3V0-25.25 practice question 2 of 15

An administrator is configuring Border Gateway Protocol (BGP) routing on a Tier-0 Gateway to optimize north—south traffic flow between the NSX…

Choose your answer, then check it against the explanation.

An administrator is configuring Border Gateway Protocol (BGP) routing on a Tier-0 Gateway to optimize north—south traffic flow between the NSX environment and multiple upstream physical routers. The environment includes two external connections that advertise overlapping routes to the same destination networks. To ensure predictable and efficient routing behavior, the administrator decides to manipulate specific BGP attributes on outbound advertisements and inbound route updates. What are two valid BGP Attributes that can be used to influence the route path traffic will take? (Choose two.)

Answer options

Correct Answer:

C, D

Explanation

To influence BGP route path selection, administrators manipulate BGP attributes. AS-Path Prepend is used on outbound route advertisements to artificially lengthen the ASPATH attribute. Since BGP prefers shorter paths, this makes the advertised route less preferable to external peers, influencing inbound traffic flow away from that path. The Multi-Exit Discriminator (MED) attribute is also advertised to an external peer to influence how that peer sends traffic into the local AS when multiple entry points exist. A lower MED value is preferred, making it the chosen path for inbound traffic. Both are standard BGP traffic engineering mechanisms available on an NSX Tier-0 Gateway.

Why Incorrect

A. BFD: Bidirectional Forwarding Detection (BFD) is a protocol used for rapid failure detection of the forwarding path, not a BGP attribute for path selection.

B. Cost: Cost is a metric used by Interior Gateway Protocols (IGPs) like OSPF to determine the best path within an autonomous system, not a standard BGP attribute.

References

1. VMware NSX Documentation

"Route Maps on Tier-0 Gateways": This official document details the configuration of route maps on Tier-0 gateways to manipulate BGP updates. It explicitly lists set as-path-prepend and set med as available actions to influence routing decisions. (Search for "Route Maps on Tier-0 Gateways" in the VMware NSX product documentation for the relevant version).

2. VMware NSX Documentation

"Add a Tier-0 Gateway": In the section describing BGP configuration for a Tier-0 gateway

the documentation outlines the use of route maps for filtering and modifying BGP advertisements

which includes setting attributes like AS-Path and MED for traffic engineering. (Search for "Configure BGP on a Tier-0 Gateway" in the VMware NSX product documentation).

3. VMware NSX Reference Design Guide: This guide discusses north-south connectivity patterns and often details best practices for traffic engineering using BGP. It describes using AS-Path prepending and MED to influence inbound traffic routing from upstream physical routers to the NSX environment. (Refer to the BGP routing design sections in the latest NSX Reference Design Guide).

Question 2 of 15

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