BGP Path selection

Question 1

What are the first 4 BGP Path selections?

Answer 1

BGP Path selection:
1. BGP Weight = Prefer the path with the highest weight.
2. BGP Local Preference = Prefer the path with the highest local preference.
3. Originate = Prefer the path that the local router originated.
4. AS path length = Prefer the path with the shortest AS path length.

Question 2

What are the last 4 BGP Path selections?

Answer 2

BGP Path selection:

5. AS Path * Most commonly used in real life to select the path in BGP
6. Origin Code
7. MED = multi exit discriminator
8. eBGP path is preferred over iBGP by default

Question 3

What are the path Origin Codes?

Answer 3

Origin Codes:
i = Internally, or IGP
e= externally learned NLRI
? = incomplete, redistribution

Question 4

What’s included in the NLRI packet?

Answer 4

• NLRI stands for “Network Layer Reachability Information.
• NLRI packet = IP Prefix + Prefix Length + Next Hop