Which two configuration changes can you make on edge-1 to allow the two routers to establish adjacency?

Refer to the exhibit.

Router edge-1 is unable to establish OSPF neighbor adjacency with router ISP-1.

Which two configuration changes can you make on edge-1 to allow the two routers to establish adjacency? (Choose two.)
A . Set the subnet mask on edge-1 to 255 255.255.252.
B . Reduce the MTU on edge-1 to 1514.
C . Set the OSPF cost on edge-1 to 1522.
D . Reduce the MTU on edge-1 to 1500.
E . Configure the ip ospf mtu-ignore command on the edge-1 Gi0/0 interface.

Answer: D, E

Explanation:

A situation can occur where the interface MTU is at a high value, for example 9000, while the real value of the size of packets that can be forwarded over this interface is 1500.

If there is a mismatch on MTU on both sides of the link where OSPF runs, then the OSPF adjacency will not form because the MTU value is carried in the Database Description (DBD) packets and checked on the other side.