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.