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Exam 300-410 topic 1 question 256 discussion

Actual exam question from Cisco's 300-410

Question #: 256
Topic #: 1

Refer to the exhibit. An administrator configures a router to stop using a particular default route if the DNS server 8.8.8.8 is not reachable through that route.
However, this configuration did not work as desired and the default route still works even if the DNS server 8.8.8.8 is unreachable. Which two configuration changes resolve the issue? (Choose two.)

A. Use a separate track object to reference the existing IP SLA 1 probe for every static route.
B. Use a separate IP SLA probe and track object for every static route.
C. Associate every IP SLA probe with the proper WAN address of the router.
D. Reference the proper exit interfaces along with the next hops in both static default routes.
E. Configure two static routes for the 8.8.8.8/32 destination to match the IP SLA probe for each ISP.

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Suggested Answer: BC 🗳️

by NoUserName1234 at Oct. 14, 2022, 10:32 a.m.

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Lilienen

Highly Voted 2 years, 4 months ago

Selected Answer: BC

Correct: B - Both static routes must have a separate Track object and IP SLA probe. C - Each SLA probe must originate from a different ISP, therefore a different IP address. Wrong: A - Only a separate Track object won't help with anything, we need also a separate IP SLA probe. D - This is redundant, the router knows which interface to use for both next hops (based on ARP and MAC address table). E - This is just messy and not needed, we just need to set a different source for each probe (answer C).

upvoted 8 times

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XBfoundX

Most Recent 4 months, 4 weeks ago

Selected Answer: BC

Maybe someone get confused about this cause they are seeing the community post. But there is a why they use the /32 route: "The first two static routes are there to make sure that the tested IP address inside the ISP1 is truly reached only via link to ISP1, and if that link is down, then the pings are going to be thrown away (this is to prevent pinging 8.8.8.8 via ISP2 thanks to the default route)." The key point is that they want that only ISP1 is going to reach 8.8.8.8 so we want that if that specific route is not reachable they will fallback to the second default route but they will no be able to contact 8.8.8.8 cause there is a null0 route because this is on purpose

upvoted 1 times

XBfoundX

4 months, 4 weeks ago

BUT in our scenario here we are just saying that the track is not working. For let this work we just create two IP SLA objects, and two different track, each object is gonna use the ISP1 and ISP2 interface. If from that interface the 8.8.8.8 is not reachable then the track will go down. There is no need for using a static /32 route, cause we already reach the 8.8.8.8 via the default route.

upvoted 1 times

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kldoyle97

7 months, 1 week ago

Selected Answer: BC

A -> No, separate probes and track objects for each static route B -> Correct C -> Correct, if we configured the probe as: icmp-echo 8.8.8.8 source-ip <RoutersWANaddress> D -> No, including the egress interface is redundant E -> No, there is nothing wrong with the current static routes besides the attached track objects

upvoted 1 times

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[Removed]

11 months, 2 weeks ago

Selected Answer: BC

im going with B & C

upvoted 1 times

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Almylle

2 years ago

Selected Answer: BC

Im going for B and C, because the alternative E it's isn't needed, with the default route u already have communication with google DNS, so you only need to separate the tracks between static routes and WAN's

upvoted 2 times

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HungarianDish_111

2 years ago

It is not clearly described what they want to configure with "E". It could be a valid option with the correct configuration. Based on this: https://community.cisco.com/t5/routing/ip-sla-tracking-a-far-ip/td-p/1971337 The first two static routes are there to make sure that the tested IP address inside the ISP1 is truly reached only via link to ISP1, and if that link is down, then the pings are going to be thrown away (this is to prevent pinging 8.8.8.8 via ISP2 thanks to the default route). ip route 8.8.8.8 255.255.255.255 Ethernet0/0 10.0.0.1 ip route 8.8.8.8 255.255.255.255 Null0 2 ip sla 1 icmp-echo 8.8.8.8 source-interface Ethernet0/0 threshold 800 timeout 1000 frequency 30 ip sla schedule 1 start-time now life forever track 1 rtr 1 reachability ip route 0.0.0.0 0.0.0.0 10.0.0.1 track 1 ip route 0.0.0.0 0.0.0.0 20.0.0.1 2

upvoted 1 times

HungarianDish_111

2 years ago

This way, a static route to 8.8.8.8/32 should be set only via primary ISP. Not for both ISPs. This makes "E" incorrect.

upvoted 1 times

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Pietjeplukgeluk

1 year, 5 months ago

Question: "icmp-echo 8.8.8.8 source-interface Ethernet0/0" Would the device in this case only use the source IP of the interface or only allow packets going outbound (so if a route lacks, the packets will not even be send outbound). Anyway, in my opinion there is a difference between a route, a source interface and the actual route used for the test icmp packet. Anyway, i guess i need to lab this one to really understand how the source-interface part behaves.

upvoted 1 times

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ellen_AA

2 years, 5 months ago

D & E are correct

upvoted 2 times

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Huntkey

2 years, 8 months ago

Selected Answer: BC

I would vote for B and C. Setting the static route to 8.8.8.8 for both ISP doesn't make sense. It would make sense if it is only one static route for that.

upvoted 3 times

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NoUserName1234

2 years, 8 months ago

https://community.cisco.com/t5/routing/ip-sla-tracking-a-far-ip/td-p/1971337

upvoted 2 times

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