OSPF - Demand Circuit and Flood reduction

R6
interface FastEthernet0/1
 ip address 56.0.0.6 255.255.255.0
 ip ospf demand-circuit

R5

interface FastEthernet0/1
 ip address 56.0.0.5 255.255.255.0
 ip ospf demand-circuit

R6

R6#sh ip ospf int fa0/1

FastEthernet0/1 is up, line protocol is up

  Internet Address 56.0.0.6/24, Area 3, Attached via Interface Enable

  Process ID 10, Router ID 66.6.6.6, Network Type BROADCAST, Cost: 10

  Topology-MTID    Cost    Disabled    Shutdown      Topology Name

        0           10        no          no            Base

  Enabled by interface config, including secondary ip addresses

  Configured as demand circuit

  Run as demand circuit

  DoNotAge LSA allowed

Hello due in 00:00:07

Suppress hello for 0 neighbor(s)

R5

FastEthernet0/1 is up, line protocol is up

  Internet Address 56.0.0.5/24, Area 3, Attached via Network Statement

  Process ID 10, Router ID 55.5.5.5, Network Type BROADCAST, Cost: 10

  Topology-MTID    Cost    Disabled    Shutdown      Topology Name

        0           10        no          no            Base

  Configured as demand circuit

  Run as demand circuit

  DoNotAge LSA allowed

Hello due in 00:00:06

Suppress hello for 0 neighbor(s)

R5 

Sh ip ospf nei

R5#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface

1.1.1.1           1   FULL/DR         00:00:36    15.0.0.1        FastEthernet2         /0

2.2.2.2           1   FULL/DR         00:00:37    25.0.0.2        FastEthernet0         /0

66.6.6.6          1   FULL/BDR        00:00:37    56.0.0.6        FastEthernet0         /1

In order to suppress HELLO packets, let's change the OSPF network type. The lack
of periodic hello exchange will be visible also in the show ip ospf neighbor output,

R5 & R6

Int fa0/1

ip ospf network point-to-point

now

R5#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface

1.1.1.1           1   FULL/DR         00:00:34    15.0.0.1             FastEthernet2/0

2.2.2.2           1   FULL/DR         00:00:35    25.0.0.2            FastEthernet0/0

66.6.6.6          0   FULL/  -                -             56.0.0.6           FastEthernet0/1

R5#

we can see dead time is not visible for neighborship with R6 & R5

R6#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface

55.5.5.5          0   FULL/  -           -        56.0.0.5        FastEthernet0/1

R6#

  

R6

FastEthernet0/1 is up, line protocol is up

  Internet Address 56.0.0.6/24, Area 3, Attached via Interface Enable

  Process ID 10, Router ID 66.6.6.6, Network Type POINT_TO_POINT, Cost: 10

  Topology-MTID    Cost    Disabled    Shutdown      Topology Name

        0           10        no          no            Base

  Enabled by interface config, including secondary ip addresses

  Configured as demand circuit

  Run as demand circuit

  DoNotAge LSA allowed

  Transmit Delay is 1 sec, State POINT_TO_POINT

:::::::::::

Hello due in 00:00:02

::::::::::

  Adjacent with neighbor 55.5.5.5  (Hello suppressed)

  Suppress hello for 1 neighbor(s)

Case -2 To stop periodic paranoid update LSA flooding in area 3.

The main difference between flooding reduction and demand circuits is that former suppresses only periodic LSA refreshes; it does not suppress periodic hello packets. Thus, the flooding reduction feature does not impair the detection of a neighbor router going down.

R5 & R6

interface FastEthernet0/1

 ip ospf network point-to-point

 ip ospf flood-reduction

 duplex auto

in R6

FastEthernet0/1 is up, line protocol is up

  Internet Address 56.0.0.6/24, Area 3, Attached via Interface Enable

  Process ID 10, Router ID 66.6.6.6, Network Type POINT_TO_POINT, Cost: 10

  Topology-MTID    Cost    Disabled    Shutdown      Topology Name

        0           10        no          no            Base

  Enabled by interface config, including secondary ip addresses

  Reduce LSA flooding.