Hi Liu,
are you talking about the channel option `gateway recursive`
(https://bird.nic.cz/doc/bird-2.18.html#bgp-gateway) and that even with
it on it still does not work?
If I understand your issue correctly, this should resolve the issue you
are having (keep in mind that the option in not compatible with sorted
tables).
In BIRD v3 you should be able to see item host-entry in the route info
(via `show route table all all` or similar), unfortunately this
information is not present in v2.
You are right that BIRD should do this better right away. However to fix
this, a much bigger refactor of the code is required.
It is on our backlog, but we can not promise you that the changes will
made in time for the release of v2.19.
Hope this helps a bit,
David
David Petera (he/him) | BIRD Tech Support | CZ.NIC, z.s.p.o.
On 1/11/26 22:40, Pysio wrote:
Hi Alexander,
Thanks for the tips!
I just tried the multihop (recursive) approach, but unfortunately, it
didn't change anything. Even with multihop on, BIRD still picks ens23
for the next hop resolution. It seems like it's still looking at the
global interface list instead of sticking to the route in the specific
table I've assigned.
I'll give VRFs a shot later tonight to see if that fixes
While VRFs should work as a workaround, I still feel like BIRD should
ideally handle this better out of the box. In a multi-table setup,
you'd expect it to prioritize the lookup within the attached table first.
Anyway, I’ll let you know how the VRF test goes!
Best,
Liu HaoRan
On Mon, Jan 12, 2026 at 3:03 AM Alexander Zubkov <[email protected]> wrote:
I probably saw something like that bug for IPv6, so not sure if it
is the same. And I did not have separate tables for the
interfaces. But worth a check anyway. It seemed to me that direct
sessions created routes with the interface and ip through that the
bgi session was installed. And recursive (multihop) sessions set
the routes to the first found interface (I remind, I had all them
in one table).
So you can try to change protocol to recursive to check (but it
could have other drawbacks) if it would use the appropriate route
from the attached table.
Also, if you wander of the possible solutions, I think you could
play with vrfs to divide the interfaces routing, bird is aware of
vrfs.
On Sun, Jan 11, 2026 at 7:09 PM Pysio <[email protected]> wrote:
Additionally, I should mention that the issue persists even
when I explicitly declare the IGP table using the following
configuration file.
protocol bgp cloudflare_tpix_210440_v4 {
local as 210440;
source address 203.163.223.48;
neighbor 203.163.222.39 as 13335;
ipv4 {
table table_tpix_210440_v4;
import keep filtered on;
import where import_filter_v4();
export where export_filter_tpix_210440();
graceful restart on;
export limit 99 action block;
igp table table_tpix_210440_v4;
};
}
BIRD 2.17.1 ready.
Table table_tpix_210440_v4:
1.1.1.0/24 <http://1.1.1.0/24> unicast
[cloudflare_tpix_210440_v4 2026-01-12 02:07:03] * (100) [AS13335i]
via 203.163.222.39 on ens23
Type: BGP univ
BGP.origin: IGP
BGP.as_path: 13335
BGP.next_hop: 203.163.222.39
BGP.local_pref: 100
BGP.aggregator: 162.158.240.1 AS13335
BGP.community: (13335,10080)
BGP.large_community: (213605, 10, 1) (213605, 10, 4)
BIRD 2.17.1 ready.
Table table_tpix_210440_v4:
203.163.222.0/23 <http://203.163.222.0/23> unicast
[direct_tpix_210440 2026-01-12 02:04:33] * (240)
dev ens4
Type: device univ
On Mon, Jan 12, 2026 at 1:57 AM Pysio
<[email protected]> wrote:
Hi Alexander,
Thank you for your response. To answer your question: yes,
I am using specific tables (e.g., |table_tpix_210440_v4|)
for each BGP session, and I have corresponding |protocol
direct| instances to populate those tables with the
respective interface routes.
However, despite having a valid direct route in the
specific table, BIRD still resolves the BGP next hop via
|ens23| (the first interface in the kernel's subnet list)
instead of honoring the device route defined in the local
table.
Below is the relevant part of my configuration for your
review.
```config|
table table_tpix_210440_v4;
table table_tpix_210440_v6;
protocol direct direct_tpix_210440 {
ipv4 { table table_tpix_210440_v4; };
ipv6 { table table_tpix_210440_v6; };
interface "ens4";
}
protocol bgp cloudflare_tpix_210440_v4 {
local as 210440;
source address 203.163.223.48;
neighbor 203.163.222.39 as 13335;
ipv4 {
table table_tpix_210440_v4;
import keep filtered on;
import where import_filter_v4();
export where export_filter_tpix_210440();
graceful restart on;
export limit 99 action block;
};
}
|
```
Even though |table_tpix_210440_v4| contains a direct route
for |203.163.222.0/23 <http://203.163.222.0/23>| via
|ens4|, BIRD's |show route| output for the BGP session on
|ens4| indicates the next hop is resolved via |ens23|.
On Mon, Jan 12, 2026 at 1:06 AM Alexander Zubkov
<[email protected]> wrote:
Hi Lui,
Does cloudflare_tpix_210440_v4 bgp protocol
use table_tpix_210440_v4 as IGP table also? It might
be better to have an overview of your config file.
Regards,
Alexander
On Sun, Jan 11, 2026 at 3:14 PM HaoRanLiu
<[email protected]> wrote:
Hello,
I am writing to report a potential issue (or seek
clarification on
resolution logic) in BIRD 2.17.1 regarding how
next hops are resolved
when multiple interfaces exist in the same subnet.
[ Environment ]
- BIRD version: 2.17.1
- OS: Linux
- Setup: Multiple physical interfaces (ens4,
ens23, ens2) are configured
with IP addresses in the same prefix:
203.163.222.0/23 <http://203.163.222.0/23>.
[ Observation ]
Within a specific routing table
(table_tpix_210440_v4), BIRD's recursive
resolution for a BGP route does not seem to honor
the "Direct/Device"
route present in that same table.
[ Evidence ]
1. The Direct Route in table
"table_tpix_210440_v4" points to ens4:
bird> show route for 203.163.222.39/32
<http://203.163.222.39/32> table
table_tpix_210440_v4 all
Table table_tpix_210440_v4:
203.163.222.0/23 <http://203.163.222.0/23>
unicast [direct_tpix_210440 2026-01-11 21:10:29] *
(240)
dev ens4
Type: device univ
2. However, a BGP route in the SAME table resolves
via ens23:
bird> show route for 1.1.1.1 table
table_tpix_210440_v4 all
Table table_tpix_210440_v4:
1.1.1.0/24 <http://1.1.1.0/24> unicast
[cloudflare_tpix_210440_v4 2026-01-11
21:33:43] * (100) [AS13335i]
via 203.163.222.39 on ens23
Type: BGP univ
BGP.origin: IGP
BGP.as_path: 13335
BGP.next_hop: 203.163.222.39
...
[ System Network State ]
The OS kernel shows three interfaces in this subnet:
# ip route show 203.163.222.0/23
<http://203.163.222.0/23>
203.163.222.0/23 <http://203.163.222.0/23> dev
ens23 proto kernel scope link src 203.163.223.49
203.163.222.0/23 <http://203.163.222.0/23> dev
ens2 proto kernel scope link src 203.163.223.50
203.163.222.0/23 <http://203.163.222.0/23> dev
ens4 proto kernel scope link src 203.163.223.48
[ Questions ]
1. Is this a bug in the recursive resolution
logic? It appears BIRD
might be picking an interface from the global
interface list (perhaps
the first one UP) rather than following the best
route available in the
specific table being queried.
2. Why does the BGP route's "via" field not honor
the interface (ens4)
defined by the device route in the same table?
3. Is there any configuration to force BIRD to
resolve next hops
strictly based on the current table's best path in
such multi-homed
scenarios?
Any insights would be appreciated.
Best regards,
Liu HaoRan
