How does BGP behave differently with auto-summary enabled or disabled?
A. Auto-summary behavior has changed across Cisco IOS software releases. Initially, auto-summary was enabled by default. However, with Cisco bug ID CSCdu81680 ( registered customers only) this behavior has changed. In the latest Cisco IOS, auto-summary is disabled by default. When auto-summary is enabled, it summarizes the locally originated BGP networks to their classfull boundaries. Auto-summary is enabled by default in BGP. When auto-summary is disabled, the routes introduced locally into the BGP table are not summarized to their classfull boundaries. When a subnet exists in the routing table and these three conditions are satisfied, then any subnet of that classfull network in the local routing table will prompt BGP to install the classfull network into the BGP table. • Classfull network statement for a network in the routing table • Classfull mask on that network statement • Auto-summary enabled For example, if the subnet in the routing table is 75.75.75.0 mask 255.255.255.0, and
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