On Cisco IOS devices, when the aggregate-address summary-only command is applied, the BGP suppressed prefixes are still forwarded, and then they are withdrawn later.
Which command suppresses the BGP aggregated prefixes immediately?
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A. B. C. D.A.
The aggregate-address command in BGP is used to summarize multiple prefixes into a single prefix. When this command is used with the summary-only keyword, it generates only the summary prefix and not the individual prefixes that were summarized. However, the suppressed prefixes are still forwarded to BGP peers and then withdrawn later, which can result in suboptimal routing and unnecessary traffic on the network.
To suppress the suppressed prefixes immediately, the no-advertise-suppressed keyword is used with the aggregate-address command. This keyword causes BGP to suppress the individual prefixes that were summarized, and not forward them to BGP peers at all. This results in optimal routing and reduced traffic on the network.
Option A is incorrect as it refers to the use of a prefix-list to suppress prefixes, which is a different mechanism altogether. It is used to filter prefixes based on their address range, and does not directly relate to the aggregation of prefixes.
Option C is incorrect as it refers to a non-existent command.
Option D is incorrect as it refers to the aggregate-timer command, which is used to control the timing of when the summarized prefixes are advertised, and not to suppress the individual prefixes.
Therefore, the correct answer is option B: aggregate-address summary-only no-advertise-suppressed.