Excellent and very detailed explanation. I was struggling getting the P and Q knows. Now I have a better understanding. Also, a great point was how to the P4 router calculates what label to push, whether the prefix sid or a adj sid label.
Hi Matthew - In this example, P5 is in the Q-space because it's shortest path from P5 to P9 never traverses the potential broken link between P4 and P5. For the post computed shortest path, it is looking for a node that is in the P space and the Q space. P5 doesn't fit into that category and so it's not on the post computed path.
Hi @Barbara, Thanks for your explanation. I have one question please, why PE2, PE3 are not selected in the Q space knowing that they can reach Dest without passing through the protected link?
@@BarbaraAnne Thanks dear for your reply. But I still think that PE2 can be in Q space :) Please check my below understanding of the topology: - PE3 can reach P9 through (P5--P6--P9) --> PE3 is not in Q space as it passes through P5 (I was wrong in my 1st comment ;) - PE2 can reach P9 through (P6--P9) --> PE2 can be in Q sapce as it is not passing through the protected link P4-P5. Please correct me if I'm wrong Thanks
@@babamohamed452 TI-LFA is trying to find the shortest path so that when the IGP reconverges, it doesn't have to change the Service Path. PE2->P6->P9 has a path cost of 5000+1=5001 whereas P2->P3->P6->P9 has a cost of 1+1+1=3 so that's the route the converged IGP will take. It's possible to take that route but it is not the BEST route because of the link metrics. TI-LFA is trying to find the best route.
Excellent and very detailed explanation. I was struggling getting the P and Q knows. Now I have a better understanding. Also, a great point was how to the P4 router calculates what label to push, whether the prefix sid or a adj sid label.
Thank you!
It's surprising for me to learn your channel. Excellent video. Appreciate it
So nice of you!
Excellent, thanks
Glad you liked it!
Very Good Explanation, Thanks Barbara
Thanks Ashraf!
Great video, congratulations for your very clear explanation
Thanks! Glad you liked it.
Thank you, Barbara. Great Video!
Thank you!
Exactly the explanation I needed! Great 👍
Glad it was helpful!
Hi Barbara, Can you explain why P5 is considered in the Q-space as it is not on the post computed shortest path.
Hi Matthew - In this example, P5 is in the Q-space because it's shortest path from P5 to P9 never traverses the potential broken link between P4 and P5.
For the post computed shortest path, it is looking for a node that is in the P space and the Q space. P5 doesn't fit into that category and so it's not on the post computed path.
Hi @Barbara,
Thanks for your explanation. I have one question please, why PE2, PE3 are not selected in the Q space knowing that they can reach Dest without passing through the protected link?
Hi Mohamed. Their link metrics are 5000 so they are not on a shortest path. The green links have a metric of 1 and the orange have a metric of 5000.
@@BarbaraAnne Thanks dear for your reply. But I still think that PE2 can be in Q space :)
Please check my below understanding of the topology:
- PE3 can reach P9 through (P5--P6--P9) --> PE3 is not in Q space as it passes through P5 (I was wrong in my 1st comment ;)
- PE2 can reach P9 through (P6--P9) --> PE2 can be in Q sapce as it is not passing through the protected link P4-P5.
Please correct me if I'm wrong
Thanks
@@babamohamed452 TI-LFA is trying to find the shortest path so that when the IGP reconverges, it doesn't have to change the Service Path. PE2->P6->P9 has a path cost of 5000+1=5001 whereas P2->P3->P6->P9 has a cost of 1+1+1=3 so that's the route the converged IGP will take. It's possible to take that route but it is not the BEST route because of the link metrics. TI-LFA is trying to find the best route.