RE: bird BGP not advertise local routing, unless make it blackhole

4 Jun 2024

      Classified as: Hitachi Rail – Public

Hi Soha,

Got it. Many thanks for your explanation in detail.

With Best Regards,
Chris

Hitachi Rail – Public
From: Soha Jin <soha@jin.sh>
Sent: Tuesday, June 4, 2024 12:22 PM
To: LIU Chris <chris-zq.liu@urbanandmainlines.com>
Cc: 'BIRD Users' <bird-users@network.cz>
Subject: RE: bird BGP not advertise local routing, unless make it blackhole

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Hello Chris,

According to the documentation, https://bird.network.cz/?get_doc&v=20&f=bird-6.html#ss6.17

A route requires at least one next hop. “route 192.168.0.0/16;” should not pass the configuration check.

Valid routes can be:
route 192.168.0.0/16 blackhole; # drop packets to the destination
route 192.168.0.0/16 reject; # reject packets to the destination
route 192.168.0.0/16 via eth0;
route 192.168.0.0/16 via 192.168.1.1; # 192.168.1.1 is directly reachable
route 192.168.0.0/16 recursive 192.168.1.1; # use next hop by resolving the route to 192.168.1.1

When you announcing the prefix to your neighbor, the neighbor finds next hop with bgp_next_hop, it only knows that 192.168.0.0/16 is reachable via your router, and doesn’t know that prefix is blackholed on your router.

Static routes are the reachability information defined statically on your router, which should be told to the kernel to be effective. If you are not exporting the routes to your kernel (this is actually what you did in the configuration you provided), the blackhole here will not affect your IP packet forwarding.

Regards,
Soha

From: Bird-users <bird-users-bounces@network.cz<mailto:bird-users-bounces@network.cz>> On Behalf Of LIU Chris via Bird-users
Sent: Tuesday, June 4, 2024 11:24 PM
To: BIRD Users <bird-users@network.cz<mailto:bird-users@network.cz>>
Subject: bird BGP not advertise local routing, unless make it blackhole

Classified as: Hitachi Rail – Public

I am new for bird/BGP. My configuration as below. Basically it is working as expected except one thing.
This static routing, I want to advertise this route to BGP peers.
If I just configured as :  route 192.168.0.0/16,  Bird doesn’t advertise this route unless add it as blackhole
blackhole is sink or just drop, why ?

protocol static static_bgp {
    ipv4;
    check link;
    route 192.168.0.0/16 blackhole;
}

------------------------------------------
router id 1.1.1.1;

filter Filter_Export_Kernel {
    if net ~ [ 10.1.0.0/16 ] then {
        accept;
    }
    else
        reject;
}

protocol kernel {
    scan time 10;
    ipv4 {
        export filter Filter_Export_Kernel;
    };
}

protocol device {
    scan time 10;
}

protocol static static_bgp {
    ipv4;
    check link;
    route 192.168.0.0/16 blackhole;
}

protocol bgp BGP_INSTANCE_1 {
    local xx.xx.xx.xx as 10001;
    neighbor yy.yy.yy.yy as 10002;
    ipv4 {
        import all;
        export where proto ="static_bgp";
        preference 200;
    };
    hold time 3;
    bfd on;
}

protocol bfd BFD_INSTANCE_1 {
    interface "eth1" {
        min rx interval 1 s;
        min tx interval 1 s;
        idle tx interval 3000 ms;
        multiplier 3;
    };
    neighbor yy.yy.yy.yy local xx.xx.xx.xx;
}

---------------------------------

Hitachi Rail – Public