How to advertise two virtual IPs using BGP?

20 Nov 2024

      Hi all!

I have a dual-home server, whose connection topology and configuration is described as below.

**** Connection Topology and Configuration ****

The server has two physical NICs enp4s0f0 and enp4s0f1, which are connected to two separate ports TOR_A and TOR_B on a Top of Rack (TOR) router, each representing a separate BGP session through bgp_A and bgp_B protocol.

The server also has a dummy interface named em5, which has a private ip 38.145.72.193/32.

Bird kernel protocol exports an ECMP routing rule to kernel as a kernel default routing, and bgp_A/bgp_B protocol export the private ip to my internet, then 38.145.72.193/32 on em5 acts as a public ip.

****   My goal ****

I want to add another virtual ip on em5, say 38.145.72.198/32, and let this new virtual ip act as a public ip too.
Can this requirement be met? If yes, how should I modify the configuration to make BGP advertise this ip over my internet?

**** Additional Information on Server ****

## bird setup an ECMP route on 2 phy nics as default route,
## which set source ip to the public ip
$ ip route
default proto bird src 38.145.72.193 metric 32
        nexthop via 10.105.1.10 dev enp4s0f0 weight 1
        nexthop via 10.105.1.12 dev enp4s0f1 weight 1
10.105.1.10/31 dev enp4s0f0 proto kernel scope link src 10.105.1.11
10.105.1.12/31 dev enp4s0f1 proto kernel scope link src 10.105.1.13

bird> show route all
Table master4:
0.0.0.0/0            unicast [bgp_A 2024-11-17] * (100) [AS4212010101i]
        via 10.105.1.10 on enp5s0f0
        Type: BGP univ
        BGP.origin: IGP
        BGP.as_path: 4259105001 4212010101
        BGP.next_hop: 10.105.1.10
        BGP.local_pref: 0
                     unicast [bgp_B 2024-11-18] (100) [AS4212010101i]
        via 10.105.1.12 on enp5s0f1
        Type: BGP univ
        BGP.origin: IGP
        BGP.as_path: 4259205001 4212010101
        BGP.next_hop: 10.105.1.12
        BGP.local_pref: 0
38.145.72.193/32     unicast [direct1 2024-11-06] * (240)
        dev em5
        Type: device univ

# bird.conf
router id 172.18.xxx.yyy;
ipv4 table master4;

define LOCAL_NET = [ 38.145.72.193/32 ];

protocol direct {
    ipv4;
    interface em5,-*; 
}

protocol kernel {
    scan time 1;
    merge paths yes limit 4;
    ipv4 {
      import none;
      export filter {
        if proto = direct1 then reject;
        krt_prefsrc = 38.145.72.193;
        accept;
      };
  };
}

protocol device {
    scan time 1;
}

protocol bgp bgp_A {
    description TOR A;
    local 10.105.1.11 as 4290105101 ; # enp4s0f0
    neighbor 10.105.1.10 as 4259105001; # TOR_A
    path metric 1;
    ipv4 {
       import all;
       export filter {
           if net ~ LOCAL_NET then accept;
           else reject;
       };
       next hop self;
     };
}

protocol bgp bgp_B {
    bfd;
    description TOR B;
    local 10.105.1.13 as 4290105101 ; # enp4s0f1
    neighbor 10.105.1.12 as 4259205001; # TOR_B
    default bgp_med 0;
    default bgp_local_pref 0;
    path metric 1;
    ipv4 {
       import all;
       export filter {
           if net ~ LOCAL_NET then accept;
           else reject;
       };
       next hop self;       
     };
}

How to advertise two virtual IPs using BGP?

Hans Heng