The backup connection between the two branches

A tunnel is organized between the two branches via the ISP. For redundancy, a second tunnel is organized over the network of another ISP.

Scheme with IP-addresses:

Switching to the backup route is performed when OSPF connectivity is lost through the tunnel over the network of the ISP “A”. BFD is used to quickly evaluate connectivity.

The settings for routers:

Router WEST

hostname WEST
no ip domain lookup

interface Loopback0
 no shutdown
 description PC_A
 ip address 172.16.1.1 255.255.255.0

interface Tunnel0
 no shutdown
 ip address 172.16.12.1 255.255.255.252
 bfd interval 50 min_rx 50 multiplier 3
 tunnel source 10.1.1.1
 tunnel destination 10.2.2.1

interface Tunnel1
 no shutdown
 description RESERV
 ip address 172.16.21.1 255.255.255.252
 ip ospf cost 1500
 bfd interval 50 min_rx 50 multiplier 3
 tunnel source 10.3.3.1
 tunnel destination 10.4.4.1

interface GigabitEthernet0/0
 no shutdown
 description to_ISP_A
 ip address 10.1.1.1 255.255.255.252
 duplex auto
 speed auto
 media-type rj45

interface GigabitEthernet0/1
 no shutdown
 description to_ISP_B
 ip address 10.3.3.1 255.255.255.252
 duplex auto
 speed auto
 media-type rj45

router ospf 1
 log-adjacency-changes detail
 network 172.16.1.0 0.0.0.255 area 0
 network 172.16.12.0 0.0.0.3 area 0
 network 172.16.21.0 0.0.0.3 area 0
 bfd all-interfaces

ip route 10.2.2.0 255.255.255.252 10.1.1.2
ip route 10.4.4.0 255.255.255.252 10.3.3.2

line con 0
 exec-timeout 0 0
 logging synchronous

Router EAST

hostname EAST
no ip domain lookup

interface Loopback0
 no shutdown
 description PC_B
 ip address 172.16.2.1 255.255.255.0

interface Tunnel0
 no shutdown
 ip address 172.16.12.2 255.255.255.252
 bfd interval 50 min_rx 50 multiplier 3
 tunnel source 10.2.2.1
 tunnel destination 10.1.1.1

interface Tunnel1
 no shutdown
 description RESERV
 ip address 172.16.21.2 255.255.255.252
 ip ospf cost 1500
 bfd interval 50 min_rx 50 multiplier 3
 tunnel source 10.4.4.1
 tunnel destination 10.3.3.1

interface GigabitEthernet0/0
 no shutdown
 description to_ISP_A
 ip address 10.2.2.1 255.255.255.252
 duplex auto
 speed auto
 media-type rj45

interface GigabitEthernet0/1
 no shutdown
 description to_ISP_B
 ip address 10.4.4.1 255.255.255.252
 duplex auto
 speed auto
 media-type rj45

router ospf 1
 log-adjacency-changes detail
 network 172.16.2.0 0.0.0.255 area 0
 network 172.16.12.0 0.0.0.3 area 0
 network 172.16.21.0 0.0.0.3 area 0
 bfd all-interfaces

ip route 10.1.1.0 255.255.255.252 10.2.2.2
ip route 10.3.3.0 255.255.255.252 10.4.4.2

line con 0
 exec-timeout 0 0
 logging synchronous

Router ISP_A

hostname ISP_A
no ip domain lookup

interface GigabitEthernet0/0
 no shutdown
 description to_WEST
 ip address 10.1.1.2 255.255.255.252
 duplex auto
 speed auto
 media-type rj45

interface GigabitEthernet0/1
 no shutdown
 description to_EAST
 ip address 10.2.2.2 255.255.255.252
 duplex auto
 speed auto
 media-type rj45

line con 0
 exec-timeout 0 0
 logging synchronous

Router ISP_B

hostname ISP_B
no ip domain lookup

interface GigabitEthernet0/0
 no shutdown
 description to_WEST
 ip address 10.3.3.2 255.255.255.252
 duplex auto
 speed auto
 media-type rj45

interface GigabitEthernet0/1
 no shutdown
 description to_EAST
 ip address 10.4.4.2 255.255.255.252
 duplex auto
 speed auto
 media-type rj45

line con 0
 exec-timeout 0 0
 logging synchronous