OSPF

Prefix Suppression

Used to cut down on the size of the LSDB and routing table by filtering out transit links. It is enabled with just one command either at the process level or interface level.

When enabled it does not filter out:

  • Loopback
  • Secondary IP addresses
  • Passive Interfaces

It does however filter out stub network (Type 3 link) information from the router LSA when this sub network also has a link to another router. And for the network LSA it sets the subnet maks to /32

You could see the prefix suppression as a security mechanism, because when enabled you do not attract traffic to the transit routers as you do not have reachability information for these.

Configuration of Prefix Suppression

Like I said it is a one line config:

router ospf 1
 prefix-suppression

or for interface specific config:

interface e0/0
 ip ospf prefix-suppression [disable]