The AS-path policy for this eBGP neighbor is receive/send routes with maximum 3 AS paths away from/to us/customer. The issue is we found out from traffic analysis that this neighbor also route traffic beyond the 2 AS paths away from us. In other words, we have become transit without any intention to be that and without our permission.
The only possible solution that I can think of is my eBGP router that peering to that eBGP neighbor should have only BGP routes that have maximum 2 AS paths and no default route in IP routing table. So, traffic with destination beyond IGP and 2 AS paths away will be dropped by my router.
Any other solution? It seems impossible with access list.