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| 7.6 |  | Integrated IS-IS Operation in a WAN Environment |
| 7.6.4 |  | Frame Relay point-to-multipoint scenario with Integrated IS-IS |

In this scenario, all the Frame Relay ports are configured as multipoint interfaces. They are configured either as a multipoint subinterface, on the hub router R4, or as a main interface on the other routers. All interfaces share the same IP subnet in a multipoint configuration. In a multipoint environment with IS-IS, it is important that a full mesh be implemented. Therefore, all other routers will also have VCs interconnecting them, although these are not shown in the diagram. If this were a true hub-and-spoke environment, and the spoke sites had no need to communicate to each other, this topology could work with only the indicated DLCIs. In this case, the hub router must become the DIS for the NBMA network, as it is the only router visible to all others. A suitable IS-IS priority should be set on the Frame Relay interface of the hub router using the isis priority command. Routes would be installed in each spoke router toward the other spoke routers by way of their local IP addresses. However, packets to these destinations would be dropped, as there are no direct VCs between the spokes.

This point-to-multipoint scenario shows the configuration of the multipoint interface on the R4 hub router. In a multipoint environment, IP and CLNS maps must be configured separately. The frame-relay interface-dlci command is used to enable IP across the Frame Relay PVCs. Inverse ARP will automatically resolve the remote end IP addresses. On a point-to-point subinterface, this command enables all traffic, but in a multipoint environment this enables only IP. Alternatively, the IP maps could be entered explicitly using frame-relay map ip <ip address> <dlci>. In this case, the "broadcast" keyword is not necessary for IP, as only directed IP packets will use this VC. To enable CLNS, which must be done separately from IP in a multipoint environment, the frame-relay map clns command is used. CLNS is used for the IS-IS routing packets and therefore the "broadcast" keyword must be specified.
Finally, the same monitoring commands used for the point-to-point example yield slightly different output in the point-to-multipoint environment. The show frame-relay map command again displays the status of each Frame Relay VC. This time separate entries are created as follows for the IP and CLNS mappings, even though they use the same VC:

- The CLNS map shows that it is created as a static map and that "broadcast" was specified.
- The IP map is dynamic because the IP address was resolved by inverse ARP.

The debug isis adj-packet command again shows the neighbor relationship establishment. However this time the adjacency uses LAN IIH PDUs because this is a multipoint environment. Keep in mind that the preferred configuration for Integrated IS-IS in a WAN environment is to configure all interfaces as point-to-point subinterfaces. This avoids the full mesh required with the point-to-multipoint option. The point-to-multipoint option results in weak network stability. Having one PVC go down can have a domino effect on the WAN. This points out one major difference between OSPF and IS-IS configuration.

| Lab Activity e-Lab Activity: Frame Relay Point-to-Multipoint Scenario with Integrated IS-IS This lab is to configure a point-to-multipoint interface with frame-relay and IS-IS.