300-410 · Question #32
Refer to the exhibit. The output of the trace route from R5 shows a loop in the network. Which configuration prevents this loop?
The correct answer is A. R3 router ospf 1 redistribute eigrp 1 subnets route-map SET-TAG ! route-map SET-TAG permit 10 set tag 1 R4 router eigrp 1 redistribute ospf 1 metric 2000000 1 255 1 1500 route-map FILTER-TAG ! route-map FILTER-TAG deny 10 match tag 1 ! route-map FILTER-TAG permit 20. This configuration prevents routing loops during mutual redistribution by tagging routes originating from EIGRP as they enter OSPF, and then filtering these tagged routes if they attempt to re-enter EIGRP via another redistribution point.
Question
Exhibit
Options
- AR3 router ospf 1 redistribute eigrp 1 subnets route-map SET-TAG ! route-map SET-TAG permit 10 set tag 1 R4 router eigrp 1 redistribute ospf 1 metric 2000000 1 255 1 1500 route-map FILTER-TAG ! route-map FILTER-TAG deny 10 match tag 1 ! route-map FILTER-TAG permit 20
- BR3 router eigrp 1 redistribute OSPF 1 route-map SET-TAG ! route-map SET-TAG permit 10 set tag 1 R4 router eigrp 1 redistribute ospf 1 metric 2000000 1 255 1 1500 route-map FILTER-TAG ! route-map FILTER-TAG deny 10 match tag 1 ! route-map FILTER-TAG permit 20
- C
- D
How the community answered
(38 responses)- A63% (24)
- B11% (4)
- C5% (2)
- D21% (8)
Why each option
This configuration prevents routing loops during mutual redistribution by tagging routes originating from EIGRP as they enter OSPF, and then filtering these tagged routes if they attempt to re-enter EIGRP via another redistribution point.
R3 redistributes EIGRP routes into OSPF and applies 'tag 1' to them. R4 then redistributes OSPF routes into EIGRP but denies any routes that have 'tag 1'. This prevents EIGRP-originated routes from being learned by R3, passing through OSPF, and then being re-injected back into EIGRP by R4, thus breaking a potential routing loop for EIGRP-originated routes.
The configuration in Option B tags OSPF routes when redistributing them into EIGRP on R3, and then R4 attempts to filter OSPF routes with that tag when redistributing OSPF into EIGRP. This is less effective because the tag would not typically persist across the OSPF domain itself for R4 to correctly filter routes based on R3's earlier tagging action within the OSPF-to-EIGRP redistribution context.
This choice is empty and cannot be correct.
This choice is empty and cannot be correct.
Concept tested: Routing loop prevention with route tagging during redistribution
Source: https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/13600-redistribute.html
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