Path preference

General information on “OSPF Path Preference”:

• The “type of path” is the first factor which OSPF considers in its path preference
• Since Cisco IOS release 15.1.(2)S OSPF RFC 3101 will be used
• This means OSPF prefers paths in the following order:
  • O: Intra-Area
    • Route within an area
  • O*IA: Inter-Area
    • Router between two areas
  • O*N1: NSSA Type 1
    • External route with increasing metric inside an NSSA
    • Will be converted to E1 type route when passing through an ABR
  • O*E1: External Type 1
    • External route with increasing metric when it traverses the network
  • O*N2: NSSA Type 2
    • External route with “hardcoded” (not changing) metric inside an NSSA (default = 20)
    • Will be converted to E2 type route when passing through an ABR
    • Although the metric is hardcoded, the metric to the ASBR (forward metric) is still relevant within the OSPF domain if there are multiple paths/ASBRs for a given external route
  • O*E2: External Type 2
    • External route with “hardcoded” (not changing) metric (default = 20)
    • Although the metric is hardcoded, the metric to the ASBR (forward metric) is still relevant within the OSPF domain if there are multiple paths/ASBRs for a given external route