Filter small range from bigger advertise range from BGP neighbor

[sefim]

Hi,

I have BGP neighbor that advertise me big network range (51.16.0.0/15) and I would to filter this range and get only smaller range from it (51.17.72.0/22); I want that all the rest of this range continue to go through the default route like as always.

How can I do it?

I tried with prefixlist but it not working because its not the specific range that advertise to me.

This BGP neighbor can't split the bigger range that it advertise me and therefor I should filter it by my self.

I have Fortigate 500E v 6.4.15.

BR,

Sefi

[funkylicious]

Hi,

I guess you are receiving a summarized network from your peer, therefore no specific/smaller networks/prefixes can be filtered out of it.

Without him sending you all the networks, you cannot filter a specific one unfortunately.

You could just deny it/filter it out the /15 network and create a static route for the one that you want.

[sefim]

Hi, thanks for your answer.

I prefer not to use static route because I want to stay with the option to jump the default route if this interface won't working and this range wont advertise through BGP.

[Toshi_Esumi]

51.16.0.0/15 and 51.17.72.0/22 are two separate prefixes although the latter is completely inside of the former. Therefore it is technically NOT "filtering" routes but setting up a new prefix into your routing-table.
If you want it to be dynamic (not static), you have to get it from the source (neighbor). No other way.

Toshi

[sefim]

Thank you