Network technologies and trends

Feb 19 2009   2:03PM GMT

CCNA, Administrative Distance for the Dynamic Routing Protocols



Posted by: Yasir Irfan
Tags:
640-802 CCNA Exam
Administrative Distance
BGP
CCNA
EIGRP
IGRP
IS-IS
OSPF
RIP
Routing
Routing Protocols

If you are preparing for your CCNA then it’s better to know about the dynamic routing protocols.  Cisco Routers support many dynamic routing protocols for learning routes in a complex network topology. The routing protocols supported are the following:

*       RIP

*       OSPF

*       BGP

*       IS-IS

*       IGRP

*       EIGRP

Each routing protocol has its own Administrative Distance (AD), which is a value representing the trustworthiness of the specific routing protocol. If a router learns a destination route from two or more routing protocols, it selects the route from the protocol having the smallest Administrative Distance.

The below table shows the default Administrative Distance (AD) values for each routing protocol:

Routing Protocol

AD Value

Connected

0

Static

1

eBGP

20

EIGRP

90

IGRP

100

OSPF

110

IS-IS

115

RIP

120

iBGP

200

Now, if the router learns a specific destination route from both OSPF and RIP, it will select the route learned from OSPF because this protocol has a smaller AD compared to RIP (110 instead of 120).

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