Filter small range from bigger advertise range from BGP neighbor

4 replies
1128 views

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

SuperUser

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.

"jack of all trades, master of none"

sefimAuthor

New Member

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

SuperUser

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

sefimAuthor

New Member

Thank you

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