(This is also known as routing by rumor.)
Figure 3-5 Distance Vector Protocols
Table 3-1 Default Administrative Distance Values
Route Source Default Distance
Connected network 0
Static route 1
EIGRP 90
OSPF 110
RIPv2 120
External EIGRP 170
Unknown or unbelievable 255 (will not be added to the routing table to pass traf?¬?c)
D B C A
B
D
C A
Routing
Table
Distance = How far?
Vector = In which direction.
Routing
Table
Routing
Table
Routing
Table
104 Chapter 3: Medium-Sized Routed Network Construction
In this way, the algorithm accumulates network distances so that it can maintain a database of
internetwork topology information. Distance vector algorithms do not allow a router to know the
exact topology of an internetwork.
Route Discovery, Selection, and Maintenance
In Figure 3-6, the interface to each directly connected network is shown as having a distance of 0.
Figure 3-6 Routing Information Sources
As the distance vector network discovery process proceeds, routers discover the best path to
nondirectly connected destination networks based on accumulated metrics from each neighbor.
For example, Router A learns about other networks based on information it receives from Router
B.
Pages:
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173