Tricky Border gateway protocol[BGT] Multiple choice Questions and Answers pdf

16. What is the difference between Local Preference and MED?
The Local Preference attribute is to influence your own AS how to get or exit to another AS.
MED is to influence other AS how to enter your own AS.

17. What is the command to administratively disable BGP neighborship?
# neighbor neighbor-ip shutdown
# no neighbor neighbor-ip shutdown (to enable it again)

18. Explain BGP Path Attributes?
BGP supports a wide variety of Path Attributes. BGP use these path attributes to examine the competing BGP paths (routes) in BGP table to choose the best path(route).
1. Next Hop - It lists the next-hop IP address used to reach a prefix. If Next hop is reachable? If no route to reach Next Hop, router cannot use this route.
2. Weight - It is a numeric value set by a router when receiving updates to influence the route for a prefix. It is not advertised to any BGP peers. Bigger is preferred
3. Local Preference - It is a numeric value set and communicated within a single AS for the purpose of choosing best route for all routers in that AS to reach a certain network. Bigger is preferred
4. Locally injected routes - Locally injected routes (routes injected using network command) are better than iBGP/eBGP learned.
5. AS Path - It is the number of ASNs in the AS Path. Smaller is preferred.
6. Origin - Preferred I over E & E over ?. It implies that the route was injected into BGP as I (IGP), E (EGP) or ? (incomplete information).
7. Multi-Exit Discriminator (MED) - Allows an AS to tell a neighboring AS the best path to forward packets
into the first AS. Smaller is preferred.
8. Neighbor type - eBGP is preferred over iBGP.
9. IGP metric - Route with nearest IGP neighbor (lowest IGP metric) is preferred.
10. eBGP route - Oldest (longest known) route is preferred.
11. Neighbor Router ID - Lowest is preferred.
12. Neighbor IP address - Lowest is preferred.
Trick to Remember - N WLLA OMNI

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