Categories R&S

OSPF – Optimize convergence and scalability – Miscellaneous features

Let’s wrap up the OSPF series with some features that are less common but might still be ask during the CCIE LAB.

 

 

Demand circuit:

Mostly use for on-demand circuit such as ISDN.

With this feature, periodic hellos are suppressed and the periodic refreshes of LSAs are not flooded over the demand circuit.

Periodic refreshes of hello updates, LSA updates, and other protocol overhead are prevented from enabling the on-demand circuit when there is no “real” data to send.

R1(config)#int Ethernet0/0
R1(config-if)#ip ospf demand-circuit

R1#sh ip ospf int Ethernet0/0
Ethernet0/0 is up, line protocol is up
  Internet Address 10.10.1.1/24, Area 0, Attached via Interface Enable
  Process ID 10, Router ID 11.11.11.11, Network Type BROADCAST, Cost: 1
SNIP
  Configured as demand circuit
  Run as demand circuit
  DoNotAge LSA allowed

 

Flooding reduction:

This feature will stop the “paranoid update”.

It stops unnecessary LSA flooding by setting the DoNotAge (DNA) bit in the LSA, so there is no need for periodic refresh.

R1(config)#int Ethernet0/0
R1(config-if)#ip ospf flood-reduction

R1#sh ip ospf int Ethernet0/0
Ethernet0/0 is up, line protocol is up
  Internet Address 10.10.1.1/24, Area 0, Attached via Interface Enable
SNIP
  Enabled by interface config, including secondary ip addresses
  Reduce LSA flooding.

 

 

Resource limiting:

This feature is use to restrict the number of prefixes redistributed in OSPF and the number of LSA in the OSPF database.

R5(config)#router ospf 10
R5(config-router)#max-lsa ?
    Maximum number of non self-generated LSAs this process can
                  receive
R5(config-router)#max-lsa 10
*Feb 25 14:25:32.510: %OSPF-4-OSPF_MAX_LSA_THR: Threshold for maximum number of non self-generated LSA has been reached "ospf 10" - 7 LSAs
*Feb 25 14:25:32.510: %OSPF-4-OSPF_MAX_LSA: Maximum number of non self-generated LSA has been exceeded "ospf 10" - 26 LSAs

R5(config-router)#redistribute maximum-prefix 2
R5#sh ip ospf 10
 Routing Process "ospf 10" with ID 5.5.5.5
SNIP
 Redistributing External Routes from,
    connected, includes subnets in redistribution
    Maximum limit of redistributed prefixes 2
    Threshold for warning message 75%

 

 

That’s all for OSPF.

 

 

Thank you for reading.

 

OSPF – Optimize convergence and scalability – Miscellaneous features