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300 Chapter 5: Network Protocols
(1.0200.1111.1111, in this case). Of course, the routers need network 1000 in their IPX routing
tables. For example, Table 5-31 shows the contents of the IPX routing table of R3:
R3 learned the routes to Network 3 and Network 4 because they are directly attached. The other
four routes were learned via a routing protocol, which can be RIP, EIGRP, or NLSP. (NLSP is
not covered on the CCNA exam.) Server 1 and Server 2 send RIP updates advertising networks
1000 and 1001, respectively. That is one reason why NetWare servers send RIP updates even if
they have only one interface, as is the case with Server 1.
So, servers' internal network numbers must be in the routing tables of the routers because their
internal addresses are used as the destination address of packets.
Encapsulation is the term used by Cisco to describe the type of data link header built in the
routing algorithm illustrated in Figure 5-33. Encapsulation is also a source of confusion for
many people when considering IPX, particularly when Ethernet is in use. Consider the IPX
packet sent by Client 1 to Server 1 in Figure 5-34. Each successive router discards the data link
header of the incoming frame and builds a new data link header according to the type of
interface. However, Novell supports four different styles of Ethernet header that can be built at
R3. The types of encapsulating Ethernet headers are shown in Figure 5-35 and are listed in
Table 5-32. First, here's a brief summary of encapsulation:
Data link encapsulation defines the details of data link headers and trailers created by a
router and placed around a packet, before completing the routing process by forwarding
the frame out an interface.
Table 5-31
IPX Routing Table, R3
Network
Outgoing Interface
Next Router
1
s0
3.0200.0000.2222
2
s0
3.0200.0000.2222
3
s0
--
4
E0
--
1000
E0
4.0200.AAAA.AAAA
1001
E0
4.0200.BBBB.BBBB
ch05.fm Page 300 Monday, March 20, 2000 5:06 PM