Missing route that is shown in filter used by eBGP

[Maria Matejka]

Hello Nico,

unless you have BGP TX Add-Path, you are exporting only the best route,
which is the direct one in this case, and that's filtered out.

I would suggest to drop the direct protocol preference under the static
protocol, at least for this route.  Or raising the preference in the
static, you may say something like

    route 185.203.114.0/23 dev eth4 { preference = 250; };

for just this one route and i hope that i haven't botched our own syntax.

This should make it work.

Maria

On Thu, Nov 20, 2025 at 01:59:48PM +0100, Nico Schottelius via Bird-users wrote:

> Hello,
> 
> today I have a related issue with missing route export:
> 
> - In a bgp instance I use the filter "from_our_place_to_internet"
> - If I run "show route filter from_our_place_to_internet" all correct
>   routes match
> - However if I check on the other eBGP end, the route is actually *not*
>   received (it's not filtered, it is really not received)
> - If I "hack" the filter as follows, bird DOES export the route:
>   # Hack 2025-11-20
>   if ( net ~ [ 185.203.114.0/23+ ] ) then {
>      print "Exporting 185.203.114.0 to internet";
>      accept;
>   }
> 
> - Some thoughts:
>   - The route is direct, static and babel received
>   - Our filter matches RTS_STATIC
>   - However bird seems to "prefer" the direct route
>   - We do not export direct marked routes, but static routes
>   - Is that the cause of the problem? But it is also static...
> 
> However it does not make sense to me, thus wondering:
> 
> - Why does bird show the route in the filter output?
> - Why does bird show not export it via eBGP?
> - Why does my hack then make it work in the end?
> 
> 
> Details below, any help appreciated as this is driving me nuts.
> 
> Best regards,
> 
> Nico
> 
> --------------------------------------------------------------------------------
> 
> a) the affected route
> 
> bird> show route all 185.203.114.0/23
> Table master4:
> 185.203.114.0/23     unicast [direct1 2025-11-07] * (240)
>         dev eth4
>         Type: device univ
>                      unicast [place6_10_v4 2025-11-07] (200)
>         dev eth4
>         Type: static univ
>                      unicast [babel1 12:47:44.565 from fe80::3eec:efff:fecb:d81b] (130/96) [00:00:00:00:93:4e:c2:43]
>         via 147.78.194.67 on eth1
>         Type: Babel univ
>         Babel.metric: 96
>         Babel.router_id: 00:00:00:00:93:4e:c2:43
> bird>
> 
> b) the show route output
> 
> bird> show route filter from_our_place_to_internet
> Table master4:
> 185.203.114.0/23     unicast [place6_10_v4 2025-11-07] (200)
>         dev eth4
> ...
> 
> 
> c) the filter itself
> 
> filter from_our_place_to_internet {
>   if(!has_internet_length()) then reject;
>   if(is_default_route()) then reject;
> 
> 
>   if(is_from_local_asn() ||
>      is_emitted_by_one_of_our_asn_directly() ||
>      should_export_to_internet_from_customer()
>      ) then accept;
> 
>   reject;
> 
> }
> 
> ... where the related functions are:
> 
> 
> function has_internet_length() -> bool
> {
>   if ((net.type = NET_IP6 && net.len > 48) ||
>       (net.type = NET_IP4 && net.len > 24)) then {
>           return false;
>   }
>   return true;
> }
> 
> function is_v6_default() -> bool
> {
>   if (net = ::/0) then return true;
>   return false;
> }
> 
> function is_v4_default() -> bool
> {
>   if (net = 0.0.0.0/0) then return true;
>   return false;
> }
> 
> function is_default_route() -> bool
> {
>   if(is_v6_default() || is_v4_default()) then return true;
>   return false;
> }
> 
> function is_from_local_asn() -> bool
> {
>   if(source = RTS_STATIC) then return true;
>   if(source = RTS_BGP && bgp_path.len = 0) then return true;
> 
>   return false;
> }
> 
> function emitted_from_one_of_our_asn() -> bool
> {
>   if(bgp_path.last ~ our_asn) then return true;
>   return false;
> }
> 
> function should_export_to_internet_from_customer() -> bool
> {
>   # We don't consider non-internet networks
>   if(!has_internet_length()) then return false;
> 
>   if (
>      (bgp_path.first ~ our_asn) &&   # received from one of our asn
>      (bgp_path.len = 2)         &&   # one of our ASNs received it
>      (bgp_path.last ~ customer_asn)  # one of our customers emitted it and we accept it
>      ) then return true;
> 
>    if (
>       (bgp_path.len = 1)         &&   # we ASNs received it directly
>       (bgp_path.last ~ customer_asn)  # one of our customers emitted it and we accept it
>       ) then return true;
> 
>    return false;
> }
> 
> 
> --
> Sustainable and modern Infrastructures by ungleich.ch

-- 
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
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