# normal state: all links in
# working condition
traceroute -In 10.4.1.25
 1  10.3.1.21    # primary VPN
                 # router site 3
 2  172.16.0.8   # primary VPN
                 # router site 4
 3  10.4.1.25    # target host
                 # in site 4
# Problem: First link broken
# and network has converged
traceroute -In 10.4.1.25
 1  10.3.1.22    # backup VPN
                 # router site 3
 2  172.16.1.7   # backup VPN
                 # router site 4
 3  10.4.1.25