I am trying to configure WAN redundancy across a pair of links, using ip sla to monitor link state and switch routes if one fails.
The design uses Loopback0 as a NAT interface, with the two WAN interfaces as transit networks. The ISP routers will have dynamic routing such that the IP assigned to Loopback0 will be accessible over either link.
The config currently looks like so:
track 100 ip sla 1 reachability
!
interface Loopback0
ip address 1.2.3.224 255.255.255.254
ip nat outside
ip virtual-reassembly in
!
interface GigabitEthernet0/0
description COLT WAN
ip address 1.2.3.9 255.255.255.254
ip virtual-reassembly in
duplex full
speed 100
no cdp enable
!
interface GigabitEthernet0/1
description INSIDE LAN
ip address 172.200.0.1 255.255.0.0
ip nat inside
ip virtual-reassembly in
duplex full
speed 100
!
interface GigabitEthernet0/1/0
description VODAFONE INTERCONNECT
switchport access vlan 100
no ip address
duplex full
speed 100
no cdp enable
!
interface Vlan100
description VODAFONE WAN
ip address 1.2.3.135 255.255.255.254
ip virtual-reassembly in
!
ip route 0.0.0.0 0.0.0.0 1.2.3.134 track 100
ip route 0.0.0.0 0.0.0.0 1.2.3.8 200
!
ip sla 1
icmp-echo 1.2.3.134 source-ip 1.2.3.135
frequency 5000
ip sla schedule 1 life forever start-time now
The router can ping 1.2.3.8
and 1.2.3.134
, and both of these can ping 1.2.3.224
. I have also verified that the redundant routing works if one of the links are down, although this doesn't appear to have any relation to this NAT issue.
From 172.200.0.0/24
I am able to ping 172.200.0.1
, 1.2.3.224
, 1.2.3.9
and 1.2.3.135
but not 1.2.3.8
or 1.2.3.134