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s.phillipson
Beginner

OSPF Route Selection based on LSA Types ?

Hi,

Does OSPF determine routes based on LSA Type? For example, if a Router has received two routing updates referring to the same IP subnet from (1) an Intra-Area route, received from an OSPF peer in Area 0 and (2) an External route received from an ASBR redistributing routes into Area 0

how will the Router make its selection?

I am specifically concerned in the situation where you have an OSPF area interconnecting into another AS at two points. Could this scenario result in sub-optimal routing due to a Router sending intra-area data via the other AS (ie. a routing loop being formed resulting in sub-optimal routing).

Regards,

Steve

2 ACCEPTED SOLUTIONS

Accepted Solutions
ruwhite
Rising star

Intr-area routes are always preferred over inter-area routes, and internals are always preferred over externals. So, the preference order is:

Type 1/2

Type 3

Type 7

Type 5

:-)

Russ.W

View solution in original post

Steve,

The best way to put an end to any discussion is to refer back to the RFC (2328). Section 11 under Path-type.

Hope this helps,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

View solution in original post