OSPF Flashcards
In OSPF LFA FRR, what are the 9 tie-breakers in order of priority?
- SRLG
- Interface Protection
- Broadcast Interface Protection
- Node Protection
- Downstream Path
- Linecard Disjoint Interfaces
- Metric
- ECMP Primary
- ECMP Secondary
What does SRLG stand for?
Shared Risk Link Group
What is the LFA FRR attribute Interface Protection
Don’t select the same outgoing interface as the primary path.
What is the LFA FRR Broadcast Interface Protection?
Don’t select backup paths that use the same broadcast network as the primary path.
What is the LFA FRR Node Protection?
Don’t select a backup path that uses the same next-hop router as your primary path
What is the LFA FRR tie-breaker Downstream Path?
Similar to the EIGRP feasible successor rule. A neighbor should have a smaller metric to the destination as the total metric of our primary path.
What is LFA FRR tie-breaker Line-card Disjoint Interfaces?
Similar to SRLGs, don’t use backup paths that use the same line card as the primary path.
What is the LFA FRR Tie-breaker Metric?
The best backup path might not be the one with the lowest metric next to the primary path, which is why we have all these tie breaker attributes. However, you can still use the lowest metric as one of the tie breakers
What is the LFA FRR Tie-breaker ECMP-Primary?
Prefer a backup path that is part of ECMP (equal cost multipath).
What is the LFA FRR Tie-breaker ECMP-Secondary?
Prefer a backup path is not part of ECMP. This can be useful if a single link in ECMP is unable to handle all traffic. Imagine you have 2x 100 Mbit interfaces carrying about 150 Mbit of traffic. When one of the links fails, a single link will be unable to transmit everything. In this case, it’s best not to use the remaining link of the ECMP as a backup path.
