GRE Backup

Using the following topology:

 

R1:

interface Tunnel12  backup delay 3 3  backup interface Tunnel13  ip address 10.1.12.1 255.255.255.0  keepalive 5 3  tunnel source FastEthernet1/0  tunnel destination 10.1.123.2 ! interface Tunnel13  ip address 10.1.13.1 255.255.255.0  tunnel source FastEthernet1/0  tunnel destination 10.1.123.3 ! interface FastEthernet0/0  no ip address  shutdown  duplex full ! interface FastEthernet1/0  ip address 10.1.123.1 255.255.255.0  speed auto  duplex auto ! ip route 192.168.41.0 255.255.255.0 Tunnel12 ip route 192.168.41.0 255.255.255.0 Tunnel13 50

R2:

interface Tunnel12  ip address 10.1.12.2 255.255.255.0  keepalive 5 3  tunnel source FastEthernet1/0  tunnel destination 10.1.123.1 ! interface FastEthernet1/0  ip address 10.1.123.2 255.255.255.0  speed auto  duplex auto ! interface FastEthernet1/1  ip address 10.1.234.2 255.255.255.0  standby 1 ip 10.1.234.254  standby 1 priority 150  standby 1 preempt  standby 1 track 1 decrement 100  speed auto  duplex auto ! ip route 192.168.41.0 255.255.255.0 10.1.234.4

R3:

interface Tunnel13  ip address 10.1.13.3 255.255.255.0  tunnel source FastEthernet1/0  tunnel destination 10.1.123.1 ! interface FastEthernet1/0  ip address 10.1.123.3 255.255.255.0  speed auto  duplex auto ! interface FastEthernet1/1  ip address 10.1.234.3 255.255.255.0  standby 1 ip 10.1.234.254  standby 1 priority 110  standby 1 preempt  speed auto  duplex auto ! ip route 192.168.41.0 255.255.255.0 10.1.234.4

R4:

interface Loopback1  ip address 192.168.41.1 255.255.255.0 ! interface FastEthernet1/0  ip address 10.1.234.4 255.255.255.0  speed auto  duplex auto ip route 0.0.0.0 0.0.0.0 10.1.234.254

R1 is configured with backup interface - tunnel 13 backup tunnel 12:

R1# show backup Primary Interface          Secondary Interface        Status -------------------------  -------------------------  ------ Tunnel12                   Tunnel13                   normal operation

When tunnel 12 goes down (I used keepalive but we can use other methods like IP-SLA) tunnel 13 become the backup and the floating route starts working:

R1# *Sep 27 11:32:57.495: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel12, changed state to down R1# *Sep 27 11:33:02.503: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel13, changed state to up R1# *Sep 27 11:33:02.523: %LINK-3-UPDOWN: Interface Tunnel13, changed state to up R1#show back R1#show backup Primary Interface          Secondary Interface        Status -------------------------  -------------------------  ------ Tunnel12                   Tunnel13                   backup mode

Note that tunnel 13 is down as long tunnel 12 is up.