Cisco CCNP BSCI Certification The Local Preference BGP Attribute
Below is a MRR and PLR article in category Computers Technology -> subcategory Computer Certification.
Cisco CCNP/BSCI Certification: Mastering the Local Preference BGP Attribute
Summary:
Discover how to effectively use the BGP Local Preference attribute to excel in your BSCI exam with insights from Chris Bryant, CCIE12933.
Article:
When preparing for the BSCI exam as part of your CCNP certification, you'll encounter BGP (Border Gateway Protocol) for the first time. Unlike other protocols you've studied, BGP utilizes attributes to define paths and influence path decisions.
In this guide, we'll explore the Local Preference attribute and compare it with the Cisco-proprietary attribute "weight."
Understanding Local Preference
The Local Preference (LOCAL_PREF) attribute plays a crucial role in determining how traffic flows between Autonomous Systems (AS) when multiple paths are available. For instance, if AS 100 has two pathways to a destination network in AS 200, the LOCAL_PREF attribute can decide which path to prioritize.
Local Preference vs. Weight
A key distinction between the Weight and LOCAL_PREF attributes is their scope of influence. Changes to the LOCAL_PREF attribute are propagated throughout the AS, impacting all routers within the AS. On the other hand, changes to the Weight attribute are locally significant, affecting only the router where the change occurs.
Modifying Local Preference with a Route-Map
To modify the local preference value for a specific path, follow these steps:
1. Create an Access Control List (ACL): This ACL will match the network for which you wish to change the local preference.
```plaintext
R1(config)
access-list 5 permit 10.2.2.0 0.0.0.255
```2. Set Up a Route-Map: Use a route-map to adjust the local preference to 200, doubling the default value of 100. The path with the highest local preference is selected.
```plaintext
R1(config)
route-map PREFER_PATH permit 10
R1(config-route-map)match ip address 5
R1(config-route-map)set local-pref 200
```3. Apply the Route-Map: Implement the route-map on routes received from the neighbor 10.1.1.1.
```plaintext
R1(config)
router bgp 100
R1(config-router)network 10.1.1.1 route-map PREFER_PATH in
```R1 will then broadcast this updated local preference to all its iBGP neighbors within AS 100.
By mastering the Local Preference attribute, you can effectively influence path selection in BGP, enhancing both your network's performance and your chances of success in the BSCI exam.
You can find the original non-AI version of this article here: Cisco CCNP BSCI Certification The Local Preference BGP Attribute.
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