changing bgp_med attributes cause route been filited

20 Jul 2023

      Hi all,

I was doing research about selecting the best route on multiple nodes based
on bgp_med attributes.

function ibgp_import(int bgp_med_ping; int extra_bgp_med){
            add_type("ibgp");
            if is_bogon_asn() then {
                print "is bogon asn", net, " for ASN ", bgp_path.last;
                return false;
            }
            if is_bogon_prefix() then {
                print "is bogon prefix", net, " for ASN ", bgp_path.last;
                return false;
            }

            if (LOCAL_ASN, 47, NODE_ID) ~ bgp_large_community then {
            reject;
            }

            if bgp_large_community ~ [(LOCAL_ASN, 2, 100)] then preference
= 115;
            additional_import_action();
            bgp_med = bgp_med + bgp_med_ping + bgp_med_ping;
                return true;
}

My idea is to add bgp_med value between each node based on ping, and then
bird will select the route which has the lowest bgp_med value (which is the
total ping delay)

But some routes will be filled, which i don't want it.

I found that the code " bgp_med = bgp_med + bgp_med_ping + bgp_med_ping;"
will cause some routes to be filtered.

Can someone tell me why? I only want to modify bgp_med and don't want my
routes to be filtered.

Best,
*Brandon Zhi*
HUIZE LTD
www.huize.asia  <https://huize.asia/>| www.ixp.su | Twitter

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