Refer to the exhibit. A network administrator reviews the branch router console log to troubleshoot the OSPF adjacency issue with the DR router. Which action resolves this issue?
A.
Stabilize the DR site flapping link to establish OSPF adjacency.
B.
Advertise the branch WAN interface matching subnet for the DR site.
C.
Configure the WAN interface for DR site in the related OSPF area.
D.
Configure matching hello and dead intervals between sites.
B is more appropriate because netmask doesn't match between neighbors
R1#
OSPF: Mismatched hello parameters from 192.168.12.2
OSPF: Dead R 40 C 40, Hello R 10 C 10 Mask R 255.255.255.128 C 255.255.255.0
Now we have something to work with. R1 says it received a hello packet but we have mismatched hello parameters. The R stands for what we received and the C stands for what we have configured.
You can see that there is a mismatch in the subnet mask. R1 is configured with subnet mask 255.255.255.0 while R2 has subnet mask 255.255.255.240. OSPF will only compare the subnet mask when you are using the broadcast network type. You can also spot this error if you look at the OSPF information per interface. Broadcast is using a DR router while point-to-point doesn't use a DR router
After two routers discover each other by receiving Hellos from the other router, the routers
perform the following parameter checks based on the receive Hellos:
■ Must pass the authentication process
■ Must be in the same primary subnet, including the same subnet mask
■ Must be in the same OSPF area
■ Must be of the same area type (regular, stub, not-so-stubby area [NSSA])
■ Must not have duplicate RIDs
■ OSPF Hello and Dead timers must be equal
If any of these items do not match, the two routers simply do not form a neighbor
relationship.
Mismatched hello parameter indicates that the packet came with a wrong parameter in this case the mask addresses. timers are ok, I just lab it and get the same logs on the debug.
00:07:18: OSPF: Mismatched hello parameters from 10.1.1.1
00:07:18: OSPF: Dead R 40 C 40 Hello R 10 C 10 Mask R 255.255.255.0 C 255.255.255.240
00:07:28: OSPF: Rcv hello from 192.168.1.1 area 0 from GigabitEthernet0/0 10.1.1.1
00:07:28: OSPF: Mismatched hello parameters from 10.1.1.1
00:07:28: OSPF: Dead R 40 C 40 Hello R 10 C 10 Mask R 255.255.255.0 C 255.255.255.240
00:07:38: OSPF: Rcv hello from 192.168.1.1 area 0 from GigabitEthernet0/0 10.1.1.1
00:07:38: OSPF: Mismatched hello parameters from 10.1.1.1
00:07:38: OSPF: Dead R 40 C 40 Hello R 10 C 10 Mask R 255.255.255.0 C 255.255.255.240
The logs indicate a Mismatched Hello Parameter; however, WHICH parameter is mismatched?
Dead: R=40 C=40
Hello: R=10 C=10
Mask: R= -.0 C= -.240
It is the Subnet Masks that do not match. Answer is B.
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