Refer to exhibits 1 and 2. A company uses a Metro Ethernet (Gigabit Ethernet) dedicated circuit to
communicate between users (subnet B) and servers (subnet A) as shown in Exhibit 1. Both
routers use OSPF to advertise the subnets. During a weekly management meeting, they realize
that the WAN link is oversize. They have been using only 2 Mb/s in the worst-case scenario. So
they propose a new, cheaper WAN connection using a 2-Mb/s Frame-Relay point-to-point link to
interconnect both sites (Exhibit 2). The Frame Relay service provider informs them that multicast
traffic is not allowed to run over the service provider network. Which one of these options is best to
enable the company to establish the OSPF neighbor adjacency?
A.
Use OSPF network broadcast, because it uses unicast to establish a neighbor relationship.
B.
Use OSPF network point-to-multipoint, because it uses unicast to establish a neighbor
relationship.
C.
Use OSPF network point-to-point, because it uses unicast to establish a neighbor relationship.
D.
Use OSPF network point-to-multipoint nonbroadcast, because it establishes a neighbor
relationship using unicast packets.
E.
Use OSPF network nonbroadcast, because it establishes a neighbor relationship using
multicast.
Explanation:
OSPF Point-to-Multipoint Network with Separate Costs per Neighbor
Description
OSPF has two new features related to point-to-multipoint networks. One feature applies to
broadcast networks; the other feature applies to nonbroadcast networks.
On point-to-multipoint, broadcast networks, there is no need to specify neighbors. However, you
can specify neighbors with the neighbor command, in which case you should specify a cost to that
neighbor.On point to multipoint, nonbroadcast networks, you now use the neighbor command to identify
neighbors.
Assigning a cost to a neighbor is optional.
Before this feature, some OSPF point-to-multipoint protocol traffic was treated as multicast traffic.
Therefore, the neighbor command was not needed for point-to-multipoint interfaces because
multicast took care of the traffic. Hellos, updates and acknowledgments were sent using multicast.
In particular, multicast hellos discovered all neighbors dynamically.
However, some customers were using point-to-multipoint on nonbroadcast media (such as classic
IP over ATM), so their routers could not dynamically discover their neighbors. This feature allows
the neighbor command to be used on point-to-multipoint interfaces.
On any point-to-multipoint interface (broadcast or not), the Cisco IOS software assumed the cost
to each neighbor was equal. The cost was configured with the ip ospf cost command. In reality,
the bandwidth to each neighbor is different, so the cost should be different. With this feature, you
can configure a separate cost to each neighbor. This feature applies to point-to-multipoint
interfaces only.
Benefits
You can now configure neighbors on point-to-multipoint interfaces and assign a cost to each
neighbor. These capabilities allow the router to dynamically discover neighbors over nonbroadcast
media and to prefer some routes over others by assigning different costs to neighbors.http://www.cisco.com/en/US/docs/ios/11_3/feature/guide/ospfpmp.html