OSPF chooses routes in which order, regardless of route’s administrative distance and metric?(choose six)
A. Intra-Area (O)
B. Inter-Area (O IA)
C. External Type 1 (E1)
D. External Type 2 (E2)
E. NSSA Type 1 (N1)
F. NSSA Type 2 (N2)
Which order, regardless of route’s administrative distance and metric?
This is the correct Question
QUESTION 240
OSPF chooses routes in which order, regardless of route’s administrative distance and metric?
A. Intra-Area (O) – Inter-Area (O IA) – External Type 1 (E1) – External Type 2 (E2) – NSSA Type 1 (N1) –
NSSA Type 2 (N2)
B. Intra-Area (O) – Inter-Area (O IA) – NSSA Type 1 (N1) – NSSA Type 2 (N2) – External Type 1 (E1) –
External Type 2 (E2)
C. Intra-Area (O) – Inter-Area (O IA) – NSSA Type 1 (N1) – External Type 1 (E1) – NSSA Type 2 (N2) –
External Type 2 (E2)
D. Intra-Area (O) – NSSA Type 1 (N1) – External Type 1 (E1) – Inter-Area (O IA) – NSSA Type 2 (N2) –
External Type 2 (E2)
E. Intra-Area (O) – Inter-Area (O IA) – NSSA Type 1 (N1) – External Type 1 (E1) – NSSA Type 2 (N2) –
External Type 2 (E2)
F. NSSA Type 1 (N1) – NSSA Type 2 (N2) – Intra-Area (O) – Inter-Area (O IA) – External Type 1 (E1) –
External Type 2 (E2)
Correct Answer being:
A. Intra-Area (O) – Inter-Area (O IA) – External Type 1 (E1) – External Type 2 (E2) – NSSA Type 1 (N1) –
NSSA Type 2 (N2)
Is this drag and drop question ?
N1 and E1 will never appear in the same routing table in a particular area
N1 is LSA type 7
E1 is LSA type 5.
LSA type 7 only appear in NSSA area, when it gets out of this area, it will change to E1.
This question does not make sense.
depends on the RFC
Abstract from RFC 3101 Section 2.5
(e) If the current LSA is functionally the same as an
installed LSA (i.e., same destination, cost and non-zero
forwarding address) then apply the following priorities in
deciding which LSA is preferred:
1. A Type-7 LSA with the P-bit set.
2. A Type-5 LSA.
3. The LSA with the higher router ID.
Question…what if there’s not P-bit set??!?!?
makes sense to me….https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/212608-ospf-external-path-selection-external-t.pdf
Otherwise, compare the cost of this new AS external path
to the ones present in the table. Note that type-5 and
type-7 routes are directly comparable. Type-1 external
paths are always shorter than Type-2 external paths.
Type-1 external paths are compared by looking at the sum
of the distance to the forwarding address/ASBR and the
advertised Type-1 paths (X+Y). Type-2 external paths are
compared by looking at the advertised Type-2 metrics,
and then if necessary, the distance to the forwarding
address/ASBR.
When a type-5 LSA and a type-7 LSA are found to have the
same type and an equal distance, the following priorities
apply (listed from highest to lowest) for breaking the tie.
Correct Answer: ABECFD.
https://networklessons.com/ospf/ospf-path-selection-explained/
Hello Imen,
OSPF doesn’t make a difference between inter-area or intra-area external routes. It doesn’t matter where the external route originated, it’s the cost that makes the difference.
When I booted up this lab again, I did find something interesting. When I wrote this lesson, I used IOS 12.4 and this is the list that OSPF uses for path selection:
Intra-Area (O)
Inter-Area (O IA)
External Type 1 (E1)
NSSA Type 1 (N1)
External Type 2 (E2)
NSSA Type 2 (N2)
Since Cisco IOS release 15.1(2)S, Cisco uses the path selection order from RFC 3101 which obsoletes RFC 1587. What this means is that it prefers N1 routes before E1 and N2 over E2 routes. In other words, the preferred path now is:
Intra-Area (O)
Inter-Area (O IA)
NSSA Type 1 (N1)
External Type 1 (E1)
NSSA Type 2 (N2)
External Type 2 (E2)
So if you have an N1 route and an E1 route, it doesn’t matter where those originated…OSPF will prefer the N1 route (if you run at least IOS 5.1(2)S 😀
Hope this helps!
Rene
This confuses me, how to know if A-B-C-E-D-F or ABECFD?