<div dir="ltr">Hi Alexander,<br><br>Thanks for the tips!<br><br>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.<br><br>I'll give VRFs a shot later tonight to see if that fixes<br><br>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.<br><br>Anyway, I’ll let you know how the VRF test goes!<br><br>Best,<br><br>Liu HaoRan</div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Mon, Jan 12, 2026 at 3:03 AM Alexander Zubkov <<a href="mailto:green@qrator.net">green@qrator.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>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).</div><div>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.</div><div>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.</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Jan 11, 2026 at 7:09 PM Pysio <<a href="mailto:mcyouyousever@gmail.com" target="_blank">mcyouyousever@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Additionally, I should mention that the issue persists even when I explicitly declare the IGP table using the following configuration file.<div><br></div><div>protocol bgp cloudflare_tpix_210440_v4 {<br> local as 210440;<br> source address 203.163.223.48;<br> neighbor 203.163.222.39 as 13335;<br> ipv4 {<br> table table_tpix_210440_v4;<br> import keep filtered on;<br> import where import_filter_v4();<br> export where export_filter_tpix_210440();<br> graceful restart on;<br> export limit 99 action block;<br> igp table table_tpix_210440_v4;<br> };<br>}</div><div><br></div><div>BIRD 2.17.1 ready.<br>Table table_tpix_210440_v4:<br><a href="http://1.1.1.0/24" target="_blank">1.1.1.0/24</a> unicast [cloudflare_tpix_210440_v4 2026-01-12 02:07:03] * (100) [AS13335i]<br> via 203.163.222.39 on ens23<br> Type: BGP univ<br> BGP.origin: IGP<br> BGP.as_path: 13335<br> BGP.next_hop: 203.163.222.39<br> BGP.local_pref: 100<br> BGP.aggregator: 162.158.240.1 AS13335<br> BGP.community: (13335,10080)<br> BGP.large_community: (213605, 10, 1) (213605, 10, 4)<br><br><br></div><div>BIRD 2.17.1 ready.<br>Table table_tpix_210440_v4:<br><a href="http://203.163.222.0/23" target="_blank">203.163.222.0/23</a> unicast [direct_tpix_210440 2026-01-12 02:04:33] * (240)<br> dev ens4<br> Type: device univ</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Jan 12, 2026 at 1:57 AM Pysio <<a href="mailto:mcyouyousever@gmail.com" target="_blank">mcyouyousever@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><p>Hi Alexander,</p>
<p>Thank you for your response. To answer your question: yes, I am using specific tables (e.g., <code>table_tpix_210440_v4</code>) for each BGP session, and I have corresponding <code>protocol direct</code> instances to populate those tables with the respective interface routes.</p>
<p>However, despite having a valid direct route in the specific table, BIRD still resolves the BGP next hop via <code>ens23</code> (the first interface in the kernel's subnet list) instead of honoring the device route defined in the local table.</p>
<p>Below is the relevant part of my configuration for your review.</p>
<p>```config<code><br>
table table_tpix_210440_v4;<br>
table table_tpix_210440_v6;<br>
<br>
protocol direct direct_tpix_210440 {<br>
ipv4 { table table_tpix_210440_v4; };<br>
ipv6 { table table_tpix_210440_v6; };<br>
interface "ens4";<br>
}<br>
<br>
<br>
protocol bgp cloudflare_tpix_210440_v4 {<br>
local as 210440;<br>
source address 203.163.223.48;<br>
neighbor 203.163.222.39 as 13335;<br>
ipv4 {<br>
table table_tpix_210440_v4;<br>
import keep filtered on;<br>
import where import_filter_v4();<br>
export where export_filter_tpix_210440();<br>
graceful restart on;<br>
export limit 99 action block;<br>
};<br>
}<br>
</code><br>
</p>
<p>```</p>
<p>Even though <code>table_tpix_210440_v4</code> contains a direct route for <code><a href="http://203.163.222.0/23" target="_blank">203.163.222.0/23</a></code> via <code>ens4</code>, BIRD's <code>show route</code> output for the BGP session on <code>ens4</code> indicates the next hop is resolved via <code>ens23</code>.</p></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Jan 12, 2026 at 1:06 AM Alexander Zubkov <<a href="mailto:green@qrator.net" target="_blank">green@qrator.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>Hi Lui,</div><div><br></div><div>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.</div><div><br></div><div>Regards,</div><div>Alexander</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Jan 11, 2026 at 3:14 PM HaoRanLiu <<a href="mailto:mcyouyousever@gmail.com" target="_blank">mcyouyousever@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hello,<br>
<br>
I am writing to report a potential issue (or seek clarification on <br>
resolution logic) in BIRD 2.17.1 regarding how next hops are resolved <br>
when multiple interfaces exist in the same subnet.<br>
<br>
[ Environment ]<br>
- BIRD version: 2.17.1<br>
- OS: Linux<br>
- Setup: Multiple physical interfaces (ens4, ens23, ens2) are configured <br>
with IP addresses in the same prefix: <a href="http://203.163.222.0/23" rel="noreferrer" target="_blank">203.163.222.0/23</a>.<br>
<br>
[ Observation ]<br>
Within a specific routing table (table_tpix_210440_v4), BIRD's recursive <br>
resolution for a BGP route does not seem to honor the "Direct/Device" <br>
route present in that same table.<br>
<br>
[ Evidence ]<br>
<br>
1. The Direct Route in table "table_tpix_210440_v4" points to ens4:<br>
<br>
bird> show route for <a href="http://203.163.222.39/32" rel="noreferrer" target="_blank">203.163.222.39/32</a> table table_tpix_210440_v4 all<br>
Table table_tpix_210440_v4:<br>
<a href="http://203.163.222.0/23" rel="noreferrer" target="_blank">203.163.222.0/23</a> unicast [direct_tpix_210440 2026-01-11 21:10:29] * <br>
(240)<br>
dev ens4<br>
Type: device univ<br>
<br>
2. However, a BGP route in the SAME table resolves via ens23:<br>
<br>
bird> show route for 1.1.1.1 table table_tpix_210440_v4 all<br>
Table table_tpix_210440_v4:<br>
<a href="http://1.1.1.0/24" rel="noreferrer" target="_blank">1.1.1.0/24</a> unicast [cloudflare_tpix_210440_v4 2026-01-11 <br>
21:33:43] * (100) [AS13335i]<br>
via 203.163.222.39 on ens23<br>
Type: BGP univ<br>
BGP.origin: IGP<br>
BGP.as_path: 13335<br>
BGP.next_hop: 203.163.222.39<br>
...<br>
<br>
[ System Network State ]<br>
The OS kernel shows three interfaces in this subnet:<br>
<br>
# ip route show <a href="http://203.163.222.0/23" rel="noreferrer" target="_blank">203.163.222.0/23</a><br>
<a href="http://203.163.222.0/23" rel="noreferrer" target="_blank">203.163.222.0/23</a> dev ens23 proto kernel scope link src 203.163.223.49<br>
<a href="http://203.163.222.0/23" rel="noreferrer" target="_blank">203.163.222.0/23</a> dev ens2 proto kernel scope link src 203.163.223.50<br>
<a href="http://203.163.222.0/23" rel="noreferrer" target="_blank">203.163.222.0/23</a> dev ens4 proto kernel scope link src 203.163.223.48<br>
<br>
[ Questions ]<br>
1. Is this a bug in the recursive resolution logic? It appears BIRD <br>
might be picking an interface from the global interface list (perhaps <br>
the first one UP) rather than following the best route available in the <br>
specific table being queried.<br>
2. Why does the BGP route's "via" field not honor the interface (ens4) <br>
defined by the device route in the same table?<br>
3. Is there any configuration to force BIRD to resolve next hops <br>
strictly based on the current table's best path in such multi-homed <br>
scenarios?<br>
<br>
Any insights would be appreciated.<br>
<br>
Best regards,<br>
Liu HaoRan<br>
<br>
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