Building the BGP Table - Injecting Routes/Prefixes into the BGP table - Manual Summaries and the AS_PATH Path attribute

9 important questions on Building the BGP Table - Injecting Routes/Prefixes into the BGP table - Manual Summaries and the AS_PATH Path attribute

What are the four different components of the AS_PATH PA?

AS_SEQ (short for AS sequence)
AS_SET
AS_CONFED_SEQ (short for AS Confederation Sequence)
AS_CONFED_SET
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What does the AS_PATH AS_SET segment solve when the summary route has a null AS_SEQ (aggregate-address)? What is the IOS command?

Routing loop. AS_SET has an unordered list off all autonmous sytem. If router notices its own ASN, it will ignores the prefix.

aggregate-address x.x.x.x 255.0.0.0 summary-only AS-SET
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When there's a aggregate address created. Does BGP create a summary when there are no NLRI routes in the BGP table inside the summary?

No

It does not create summary route when BGP table does not have any routes for NLRI inside the summary
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When there's a aggregate address created. How is the NEXT_HOP address listed in the LOCAL BGP table?

It sets the NEXT_HOP address of the summary, as listed in BGP table to 0.0.0.0
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When there's a aggregate address created. How is the NEXT_HOP address advertised to neighbors?

It sets the NEXT_HOP address of the summary route, as advertised to neighbors, to the router's update source IP address for each neighbor
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When there's a aggregate address created and If the component subnets inside the summary differs. How is the summary route's AS_SEQ to be set?

If the AS_SEQ of the component subnets differs in any way, it sets the AS_SEQ of the new summary route to null
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When there's a aggregate address created. What does the router create when the AS-SET command is set?

When the as-set option has been configured, the router creates an AS_SET segment for the aggregate route, but only if the summary route's AS_SEQ is null. This prevents a loop
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When there's a aggregate address created. What does the AS_SET include?

It includes an unordered list of all autonomous systems. When a router recieves a prefix from it's own ASN, it will ignore the prefix. This will prevent a loop.
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When there's a aggregate address created and the summary-only key word is used. What is the behaviour of this command?

It suppressed the advertisement of all component subnets if the summary-only keyword is used, advertises all of them if the summary-only keyword is omitted (weggelaten), or advertised a subset if the suppress-map is confgured
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