Routing and Routed

It is important to distinguish between the datagram and the routing protocol used to determine the path of the datagram.

The distinction is between the routed and the routing protocol.

The routed protocol is the Layer 3 protocol used to transfer data from one end device to another across the network. The routed protocol is the Layer 3 datagram that carries the application data as well as the upper-layer information.

The routing protocol is the protocol used to send updates between the routers about the networks that exist in the organization, thereby allowing the routing process to determine the path of the datagram across the network.

Table 4-2 provides a list of routed protocols and their corresponding interior routing protocols.

Table 4-2 Routing and Routed Protocols

Table 4-2 provides a list of routed protocols and their corresponding interior routing protocols.

Table 4-2 Routing and Routed Protocols

Routed Protocol

Corresponding Interior Routing Protocol1

AppleTalk

RTMP, AURP, EIGRP

IPX

RIP, NLSP, EIGRP

Vines

RTP

DECnet IV

DECnet

IP

RIPvl, RIPv2, OSPF, IS-IS, IGRP, EIGRP

^IGRP and EIGRP are Cisco Systems proprietary routing protocols.

^IGRP and EIGRP are Cisco Systems proprietary routing protocols.

The router will reference the routing table and make a decision about forwarding data packets to the end destination identified in the destination address of the datagram/packet.

Table 4-3 shows the fields that are present in a typical routing table.

Table 4-3 The Routing Table

Table 4-3 shows the fields that are present in a typical routing table.

Table 4-3 The Routing Table

Network

Outgoing Interface

Metric

Next Logical Hop

140.100.100.0 /24

E0

6

131.108.13.15

140.100.110.0 /24

E0

7

131.108.13.15

140.100.120.0 /24

E0

8

131.108.13.15

140.100.130.0 /24

E0

8

131.108.13.15

166.99.0.0 /16

E1

10

131.108.14.11

166.90.0.0 /16

E1

11

131.108.14.11

145.0.88.0 /24

S0

3

131.108.10.9

It is useful to look at each field in the routing table to determine the functionality of the table to the routing process. The next sections cover the following fields of the routing table:

• The Network field

• The Outgoing Interface field

• The Metric field

• The Next Logical Hop field

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