When you use a Frame Relay point-to-point subinterface, each
subinterface is on its own subnet.
Figure 8-24 shows how to resolve the issues using subinterfaces.
Figure 8-24 Using Subinterfaces with Frame Relay
S0.1 10.1.1.1/24
S0
Logical Interface Physical
Interface
Subnet A
10.1.1.2/24
10.2.2.2/24
10.3.3.4/24
Subnet B
S0.2 10.2.2.1/24
S0.3 10.3.3.1/24
Establishing a WAN Connection with Frame Relay 331
A Frame Relay connection requires that, on a VC, the local DLCI be mapped to a
destination network layer address, such as an IP address. Routers can automatically
discover their local DLCI from the local Frame Relay switch using the LMI
protocol.
On Cisco routers, the local DLCI can be dynamically mapped to the remote router network
layer addresses with Inverse ARP. Inverse ARP associates a given DLCI to the next-hop
protocol address for a speci?¬?c connection. Inverse ARP is described in RFC 1293.
Example: Frame Relay Address Mapping
As shown in Figure 8-25, using Inverse ARP, the router on the left can automatically
discover the remote router IP address and then map it to the local DLCI. In this case, the
local DLCI of 500 is mapped to the 10.
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