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› › BGP VM with BIRD2, how to route outgoing traffic via the IP in the dummy adapter instead of main IP?
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BGP VM with BIRD2, how to route outgoing traffic via the IP in the dummy adapter instead of main IP?

dnwkdnwk Member
in Help

With below configuration, I could ping the IP and access the IP on the dummy adapter. However, on the server, when I try to run curl ifconfig.co/ I got my main IP. How do I set the dummy to the default route?
Thanks

Here is my BIRD2 configure

define OURASN = ;
define OURIPv6 = ;
define OURIPv4 = ;
define OURIPv6_2 = ;
define MyIPV6Block =;
log syslog all;

router id OURIPv4;

protocol device {
        scan time 5;
}

protocol direct {
        interface "dummy*";
        ipv6;
}

protocol static localmap{
        ipv6;
        route MyIPV6Block via OURIPv6%ens19;
}
protocol kernel {
        ipv6 { import all; };
        learn;
}

protocol bgp s1{
        description "s1";
        local OURIPv6 as OURASN;
        interface "ens18";
        neighbor NEIGHBOURIP1 as NEIGHBOURAS1;
        ipv6 {
                import all;
                export where proto = "localmap";
        };
}

protocol bgp s2{
        description "s2";
        local OURIPv6_2 as OURASN;
        neighbor NEIGHBOURIP2fas NEIGHBOURAS2;
        interface "ens19";
        ipv6 {
                import all;
                export where proto ="localmap";
        };
}

Here is how I add IP to dummy

ip link add dev dummy1 type dummy
ip link set dummy1 up
ip addr add dev dummy1 MYIPV6ADDRESS

Comments

  • cadddrcadddr Member

    you can do that with ip r add default $GW src $DUMMYIP metric 256 , or have bird export the routes to kernel table with krt_prefsrc.

  • dnwkdnwk Member

    @cadddr said:
    you can do that with ip r add default $GW src $DUMMYIP metric 256 , or have bird export the routes to kernel table with krt_prefsrc.

    Could you show me an example of full Kernel config? And for $GW, what is my $GW, I haven't figured out. Is it the same as my VM's public IP?

  • doghouchdoghouch Member
    edited August 2022

    @dnwk said:

    @cadddr said:
    you can do that with ip r add default $GW src $DUMMYIP metric 256 , or have bird export the routes to kernel table with krt_prefsrc.

    Could you show me an example of full Kernel config? And for $GW, what is my $GW, I haven't figured out. Is it the same as my VM's public IP?

    • $GW refers to your gateway. The command above adds a ‘default’ route, which means (in general) that traffic will be routed through there when trying to access resources on the Internet. Think of it like this: you’re on a remote island and you can send requests locally. Any ‘international’ traffic needs to go through an airport (gateway) to reach other networks.
    • The ‘metric’ value is a sort of ‘priority’ number — the lower the metric => the more the route is preferred.
    • The gateway is not the same as your public IP.
  • cadddrcadddr Member
    edited August 2022 
    protocol kernel {
    learn on;

    ipv6 {
        import all;
        export filter {
            if source !~ [RTS_STATIC, RTS_BGP] then reject;

            krt_prefsrc = OURIPV6;
            accept;
        };
    };
}

    This would export all routes(~150k) to the kernel table with the preferred src attribute. Replace OURIPV6 with $DUMMYIP.

    Since you can reach your announced ips without exporting anything i presume the same gateway(that you configured for the vm, check with ip -6 r get ::/0) is used as the nexthop.

  • dnwkdnwk Member

    @cadddr said:

    protocol kernel {
    learn on;

    ipv6 {
        import all;
        export filter {
            if source !~ [RTS_STATIC, RTS_BGP] then reject;

            krt_prefsrc = OURIPV6;
            accept;
        };
    };
}

    This would export all routes(~150k) to the kernel table with the preferred src attribute. Replace OURIPV6 with $DUMMYIP.

    Since you can reach your announced ips without exporting anything i presume the same gateway(that you configured for the vm, check with ip -6 r get ::/0) is used as the nexthop.

    Success! Thanks! With this kernel configure, my outgoing IP is set to the one in my dummy adapter!
    By the way, ip -6 r get ::/0 doesn't work. it says "need at least a destination address"

  • cadddrcadddr Member

    @dnwk said: By the way, ip -6 r get ::/0 doesn't work.

    Try ip -6 r show ::/0.

  • dnwkdnwk Member

    What does bgp_path.prepend AS Path prepending do? Does it make incoming connection to choose the preferred upstream?

  • rubenruben Member, Host Rep

    @dnwk said: What does bgp_path.prepend AS Path prepending do?

    The effect depends on where you put it, on import or export.
    Usually, it's in the export filter. When prepending a prefix on export, the path for a prefix becomes longer for the peer, hence usually less preferred for inbound traffic.

    That said, a peer may have a preference set on their import filter, which overrules the as-path length.

    Thanked by 1dnwk
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