Edit: Thanks for playing! You can find the official answer and explanation here.
I had an interesting question come across my desk today which involved a very common area of confusion in OSPF routing logic, and now I’m posing this question to you as a challenge!
The first person to answer correctly will get free attendance to our upcoming CCIE Routing & Switching Lab Cram Session, which runs the week of June 1st 2015, as well as a free copy of the class in download format after it is complete. The question is as follows:
Given the below topology, where R4 mutually redistributes between EIGRP and OSPF, which path(s) will R1 choose to reach the network 18.104.22.168/32, and why?
- What will R2′s path selection to 22.214.171.124/32 be, and why?
- What will R3′s path selection to 126.96.36.199/32 be, and why?
- Assume R3′s link to R1 is lost. Does this affect R1′s path selection to 188.8.131.52/32? If so, how?
Tomorrow I’ll be post topology and config files for CSR1000v, VIRL, GNS3, etc. so you can try this out yourself, but first answer the question without seeing the result and see if your expected result matches the actual result!
Good luck everyone!
About Brian McGahan, CCIE #8593, CCDE #2013::13:
Brian McGahan was one of the youngest engineers in the world to obtain the CCIE, having achieved his first CCIE in Routing & Switching at the age of 20 in 2002. Brian has been teaching and developing CCIE training courses for over 10 years, and has assisted thousands of engineers in obtaining their CCIE certification. When not teaching or developing new products Brian consults with large ISPs and enterprise customers in the midwest region of the United States.
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