Here’s an example to demonstrate this in more detail.
If the San Jose router in this topology is advertising network 10.0.0.0/8
to the San Francisco router using RIP version 2
the San Francisco router will deem that the believability factor
or administrative distance of that route is 120.
If the same network was advertised by the New York router using EIGRP
the San Francisco router will allocate that route
a believability or admin distance of 90.
the San Francisco router will does install this route received
via EIGRP from the New York router into its local routing table
and traffic received going to an IP address of 10.1.1.1 for example
will be routed to the New York router and not to the San Jose router.
The same network is received from the different neighboring devices
via different routing protocols
and administrative distance was used in this example as a tie breaker.
The more believable routing protocol is EIGRP
the RIP route is not installed
in the local routing table on the San Francisco router.
The EIGRP route is installed and traffic is routed
to New York to get to host in this network.
now the San Francisco router still has the RIP route
in its RIP database so if the EIGRP route was no longer available
the RIP route will be installed in the routing table
and San Francisco would route the traffic to San Jose
to get to host devices in network 10.0.0.0
in other words, if this link went down for some reason
and there was no connectivity between San Francisco
and New York traffic will then be sent to San Jose
but if the link came back again the EIGRP route
that’s then advertised would supersede the RIP route
and traffic will now be routed to New York.
So New York is the first choice
and will be used if that neighbor is available
and San Jose is the 2nd choice to get to the same network.