How to forward packet using ubuntu route ?

I need to forward packets to some target hosts by target ip, if the target host is down, the packet is passed to one default host.

The target ip has no rule, so i think i need to create many routes. and these routes(about 10 000 items) will be modified frequently.

Is there any better method to deal with this case ?

From serverfault why

• The most common approach for something like this is to either using a routing protocol or a virtual IP. Routing protocols such as BGP or OSPF can take down routes that are no longer working as they use keep alive messages. A Virtual IP is when one server has a secondary IP address, if this server fails the other server will pick up the virtual IP address. You could use ucarp or heartbeat for this.

  The VIP approach is generally simpler depending on what you are trying to do.

  why : I want to know. how to setup BSG ? I need to setup BSG at both target host and gateway host ? Do you have some experiences at BSG ?
  From Kyle Brandt