BSCI – BGP Pt.3

What does the greater-than sign (>) mean inthe output of the show ip bgp command?
The greater-than sign indicates the best path for a route selected by BGP. This is the route that is offered to the IP routing table.
What command is used to display the BGP routes that were not installed in the RIB?
show ip bgp rib-failure
What command displays the status of all BGP connections?
show ip bgp summary
What command is used to view BGP updates as they’re being sent?
debug ip bgp updates
What are the different neighbor states that a BGP neighbor can be in?

– Idle – The router is searching the routing table to see whether a route exists to reach the neighbor.

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– Connect – The router found a route to the neighbor and has completed the 3-way TCP handshake.

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– Open sent – An open message was sent, with the parameters for the BGP session.

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– Open confirm – The router received agreement on the parameters for establishing a session.

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– Active – The router goes into active state if it doesn’t receive a response to an open message

 

– Established – Peering is established and routing begins. 

What command is used to display information about the BGP connections to neighbors?
show ip bgp neighbors
What command is used to change the default local preference for all BGP routes advertised by a router?
bgp default local-preference value
What command can be used to change the default MED value on a BGP router?
default-metric value
What command is used to assign a weight to updates from a neighbor connection?
neighbor {ip-address | peer-group} weight value
Describe the 2 BGP attributes that are related to aggregate addressing.

– Atomic aggregate – A well-known disctretionary attribute that informs the neighbor AS that the originating router has aggregated the routes.

 

– Aggregator – An optional transitive attribute that specifies the BGP router ID and AS number of the router that preformed the route aggregation. 

How does BGP handle redistribution when summarization is enabled?
When summarization is enabled (with auto-summary), all redistrbuted subnets are summarized to their classful boundaries in the BGP table. When summarization is disabled, all redistributed subnets are present in their original form in the BGP table.
What command is used to create an aggregate, or summary, entry in the BGP table?
aggregate-address ip-address mask [summary-only] [as-set]
When summarizing routes in BGP, what is the difference between using the network command and using the aggregate-address command?
The network command only advertises summaries that already exist in the IP routing table. With the aggregate-address command aggregates only networks that are already in the BGP table.
What command is used to create a prefix list?
ip prefix-list {list-name | list-number} [seg value] {permit | deny} network/length [ge value] [le value]
What command is used to filter BGP neighbor information as specified in a prefix list?
neighbor {ip-address | peer-group} prefix-list list-name {in | out}
What command is used to add a text description for a prefix list?
ip prefix-list list-name description text
What command is used to display detailed information about all prefix-lists?
show ip prefix-list [detail | summary]
What command is used to display detailed information about a specific prefix-list?
show ip prefix-list [detail | summary] prefix-list-name
What are the different ways that a community number can be defined?
The community value can be entered as one decimal number or in the format of AS:nn, where the AS is the autonomous system number, and nn is the lower 16-bit local number.
What command is used within a route map to set the BGP community attribute?
set community {[community-number] [well-known-community] [additive]} | none
What command is used to specify that the BGP communities attribute should be sent to a BGP neighbor?
neighbor {ip-address | peer-group} send-community
What is the default behavior for a router looking to send out a community attribute?
By default, the communities attribute is not sent to any neighbors, since communities are stripped in outgoing BGP updates.
What command is used to create a community list for BGP and to control access to it?
ip community-list list-number {permit | deny} community-number
Describe the basic use of route reflectors.
A route reflector is a router that is configured to be the router allowed to advertise (reflect) routes it learned vian IBGP to other IBGP peers.
How does a route reflector handle updates that it receives?
If the update if from a client peer, or from an EBGP peer, it sends the update to all nonclient and client peers (except the route’s originator). But if the update is from a nonclient peer, it sends the update to all clients in the cluster.
What command allows you to configure a router as a BGP RR and to configure the specified neighbor as its client?
neighbor ip-address route-reflector-client
What command is used to configure a cluster ID for a RR?

bgp cluster-id cluster-id