BIRD 2.0.{7,10} MED not actually send for learned routes if export table on is set

[Inrin]

Addendum:
Using iBGP with export tables and setting the MED works.

On Sun, Oct 16, 2022 at 11:17:23AM +0200, Inrin via Bird-users wrote:
>Greetings,
>
>I noticed during setting up a peering that the MED is not actually send
>to my peer, although bird shows it in the export.
>We confirmed this via tcpdump on both ends.
>
>After debugging a bit, I noticed that this only affects “learned” routes
>but routes from the static protocol worked just fine.
>
>After disabling the “export table” feature, the MED was send out just
>fine.
>
>Is this behaviour expected?
>
>This behaviour is reproducible in BIRD 2.0.7 and 2.0.10 with the
>following scenario (Configs to test are attached):
>
>	R0 is connected to R1 and R2
>	R0, R1 and R2 send each one route
>	R0 sets the MED to 300
>	R1 sets the MED to 100
>	R2 sets the MED to 200
>
>Setting “export table on;” yields the following results:
>
># Bird shows the MED in the export
>R0 $ ./birdc s r all export R1
>BIRD 2.0.10 ready.
>Table master4:
>198.18.0.0/24       unicast [static1 02:05:56.604] * (200)
>        Type: static univ
>        BGP.med: 300
>198.18.2.0/24       unicast [R2 02:11:51.132 from 198.19.0.2] * (100) [AS4242420002i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420002
>        BGP.next_hop: 198.19.0.2
>        BGP.med: 300
>        BGP.local_pref: 100
>R0 $ ./birdc s r all export R2
>BIRD 2.0.10 ready.
>Table master4:
>198.18.0.0/24       unicast [static1 02:05:56.604] * (200)
>        Type: static univ
>        BGP.med: 300
>198.18.1.0/24       unicast [R1 02:11:51.133 from 198.19.0.1] * (100) [AS4242420001i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420001
>        BGP.next_hop: 198.19.0.1
>        BGP.med: 300
>        BGP.local_pref: 100
>R0 #
>
>But on R1, R2 it does not appear for learned routes:
>R1 $ ./birdc s r all protocol R0
>BIRD 2.0.10 ready.
>Table master4:
>198.18.0.0/24       unicast [R0 02:11:51.133 from 198.19.0.0] * (100) [AS4242420000i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420000
>        BGP.next_hop: 198.19.0.0
>        BGP.med: 300
>        BGP.local_pref: 100
>198.18.2.0/24       unicast [R0 02:11:51.133 from 198.19.0.0] * (100) [AS4242420002i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420000 4242420002
>        BGP.next_hop: 198.19.0.0
>        BGP.local_pref: 100
>R1 $
>
>R2 $ ./birdc s r all protocol R0
>BIRD 2.0.10 ready.
>Table master4:
>198.18.0.0/24       unicast [R0 02:11:51.132 from 198.19.0.0] * (100) [AS4242420000i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420000
>        BGP.next_hop: 198.19.0.0
>        BGP.med: 300
>        BGP.local_pref: 100
>198.18.1.0/24       unicast [R0 02:11:51.133 from 198.19.0.0] * (100) [AS4242420001i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420000 4242420001
>        BGP.next_hop: 198.19.0.0
>        BGP.local_pref: 100
>R2 $
>
>
>Setting “export table off;” yield the expected result:
>R1 $ ./birdc s r all protocol R0
>BIRD 2.0.10 ready.
>Table master4:
>198.18.0.0/24       unicast [R0 03:15:47.147 from 198.19.0.0] * (100) [AS4242420000i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420000
>        BGP.next_hop: 198.19.0.0
>        BGP.med: 300
>        BGP.local_pref: 100
>198.18.2.0/24       unicast [R0 03:15:50.635 from 198.19.0.0] * (100) [AS4242420002i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420000 4242420002
>        BGP.next_hop: 198.19.0.0
>        BGP.med: 300
>        BGP.local_pref: 100
>R1 $
>
>R2 $ ./birdc s r all protocol R0
>BIRD 2.0.10 ready.
>Table master4:
>198.18.0.0/24       unicast [R0 03:15:50.635 from 198.19.0.0] * (100) [AS4242420000i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420000
>        BGP.next_hop: 198.19.0.0
>        BGP.med: 300
>        BGP.local_pref: 100
>198.18.1.0/24       unicast [R0 03:15:50.635 from 198.19.0.0] * (100) [AS4242420001i]
>        Type: BGP univ
>        BGP.origin: IGP
>        BGP.as_path: 4242420000 4242420001
>        BGP.next_hop: 198.19.0.0
>        BGP.med: 300
>        BGP.local_pref: 100
>R2 $

>protocol static { route 198.18.0.0/24 reject; ipv4 {}; }
>template bgp rs_peers {
>  local 198.19.0.0 port 1179 as 4242420000;
>  ipv4 {
>    import table off;
>    export table on;
>    import all;
>    export filter {
>      if source ~ [RTS_STATIC, RTS_BGP] then {
>	bgp_med = 300;
>        accept;
>      }
>      reject;
>    };
>  };
>};
>
>protocol bgp R1 from rs_peers {
>  neighbor 198.19.0.1 port 1179 as 4242420001;
>};
>protocol bgp R2 from rs_peers {
>  neighbor 198.19.0.2 port 1179 as 4242420002;
>};

>protocol static { route 198.18.1.0/24 reject; ipv4 { }; }
>protocol bgp R0 {
>  ipv4 {
>    import all;
>    export filter {
>      if source ~ [RTS_STATIC, RTS_BGP] then {
>	bgp_med = 100;
>        accept;
>      }
>      reject;
>    };
>  };
>  local 198.19.0.1 port 1179 as 4242420001;
>  neighbor 198.19.0.0 port 1179 as 4242420000;
>};

>protocol static { route 198.18.2.0/24 reject; ipv4 { }; }
>protocol bgp R0 {
>  ipv4 {
>    import all;
>    export filter {
>      # here we export the whole net
>      if source ~ [RTS_STATIC, RTS_BGP] then {
>	bgp_med = 200;
>        accept;
>      }
>      reject;
>    };
>  };
>  local 198.19.0.2 port 1179 as 4242420002;
>  neighbor 198.19.0.0 port 1179 as 4242420000;
>};