BGP: Aggregate Address

The following summarizes the actions taken by the aggregate-address command when it creates a summary route:

  • If  the BGP table does not currently have any routes for NLRI inside the summary it does not create it.
  • If all the component routes are removed from the aggregating router’s BGP table, it will also remove the aggregate route.
  • It sets next hop to 0.0.0.0 for the summary route in the local BGP table
  • It sets the next hop address of the advertised summary route to the aggregating routers update-source IP for each neighbor respectively.
  • If the component routes AS_SEQ all match, the aggregating router will set the same AS_SEQ to the summary route
  • If the AS_SEQ is different for any component route, the aggregating router will set the summary route to null AS_SEQ
  • If the summary is advertised to a peer, the router prepends its own ASN to the AS_SEQ before sending the update.
  • It suppresses the advertisement of component networks if the summary-only keyword is used, will advertise all component routes if it’s not used, and will only advertise a subset of routes if the suppress-map option is configured.

 

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