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Frame Relay Configuration 553

When the network is truly fully meshed, point-to-point subinterfaces can be used. This is
typically chosen to maintain consistency with other Frame Relay networks elsewhere in
the network that are not fully meshed. This choice requires a larger number of IP subnets
to be used.

When the network contains some fully meshed portions (for example, when 3 sites have
VCs between each other but the other 10 do not), a multipoint subinterface can be used
for the fully meshed portion and point-to-point subinterfaces can be used for the rest.

When the network contains some fully meshed portions (for example, when 3 sites have
VCs between each other but the other 10 do not), using only point-to-point subinterfaces
is another option. This requires more IP subnets and IPX networks than when using a
multipoint subinterface for the fully meshed portion of the network.

Many sites avoid confusion by always using point-to-point subinterfaces to maintain
consistency.

Correlating the DLCI(s) to their subinterfaces is required when using either type of
subinterface. LMI enquiry messages notify the router that PVCs are active; the router then
needs to know which subinterface uses the DLCI. An individual DLCI is used by only one
subinterface. For a point-to-point subinterface, only one DLCI is used; for multipoint, many
DLCIs are used.

Three samples of Layer 3 addressing were used earlier in the chapter, with the networks
diagrammed in Figure 8-11, Figure 8-12, and Figure 8-13. The configurations matching those
networks and addresses are shown next.

Configuring Networks Without Subinterfaces

The first sample network (based on the environment depicted in Figure 8-11) does not use
subinterfaces. Example 8-4, Example 8-5, and Example 8-6 show the configuration for this
network.

Example 8-4

Mayberry Configuration

ipx routing 0200.aaaa.aaaa
!
interface serial0
encapsulation frame-relay
ip address 199.1.1.1 255.255.255.0
ipx network 199
!
interface ethernet 0
ip address 199.1.10.1 255.255.255.0
ipx network 1
!
router igrp 1
network 199.1.1.0
network 199.1.10.0

ch08.fm Page 553 Monday, March 20, 2000 5:17 PM