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Why there is a Warning (The number of routes configured does not fit in the address range.) after config the Route Generator of BGP on Spirent TestCenter (STC).


In Spirent TestCenter Application, if you Config the BGP Route Generator with 100000 routes and 10% duplicate with Prefix length Distribution type: internet. you may find following warning:

BGP Route Generator Summary Information

    Primary IPv4 Routes: 100000
    Secondary IPv4 Routes: 9997   (10000 configured)


The number of routes configured does not fit in the address range.
    The maximum allowed routes were created instead.

Some may ask why the secondary IPv4 routes is 9997 not 10000? This is caused by the calculation. For the "internet" distribution, the prefix length is not fixed, for example, you may have 200 route with prefix length 30, so the secondary route number is 20. But if you may also have 299 route with prefix length 32, and the secondary route number is 29 not 29.9! So you see we miss almost 1 route already, and in the whole 100000 routes, you have3 secondary routes less than expected. This is normal situation.

Product : Spirent TestCenter,BGP