BGP Routing Concepts Quiz

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Questions and Answers

What is the primary purpose of the aggregate-address command in BGP?

To manually specify AS-path attributes for routes

To ensure routes are advertised in their most specific form

To create an aggregate entry in the BGP table (correct)

To configure individual routes for BGP speakers

Which of the following statements about the ATOMIC_AGGREGATE attribute is correct?

It indicates that a specific route has been sent without including more specific details. (correct)

It automatically advertises both specific and aggregate routes.

It is mandatory for BGP updates that contain summarized routes.

It specifies the exact routes contained in the aggregate update.

When a router receives overlapping routes, which one does it prefer during the best path selection?

The less-specific route

The route with the lowest metric value

The more-specific route (correct)

The route with the longest AS-path

What happens if a BGP speaker advertises an aggregate route without including the more-specific routes?

The ATOMIC_AGGREGATE attribute will be set to True. Signup and view all the answers

In BGP, which technique allows for combining multiple route advertisements into a single summary route?

Route summarization Signup and view all the answers

Which command syntax correctly represents the usage of aggregate-address in BGP?

Router(config-router)# aggregate-address address mask Signup and view all the answers

What is the effect of advertising the less-specific route in link aggregation?

Draining of traffic may occur on more specific paths. Signup and view all the answers

Which of the following is NOT a potential option when advertising overlapping routes?

Advertise routes based on the lowest metric Signup and view all the answers

What command is used to deny a specific prefix in a prefix-list?

ip prefix-list list-name [seq seq-value] deny Signup and view all the answers

What is the purpose of the default-originate option in BGP?

To specifically send default information to a designated neighbor Signup and view all the answers

How can a BGP router advertise a default route to all peers?

Using the network command as 'network 0.0.0.0' Signup and view all the answers

What does multihoming in an Autonomous System (AS) typically lead to?

Asymmetrical traffic flows Signup and view all the answers

Why is it important to control default information in BGP?

To prevent misadvertisements leading to routing issues Signup and view all the answers

What is the effect of static default routes compared to dynamically learned routes?

More predictable routing decisions Signup and view all the answers

What command can be used to check the entries in an IP prefix list?

show ip prefix-list Signup and view all the answers

What is an atomic aggregate in BGP?

A method to summarize multiple routes into one Signup and view all the answers

What is the purpose of the 'aggregate-address' command in BGP?

To create a summarized route from overlapping routes Signup and view all the answers

Which attribute is considered well-known mandatory in BGP?

AS_PATH Signup and view all the answers

What does the 'set metric' command do within a route map?

Overrides the default path selection criteria Signup and view all the answers

In the context of BGP path attributes, which attribute is optional non-transitive?

MULTI_EXIT_DISC Signup and view all the answers

How does the 'bgp always-compare-med' command affect MPLS traffic?

It ensures all BGP paths consider the MED attribute equally. Signup and view all the answers

What role does the ATOMIC_AGGREGATE attribute serve in BGP routing?

To combine multiple routes into a single route advertisement Signup and view all the answers

Which router configuration correctly sets up a BGP neighbor relationship?

router bgp 400; neighbor 4.4.4.4 remote-as 100 Signup and view all the answers

What is the intended use of the COMMUNITY attribute in BGP configurations?

To signal the routing policy to be applied Signup and view all the answers

Study Notes

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.

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Description

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.