Refer to the exhibit. An engineer is troubleshooting a routing loop on the network to reach the 172.16 3.0/16 from the OSPF domain. Which configuration on router R1 resolves the issue?
please note B and C does not have "route-map LOOPFILT permit 20" so they will block all routes not defines under access-list 15, and make both B&C wrong.
Routes from 172.16.0.0/16 need to be redistributed from EIGRP to OSPF (under OSPF process), so R5 get's also those routes - However 172.16.0.0/16 does not need to be redistributed from OSPF to EIGRP (under EIGRP process). This will make D the correct one as it filters redistrubtion form OSPF to EIGRP, blocking routes that where originally advertised by EIGRP to OSPF be redistrubted from OSPF to EIGRP.
I think the answer should be D, where EIGRP redistributes routes from OSPF by excluding the route originated from itself "172.16.0.0/16" and make routes known to each other side as well. The rest 3 answers don't look to make sense with rejecting the subnet "172.16.0.0/16" when OSPF learning from EIGRP, this way makes 172.16.3.0/16 unreachable from OSPF domain.
we can deny redistribution into OSPF from EIGRP on R1, but there is no redundant path now.
The traceroute implies a loop in the EIGRP domain, answer = D
How to solve:
172.16.3.0 is external route redistributed into OSPF domain with AD 170.
I set up GNS3 lab with router R6 connected to R3, and redistributed this externally on R6 to test the traceroute.
172.16.3.0 has AD 170 on both routers R1 and R2. Depending on who redistributes into OSPF first, the other router sees 172.16.3.0 with an AD 110. Example I redistribute on R3 first R1 sees it as OSPF route instead of EIGRP.
show ip route: 172.16.0.0/24 is subnetted, 1 subnets
O E2 172.16.3.0 [110/20] via 1.5.0.5, 00:02:24, Ethernet0/1
Now R1 redistributes this route back into EIGRP.
R3 has two routes to reach this subnet.
In my GNS3 R6 to R3 link is 1.1.3.0/24 and R3 to R1 link is 1.3.0.0/24
R3
show ip route eigrp
172.16.0.0/24 is subnetted, 1 subnets
D EX 172.16.3.0 [170/2560025856] via 1.3.0.1, 00:06:06, Ethernet0/0
[170/2560025856] via 1.1.3.1, 00:06:06, Ethernet0/2
Admin keeps cutting off all my suggestions short; whatever I labbed this. 172.16.3.0 is external route and showing up as AD 170 in both directions on R3 this is why there's a loop.
How to solve: route-tagging, summary addresses, or eigrp distance command
We need to filter 172.16.3.0 from redistribute in ospf (my opinion is A please verify)
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