In a BGP routing context, giving these networks address:
192.168.0.0 /28
192.168.0.32 /28
For me, the summary address will be :
192.168.0.0 /26
But someone tells me that this is impossible because at least 192.168.0.16/28 is missing, so i'm wondering if this is possible?
Another example where this is impossible (in his point of view):
192.168.0.0/28
192.168.0.16/28
192.168.0.32/28
For him, this is impossible to summarize because of the lack of 192.168.0.48/28
192.168.0.0000|0000
192.168.0.0001|0000
192.168.0.0010|0000
192.168.0.0011|0000 --because this one is missing
if 192.168.0.48/28 was present, then the summary address will be:
192.168.0.0 /26
Best Answer
Generally speaking, route summarization hides information about more specific routes. It also hides the fact that you may not have a route to all addresses in your summary. So yes, you can summarize. Whether or not you should depends on what you are doing with your summary.
In the case of BGP, you are advertising that you can reach all networks in your summary - but in fact you can't. You will "blackhole" the missing networks because your router will attract traffic for 192.168.0.16/28 (in your example), but you may not actually have a route to that network and you will end up dropping the traffic. If that is OK in your network, then go ahead and summarize.