LAB: OSPF Reliable Conditional default routing using IP SLA

- Remove the previous default route advertisement on R4.
- Configure an IP SLA instance on R4 to check ICMP reachability to BB3 every five seconds.
- R4 should advertise a default route into OSPF, but only if the SLA
monitoring reports its status as OK.


Conditional default routing by monitoring layer 2 interface state is not a good indication of end-to-end reachability.  A good design is to employ IPL SLA tracking which is more reliable than layer 2 interface status, this provides an accurate end-to-end reachability information.


Rack1R4(config)#ip sla monitor 1
Rack1R4(config-sla-monitor)#type echo protocol ipicmpEcho 204.12.1.254
Rack1R4(config-sla-monitor-echo)#timeout 2000
Rack1R4(config-sla-monitor-echo)#frequency 5
Rack1R4(config-sla-monitor-echo)#exit

Rack1R4(config)#ip sla monitor schedule 1 start-time now life forever

Rack1R4(config)#track 1 rtr 1
Rack1R4(config)#ip route 169.254.0.1 255.255.255.255 null0 track 1

Rack1R4#show track
Track 1
  Response Time Reporter 1 state
  State is Up
    1 change, last change 00:02:35
  Latest operation return code: OK
  Latest RTT (millisecs) 36
  Tracked by:
    STATIC-IP-ROUTING 0

configuring the route-map

Rack1R4(config)#ip prefix-list PLACEHOLDER permit 169.254.0.1/32

Rack1R4(config)#route-map TRACK_PLACEHOLDER
Rack1R4(config-route-map)#match ip address prefix-list PLACEHOLDER

Rack1R4(config)#router ospf 1
Rack1R4(config-router)#default-information originate always route-map TRACK_PLACEHOLDER

before shutting down SW4 fa0/24 on the far-end of the connection.

Rack1R4#show ip ospf database | inc _0.0.0.0
0.0.0.0         150.1.4.4       44          0x80000001 0x00B35F 1
0.0.0.0         150.1.6.6       1152        0x80000002 0x009776 1

Rack1R4#
Rack1R4#show ip route 169.254.0.1
Routing entry for 169.254.0.1/32
  Known via "static", distance 1, metric 0 (connected)
  Routing Descriptor Blocks:
  * directly connected, via Null0
      Route metric is 0, traffic share count is 1

shutting down SW4 fa0/24

Rack1R4#
*Mar  1 01:41:29.419: %TRACKING-5-STATE: 1 rtr 1 state Up->Down

Rack1R4#show ip route 169.254.0.1          
% Network not in table

Rack1R4#show ip ospf database | inc _0.0.0.0
0.0.0.0         150.1.6.6       1288        0x80000002 0x009776 1