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Integrated Routing Protocols 413
The configuration is simplified if you concentrate on the transport, encapsulation, and
passenger protocols. First, as highlighted in Example 6-22, IP is enabled on all interfaces except
the tunnel interface. However, the tunnel source command implies the IP address to be used
on the interface; this IP address is used as the source for all packets sent out the tunnel interface.
Likewise, the tunnel destination IP address is used as the destination address for packets sent
out each tunnel interface. IP is enabled by default.
The encapsulation protocol in this case has defaulted to generic route encapsulation (GRE). If
another protocol were desired, the tunnel mode interface subcommand would be used to set
the protocol. (While the details of the encapsulation protocols are likely to be beyond the CCNA
requirements, the other types are aurp, cayman, dvmrp, eon, ipip, iptalk, and nos.)
The passenger protocol is enabled on the tunnel interface, just as it would be for any other
interface. IPX routing is enabled globally, and the ipx network command is used on both the
Ethernet interface and the tunnel interface. Notice the absence of the ipx network command on
Router A's serial 0 interface and Router D's Token Ring interface. Because there are no Novell
nodes in the center of the network, there is no need to enable IPX on these interfaces.
Integrated Routing Protocols
So far, all the routing protocol functions discussed in this book fall under the classification of
separate multiprotocol routing. To fully compare and contrast the meaning of this term with the
alternative methods of integrated multiprotocol routing, a review of multiprotocol routing is in
order. Consider Figure 6-18, which should remind you of one such concept.
As discussed in Chapter 3, the router determines what type of Layer 3 packet is inside the
received frame. There is a separate routing table for each routable or routed protocol. (If you
previously skipped Chapter 3, you may want to review the generalized routing algorithm, or the
"Ting and Ted" story.) The routing decision is therefore dependent on a routing table specific
for that one Layer 3 protocol. This process is called multiprotocol routing.
Routing protocols fill the routing tables of the various Layer 3 protocols. Although not covered
elsewhere in this book, AppleTalk uses yet another derivative of XNS RIP, called the Routing
Table Maintenance Protocol (RTMP), as its routing protocol. Consider the simple network in
Figure 6-19 and the routing updates that are sent out S0 by Router1.
ipx network 2
!
interface tunnel 3
tunnel source 10.1.5.4
tunnel destination 10.1.1.1
ipx network 3
!
router igrp 9
network 10.0.0.0
Example 6-23
Router D Tunnel Configuration (Continued)
ch06.fm Page 413 Monday, March 20, 2000 5:11 PM