How to achieve load balancing of router lines?

Problem:I have a Cisco 2811 router with four T1 v2 wan interface cards. Two wan interface cards are used for dedicated lines. The other two wan interface cards are used to connect to the T1 line of the Internet. Currently, only one line is in use. We just bought a T1 line with another IP address from a different Internet service provider. I want these connections to the Internet to achieve load balancing and provide the service transfer function when a line fails. I don't know how to set this configuration. What does my Internet Service Provider need to do? How do I Configure My vro?
Answer:Your Internet service provider does not need to do anything. To achieve load balancing, the first step is to create an access list and divide your network into two parts. Based on the access list, you can define half of the IP addresses on one line and the other half on another line.
Assume that your network is 172.16.128.0/24. "Allow IP address 10.172.16.128.0 0.0.254 access list 1" will only allow Dual IP addresses. Therefore, you now have two subnets. You have to modify the list based on each request and IP address. Now you can create a route chart.
Route map 10 ISP1_primary (Route table 10, first major ISP)
Match access-list 1 (matching access list 1)
Set interface ISP1_interface (Set interface as the first primary ISP interface)
Route map 20 ISP1_primary (Route table 20, first major ISP)
Match access-list 1 (matching access list 1)
Set interface ISP2_interface (Set the interface as the second main ISP interface)
Similarly, you need to create another route table for the second ISP.
Route map 10 ISP2_primary (Route table 10, second main ISP)
Match access-list 2 (matching access list 2)
Set interface ISP2_interface (Set the interface as the second main ISP interface)
Route map 20 ISP1_primary (Route table 20, second main ISP)
Match access-list 2 (matching access list 2)
Set interface ISP1_interface (Set interface as the first primary ISP interface)
Access list 2 is another access list that matches the network. You need to use your own method to divide the network. Another option is to add a floating point static route on the router.