how can i dynamically change the gateway?

1 Sep 2022


      Hi, I have this script that configures routes for me between different 
routers and servers.
I have a few routers that have down in the wan and connect with the mesh 
network.
How can I dynamically change the gateway?
Example: if the wan drops, use the mesh as the gateway.


# Configure logging
log syslog all;
log "/var/log/bird.log" all;
log stderr all;
router id from "br-lan";

# Sync bird routing table with kernel
protocol kernel kernel4 {
     description "Kernel protocol for IPv4";
     metric 50;
     ipv4 {
         table master4;
         export filter {
             if proto = "lan" then reject;
             accept;
         };
         import all;
     };
};

protocol kernel kernel6 {
     description "Kernel protocol for IPv6";
     metric 300;
     ipv6 {
         table master6;
         export filter {
             if proto = "lan" then reject;
             accept;
         };
         import all;
     };
};

protocol device {
     description "Device protocol";
};

protocol direct lan {
     description "LAN protocol";
     ipv4;
     ipv6;
     interface "br-lan";
     check link;
}
protocol babel ninux {
     description "Babel protocol for NINUX network";
     ipv4 {
         export where (source = RTS_DEVICE) || (source = RTS_BABEL);
     };
     ipv6 {
         export where (source = RTS_DEVICE) || (source = RTS_BABEL);
     };
     interface "vpnbas" {
         check link;
     };
## Used to connect with other neighbours on the same layer 2 network.
## Decomment the config to use it, not this comments of course!
## Use the correct name interface, not the logical openwrt/(l)uci one.
## You can define more interfaces maches using * in regex (like "ifnet*")
## or "ifnet1", "ifnet2", "ifnetN", "otherifnetnames" form.
## You can also define more interfaces with other parameters, please refer to:
##https://bird.network.cz/?get_doc&v=20&f=bird-6.html#ss6.1
## After, reload the bird daemon with: /etc/init.d/bird reload
## or if you perefer, reastart with: /etc/init.d/bird restart
     interface "mesh" {
         type wireless; # or wired
         check link;
     };
}

how can i dynamically change the gateway?

Michele Salerno