BGP - Preventing the AS from advertising local net

Hi GS,

assume there is one AS with the network 172.16.0.0/24
Also there are 2 other AS's

What is the best practice to prevent _only_ this network to advertise to the BB routers ?

router bgp 33
 neighbor x.x.x.x remote-as 33
 neighbor x.x.x.x send-community both
 neighbor x.x.x.x route-map PREV out

ip prefix-list prevent seq 5 172.16.0.0/24

route-map PREV
 match ip address prefix-list prevent
 set community no-advertise

THis soulution prevent the local net to send to the neighbor..

Right now my problem is I doesn't understand why...;-)
Because I thought the community no-advertise is send to the _next_ AS and prevent the specific prefix to send outr the neighbor AS ?!?!

Please can anyone explain me if this a normal behaviour...

Thanks

Dennis

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