On March 26, 2019 10:34:39 AM GMT+01:00, Alexander Zubkov <green@qrator.net> wrote:

Hi,

You can try to delete AS-TRANSIT from the path and get first.
Something like (this is just a sketch):

delete(bgp_path, AS-TRANSIT).first ~ BOGON_ASNS

On Mon, Mar 25, 2019 at 9:50 PM Robert Scheck <bird@robert-scheck.de> wrote:

 Hello folks,

 can I somehow import filter only on the 2nd AS number in the AS path? I
 know with the snippet below (heavily inspired by bgpfilterguide.nlnog.net),
 I can filter on AS numbers that appear somewhere in the AS path, however
 this import filter catches by nature also some pseudo-legitimate networks.

 define BOGON_ASNS = [ 0, 23456, 64496..64511, 64512..65534, 65535, 65536..65551, 65552..131071, 4200000000..4294967294, 4294967295 ];

 if (bgp_path ~ BOGON_ASNS) then {
   print "Detected bogon AS path: ", net, " ", bgp_path, ", (neighbour ", from, ")";
 }

 There are unfortunately some transits with broken export filters which e.g.
 export their DSL/FTTC and FTTH networks using private ASNs and I would like
 to explicitly filter these (example path: AS-TRANSIT AS-BOGON1 AS-BOGON2).

 The documentation has hints for first and last ASN in path, but this would
 catch in above example only AS-TRANSIT or AS-BOGON2, but not AS-BOGON1. Any
 pointers?

 Thank you.


 Regards,
   Robert