Frame Relay Applications: TCP/IP Suite - Page 2

 By Cisco Press
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A fully meshed Frame Relay network can be treated as a VLAN or a single IP subnet. As illustrated in Figure 15-17, three end nodes, each with an IP address assigned, are interconnected across the Frame Relay network via the Frame Relay interface on each FRAD/router. Each of these addresses shares the same network and subnet numbers, with only the host portion of the address differing.

It is worth noting that in this configuration, each Frame Relay interface is supporting multiple VCs with only a single IP address assigned to that interface, in a broadcast configuration. Another common Frame Relay configuration would have an IP address for each VC on the Frame Relay interface. This is enabled by the use of subinterfaces and will be discussed in more detail later in this chapter.

Figure 15-18 reflects the addition of a fourth router (Router D) with a different IP address from the rest of the subnet assigned to the Frame Relay interface. Router D is not part of the full mesh because it is only connected to Router B. Because Router D is part of a different subnet, new IP addresses are assigned to each endpoint of the permanent virtual circuit (PVC).


Figure 15-18: Frame Relay with Two IP Subnets
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(Click image for larger view in a new window)

In summary, the following rules apply when dealing with Frame Relay implementations using virtual IP subnets:

  • A single IP address can be assigned to the entire Frame Relay interface
  • When one or more DLCIs are used requiring the use of subinterfaces, each subinterface is assigned an IP address.

This article was originally published on Jan 30, 2002
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