Exam 300-410 topic 1 question 51 discussion

The subnet 10.1.1.1/24 is redistributed into EIGRP domain so it will have the Administrative Distance (AD) of 170. Therefore R4 also learns about this subnet advertised from R2 with the same AD of 170.In the other hand, subnet 10.1.1.0/24 is also redistributed into OSPF on R3 so R5 & R4 will learn about this subnet with AD of 110, which is better than the above AD of 170 so R4 will choose path R4 -> R5 -> R3 -> R2 -> R1. In order to solve this problem, we can configure an outbound distribute list on R5 to prevent (filter out) this subnet from advertising to R4. Then R4 only has one way to reach R1, which is R4 -> R2 -> R1. But this method will remove the backup route so it is not the best solution.Another solution is to reduce the AD of the external EIGRP to a value smaller than 110. This method reserves the backup route in case of the main route fails

A is correct

Option A: Changing the administrative distance of the external EIGRP routes to 90 ensures these routes are preferred over OSPF routes, preventing suboptimal routing. This method directly addresses the issue by prioritizing EIGRP routes appropriately within the routing table. Option B: Applying an outbound distribution list on R5 towards R4 in OSPF could potentially filter routes, but the option lacks clarity on how it would achieve the desired outcome. Without specific details, it's less straightforward and reliable compared to adjusting the administrative distance, which is a clear and direct solution. Therefore, Option A is the most clear and effective approach to resolve the suboptimal path issue.

A. Change the administrative distance of the external EIGRP to 90. B. Apply the outbound distribution list on R5 toward R4 in OSPF. C. Change the administrative distance of OSPF to 200 on R5. D. Redistribute OSPF into EIGRP on R4. A: If we change AD or ext-EIGRP on R4 to 90, R4 now prefers path trhough R4. --> Correct B: This works. Now we have no backup path. And what if more prefixes are redistributed on R1? C:Administrative Distance is locally significant on the router D:This won't solve the problem, of OSPF having better AD (110) than external EIGRP (170)

Why not C?

R4#trac 10.1.1.1 Type escape sequence to abort. Tracing the route to 10.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 10.1.24.2 2 msec 2 msec 2 msec 2 10.1.12.1 2 msec * 2 msec R4#sh run | sec router eigrp router eigrp 1 network 10.1.24.0 0.0.0.255 redistribute ospf 1 metric 1000000 1 255 1 1500 route-map FILTER-TAG distance eigrp 90 90 R4#

There are two routes on P4: D EX (ad170) towards R2 O E2 (ad110) towards R5 (suboptimal path) What needs to be done so that the packet goes towards R2, if a smaller administrative distance is preferable.

A is correct,

All of the routers in the same OSPF area need to have the same exact LSDB. You cannot have it any other way in ospf. So B is wrong. You could implement a local distribute list on R4 to filter it locally from the RIB (still being in the LSDB), but I dont think this is THE BEST fix. The best fix is to maintain the backup route thru R5 and just lower the AD of external EIGRP to anything below 110.

B is right， after “”redistributes EIGRP into OSPF on R3 “,the administrative distance of "10.1.1.0/24 network"in ospf is 110. R4 has 2 path2 to "10.1.1.0/24 network": R4-->R2: eigrp AD 170( because it is from "redistribute connected"commad on R1) R4-->R5: OSPF AD 110(all AD value is "110 "in ospf including redistributed) So it will choose R5-R4 B has no effect for LSA,right? A is right: R4(config)#router eigrp 1 R4(config-router)#distance eigrp 90 90

The given answer is correct

The given answer is correct external eigrp 170 ------> 90 ospf 110 ------> 110 the route is external eigrp because it is redistributed in.

A is correct, 10. subnet is redistributed to eigrp so its treated as external route with defaul AD of 170

B is the correct answer. Make sure that R4 is already having the internal EIGRP route through R2. Outbound distribute-list on R5 is required to stop exporting the external routes to R4 i.e. learned from R3.

I dont think that R4 will ever take route from R5 since it should be learning internal EIGRP route for the destination route using AD value of 90 and OSPF AD value should be 110.