., IGP, EGP) are displayed.
• The Network, Next Hop, Metric, LocPrf, Weight, and Path attributes are crucial in understanding BGP routes.
• Attributes such as the Origin code, and the status codes are useful when diagnosing BGP issues.

Path Attributes

• Various attributes with their corresponding codes (e.g. ORIGIN, NEXT_HOP, AS_PATH, LOCAL_PREF, Weight, MULTI_EXIT_DISC (MED), ATOMIC_AGGREGATE) define the path of a route.
• Multiple options for attributes are noted to grasp basic concepts first, for further information.
• The ORIGIN attribute determines the origin of a route (IGP, EGP, or INCOMPLETE).
• The NEXT_HOP attribute, vital in forwarding a packet, is analyzed in detail for both EBGP and IBGP scenarios.
• The importance of the AS_PATH attribute and how it expresses which AS numbers a route has traversed is explained.
• The attribute 'Metric' is an inter-autonomous system metric.
• The attribute 'Local Preference' is a configurable value.
• The attribute 'Weight' acts as a weight of a route as defined via autonomous system filters.
• The attribute 'Path' represents the autonomous system paths to the destination network
• Origin codes indicate the origin of the routes.

Summary of the BGP Path Selection Process

• BGP selects only one path as the best path.
• Criteria for path selection (in order): inaccessibility of next hop, largest weight, largest local preference, AS origin if none was originated, shortest AS_path if all AS paths are equal, lowest origin type, lowest MED attribute, external path over internal paths if MED is equal, the closest IGP neighbor, lowest IP address as specified by the BGP router ID.

BGP Attributes (Specific)

• ORIGIN attribute: Well-known mandatory, indicates the origin (IGP, EGP, or incomplete).
• NEXT HOP: Well-known mandatory, IP address of the next hop used to reach a destination.
• AS PATH: Well-known mandatory, sequence of AS numbers a path traverses to a destination.
• LOCAL PREF: Well-known discretionary, used to increase the preference of a route for the same destination.
• WEIGHT: Well-known discretionary, used to manipulate path selection.
• MULTI_EXIT DISC (MED): Optional Non-Transitive, provides a hint about the preferred path.

Configuration for manipulating BGP Attributes

• Use route maps and the set origin command to alter the ORIGIN attribute.
• Multiple configurable parameters are for further information and reference.

Test your knowledge on BGP routing concepts with this quiz. It covers important topics such as the aggregate-address command, route selection preferences, and techniques for advertising routes. Perfect for students and professionals looking to solidify their understanding of BGP.