A Multiprotocol Label Switching(MPLS) Layer 3 Virtual Private Network (VPN) consists of a set of sites that are interconnected by means of an MPLS provider core network. At each customer site, one or more customer edge (CE) routers attach to one or more provider edge (PE) routers.
Reference:
https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k-r6-5/lxvpn/configuration/g uide/b-l3vpn-cg-asr9000-65x/b-l3vpn-cg-asr9000-65x_chapter_010.pdf

https://networklessons.com/cisco/ccna-routing-switching-icnd1-100-105/floating-static-route If we want to use a static route as a backup route, we'll have to change its administrative distance. This is called a floating static route.
https://www.geeksforgeeks.org/what-is-floating-static-route/
higher admin value to make a secondary route:
Router(config)#ip route 192.168.60.0 255.255.255.0 192.168.40.2 (primary route) Router(config)#ip route 192.168.60.0 255.255.255.0 192.168.20.2 10 (secondary route)

With this configuration, when Track 1 is UP, traffic to the Internet (8.8.8.8 is the well-known DNS of Google) flows through ISP1. When Track 1 is DOWN, traffic to the Internet flows through ISP
2. But there is a problem with this configuration is we did not specify the source IP of the track.
Usually, our router (R1 in the figure below) is connected to two ISPs via two different interface like this:

So if we don't specify the source IP, R1 will ping via E0/0 to ISP1. If the ping fails, R1 will remove the first default route so the backup path via ISP2 will be used and traffic will be sent via E0/1. But it also makes the track UP again (as we did not specify the source IP) and the main path is installed again to the routing table -> The connection will flap between two ISPs.
Therefore, in order to solve this issue, we must configure a source IP for the ping. In the example above, we can configure like this: "icmp-echo 8.8.8.8 source-ip 10.0.12.1".
Note: The configuration above means:
Timeout: 2000 milliseconds
frequency: 5 seconds
threshold: 1000 milliseconds
Reference: https://www.cisco.com/c/en/us/support/docs/ip/ip-routing/200785-ISP-Failover-with- default-routes-using-I.html

MPLS uses a 32-bit label field that contains the information that follows:
+ 20-bit label (a number)
+ 3-bit class of service (or experimental field, typically used to carry IP precedence value)
+ 1-bit bottom-of-stack indicator (indicates whether this is the last label before the IP header)
+ 8-bit TTL (equal to the TTL in the IP header)