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| 7.6 |  | Integrated IS-IS Operation in a WAN Environment |
| 7.6.3 |  | Frame Relay point-to-point scenario with Integrated IS-IS |

Look at the example of a router network connected over Frame Relay using point-to-point subinterfaces. Each Frame Relay permanent virtual circuit (PVC) is treated as its own point-to-point network, with its own IP addresses. The example is of a hub-and-spoke network topology. It is important to note that the spoke routers are also configured with point-to-point subinterfaces, even though, unlike the hub router, they use only one VC. This is the best practice in general for all routing protocols. It allows further VCs to be added without affecting the existing VC. This practice is imperative for IS-IS. A main interface is a multipoint interface, even if it happens to have only one VC configured. If the single VC were configured under a main interface, IS-IS would treat this as a broadcast network and attempt to elect a DIS. Also, an adjacency would not be established because the multipoint end would send broadcast-network-style Hello PDUs, but the point-to-point end would send point-to-point Hello PDUs.

The hub router configuration is shown in Figure .

The encapsulation type, Frame Relay, is set under the main interface of Serial0/0. No IP or IS-IS configuration is included under the main interface. Three subinterfaces are defined, one for each VC. Each subinterface specifies the following:

- The IP address for that point-to-point link, which is a different subnet for each subinterface.
- Integrated IS-IS, ip router isis, as the routing protocol over that subinterface.
- The VC to use for that point-to-point subinterface, using the frame-relay interface-dlci command. This is the only command needed to enable both IP and CLNS across this VC. The router automatically enables, across this VC, all the protocols that are enabled on the point-to-point subinterface. With this configuration, the subinterface will automatically forward routing updates, as is the case when using the broadcast keyword with a Frame Relay map.

Notice that no Frame Relay maps are used in this scenario, since point-to-point interfaces are used.

The show frame-relay map command displays the status of each Frame Relay VC as follows:

- Status defined means it has been configured on the Frame Relay switch, and active indicates that this VC is operational.
- Type is point-to-point, meaning it has been assigned to a point-to-point subinterface.
- Assigned subinterface, for example, Serial0/0.1
- VC identification, for example, DLCI 100.
- Whether it supports broadcast packets, such as RIP Version 1 routing packets.

The debug isis adj-packet command shows neighbor relationship establishment across one of the subinterfaces, Serial0/0.1, sending and receiving point-to-point IIH PDUs and declaring the adjacency "up". Ongoing Hello conversations for the other subinterfaces are also shown.

| Lab Activity e-Lab Activity: Frame Relay Point-to-Point Scenario with Integrated IS-IS This lab is to use point-to-point subinterfaces in a hub-and-spoke network with IS-IS running.