(1.1.1.2) noc-core-routerA  <------ fail over 1.1.1.1 -------->   noc-core-routerB (1.1.1.3)
                                __.                         .___ 
                                 /|                         |\
                                /                             \
                               /                               \
  (1.1.2.2) noc-customer-switchA  <-- fail over 1.1.2.1 --->  noc-customer-switchB (1.1.2.3)
                facing                                            facing

noc
----------------------------------------------------------------------------------------------
customer

 (1.1.10.2) managed-l3-switchA <------- fail over 1.1.10.1 ---------> managed-l3-switchB (1.1.10.3)
                          \  \_______________________.                  /      /
                           \           .______________\________________/      /
-----------------------------------------------------------------------------------------------------
                             \        /                 \                   /
                       customer-l2-switch1                customer-l2-switch2
                           /                              (optional)
                          /
                         /
            customer-machine
            1.1.10.49 using 1.1.10.1 as gateway