Dear Mates,
I Found that Default routing got Highest priority when the bonding exist.
When a link which is become slave of bonding interface goes down, the bonding interface become unstable due to other routing which is used to form the tunnel has lower priority, and since it has lower priority all destination address including that is used for tunnels has to go via default gateway.

The Story
I create bonding over two eoip tunnel interface, each eoip tunnel interface connected through different telco vendor. In order to get redundancy and fail over.

Topology as seen on attachment

IP Address for Bonding
ip address Bonding A: 10.1.1.2/30
ip address Bonding B: 10.1.1.1/30

Routing table for router A
ip route dst-address=0.0.0.0/0 gateway=10.1.1.1
ip route dst-address=172.1.1.0/30 gateway=10.1.1.2 ( this is to forward via Telco A)
ip route dst-address=180.1.1.0/30 gateway=20.1.1.2 ( this is to forward via Telco B)


To solve this problem, i create route marking with mangle from LAN subnet on Router A.
Then I create the default routing (0.0.0.0/0) with route-marking that i made before.

When a link disconnected the bonding connection is stable and failover working seamlessly.

Anybody Please advise why the default routing become superior and has highest priority than other.
Without Bonding interface, the default routing will not become superior. Always become the lowest priority.

This is happened from ROS 3.xx until 4.5

Thanks in advance..!!
cheers

Julius