Exam 350-501 topic 1 question 153 discussion

From Chst's comment (via Cisco Link) "...Both neighbor devices must be configured for session protection or one device must be configured for session protection and the other device must be configured to respond to targeted hellos..." If you build a quick lab between 2 routers (R1 and R2). - when you perform: R1(config)# mpls ldp session protection R2(config)# mpls ldp discovery targeted-hellos accept Then you will see that the targeted hello session will come up. However, if R2 does not accept targeted-hellos than the session protection will not work. From Karen's Comment: if you were to set the timer on both routers, then you would enable session protection on both routers. This will bring up the session: R1(config)# mpls ldp session protection duration 30 R2(config)# mpls ldp session protection duration 30 Although Cisco says that you can enable session protection on 1 router, it also says that the neighbor would need to be configured to accept targeted hellos. In this question we have no way of knowing targeted-hellos are enabled on either router thus, we are left with C being the best option.

If you set the timer (duration) only, then that also implicitly enables session protection. This is a simple one you can lab and see for yourself.

D is correct as explained by chst below Answer C - the duration (they call timer in this question) is an optional item and it does not say that needs to be the same value.

I don't like D, it says either one of the routers, LDP session protection needs to be enabled on both routers. C seems to be more correct, while timers are not necessary, in order to set the timer it is part of the mpls ldp session protection command options.