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Frame Relay Protocols 547
will not work on Frame Relay because there is no support for broadcasts. Therefore, ARP
cannot be used to discover that DLCI.
Two solutions exist by which Router A can learn the mapping between Router B's IP address
and DLCI. One uses a statically configured mapping, and the other uses a dynamic process
called Inverse ARP.
Table 8-20 lists the IP and IPX addresses of the three routers in Figure 8-16.
Example 8-3 lists the static Frame Relay map for the three routers in Figure 8-16. The DLCIs
in Table 8-20 are the same as those used in Figure 8-16.
Consider the case in which Gary makes an FTP connection to Brice. The frame-relay map
command for Router A referencing 10.1.2.2 would be used for packets originating from Gary
and going to Brice. Conversely, a packet sent back from Brice to Gary would cause Router B
to use its map statement referring to Router A's IP address of 10.1.2.1. Mapping is needed for
Table 8-20
Layer 3 Addresses and DLCIs Used with Figure 8-16
Router
Global DLCI
IP Address
IPX Address
A
40
10.1.2.1
2.0200.aaaa.aaaa
B
41
10.1.2.2
2.0200.bbbb.bbbb
C
42
10.1.2.3
2.0200.cccc.cccc
Example 8-3
frame-relay map Commands
Router A:
interface serial 0
frame-relay map ip 10.1.2.2 41 broadcast
frame-relay map ipx 2.0200.bbbb.bbbb 41 broadcast
frame-relay map ip 10.1.2.3 42 broadcast
frame-relay map ipx 2.0200.cccc.cccc 42 broadcast
Router B:
interface serial 0
frame-relay map ip 10.1.2.1 40 broadcast
frame-relay map ipx 2.0200.aaaa.aaaa 40 broadcast
frame-relay map ip 10.1.2.3 42 broadcast
frame-relay map ipx 2.0200.cccc.cccc 42 broadcast
Router C:
interface serial 0
frame-relay map ip 10.1.2.1 40 broadcast
frame-relay map ipx 2.0200.aaaa.aaaa 40 broadcast
frame-relay map ip 10.1.2.2 41 broadcast
frame-relay map ipx 2.0200.bbbb.bbbb 41 broadcast
ch08.fm Page 547 Monday, March 20, 2000 5:17 PM