Fundamentals of BGP Operations - Building the BGP Table - Injecting Routes/Prefixes into the BGP table

12 important questions on Fundamentals of BGP Operations - Building the BGP Table - Injecting Routes/Prefixes into the BGP table

How does the individual BGP router entries to its local database? 3

-Network command
-Topology information through an update message from a neighbor
-Redistributing from other routing protocol
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What can the BGP redistribute subcommand redistribute? 3

-redistribute static
-connected
-IPG learned routes
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What does BGP assign when a route with a metric is injected to BGP?

BGP assigns metric value from routing protocol to the BGP Multi-Exit Discriminator (MED) PA
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What is the impact of the auto-summary command on redistribute routes?

If any subnets of a classfull network would be restribute, do not redistribute, but instead redistribute a route for the classfull network
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What is the impact of the auto-summary command on the network command?

if a network command lists a classful network number, with the classful default mask or no mask, and any subnets of the classful network exists, inject a route for the classful network.
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When you inject a default route into BGP using network command. What is required?

0.0.0.0/0 must exist in routing table
(config-router)#network 0.0.0.0 is required
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What does the command Neighbor neighbor-id default-originate [route-map route-map-name] do?

Does not add default route to local BGP table
Add default route to specific neighbor

With route-map option, the reference route-map examines entries  in the IP routing table, if a route map clause is matched the default route is advertised to the neighbor.
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What are the three main parts of the BGP update message?

-The Withdrawn (teruggetrokken) routes field enables BGP to inform its neighbors about failed routes
-Path Attributes field lists PA for each route (NEXT_HOP and AS_PATH)
-Prefix and Prefix lengt field (NLRI)
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When are separated BGP update messages necessay?

When there's at least one different PA for a NLRI
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What does the output column State/PfxRcd mean using the command show ip bgp summary command?

Number of NLRI's recieved from neighbor
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Each BGP route's NEXT_HOP must be reachable for a route to be truly valid.
How can you configure this for iBGP?

-Make the eBGP neighbor's address reachable by advertising that subnet into the IGP
-Use the next-hop-self option on the neighbor command that points to iBGP peers
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What are the rules for a BGP router to send routes in its update messages? 4

-Send only the best route listed in the BGP table
-To ibgp neighbors, do not advertise paths learned form other iBGP neighbors
-Do not advertise suppressed or dampened routes
-Dot not advertise routes filtered through configurations
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