BGP - auto-summary best practices

The auto-summary feature in BGP is used to automatically summarize routes at the classful network boundary, causing BGP to advertise the summarized routes of its own networks to its neighbors. The purpose of this command is to simplify the routing table by reducing the number of entries. It is useful in situations where you have very large routing tables and you want to reduce their size.

This of course has advantages and disadvantages, and they must be weighed carefully before using this command.

  • The advantages include a simplification of the routing table, reducing its size, improving efficiency, and simplifying management.
  • Disadvantages include a loss of granularity, and the potential for unintended route advertisements, especially in networks with discontiguous subnets.

So should auto-summary be enabled? Well, it is disabled by default on Cisco routers, so that is an indication of what you should ideally configure. So, if it can be avoided, don't use it. It should only be used if routing tables get too large and CPU and memory of BGP routers are being overly taxed.