Route

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28 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

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Routing Theory

Introduction


process that a router uses to forward packets toward
the destination network


based upon the destination IP address of a packet


routers must learn the direction to remote networks


dynamic routing


static routing

Routing

Static Route Operation


Network administrator configures the route using a


local interface

or


next
-
hop address

as their gateway


Router installs the route in the routing table


Administrative distance defaults to 0 when using local
interface as gateway


Administrative distance defaults to 1 when using next
hop as gateway


Packets are routed using the static route



Local interface as gatewy

Next Hop address as gateway

Administrative Distance


Optional parameter that gives a measure of
the reliability of the route


Lower value


more reliable route


A value between 0 and 255 is entered after
next hop | outgoing interface if value other
than default is desired

Static routes


Requires network administrator to add and
delete static routes to account for topology
changes


In large network this requires tremendous
amount of administrative time


Often configured in conjunction with
dynamic routing protocol

Default Route


a special static route


used to route packets with destinations that do not
match any of the other routes in the routing table


default route for Internet
-
bound traffic


ip route

0.0.0.0 0.0.0.0 [next
-
hop
-
address |
outgoing interface]

Default Route

Verifying Static Route


show running
-
config is used to view the active
configuration in RAM


show ip route command is used to make sure that
the static route is present in the routing table

Verifying Static Route with show
running
-
config

Verifying Static Route with show
ip route

Routing Protocols


A routing protocol is the communication used
between routers


Routing Information Protocol (RIP)


Interior Gateway Routing Protocol (IGRP)


Enhanced Interior Gateway Routing Protocol (EIGRP)


Open Shortest Path First (OSPF)


A routed protocol is used to direct user traffic


Internet Protocol (IP)


Internetwork Packet Exchange (IPX)


Autonomous systems


collection of networks under a common
administration sharing a common routing strategy


Routing protocols, such as Cisco’s IGRP, require
assignment of a unique, autonomous system
number

Purpose of a routing protocol and
autonomous systems


goal of a routing protocol is to build and maintain
the routing table


it learns all available routes, places the best routes
into the routing table, and removes routes when
they are no longer valid


Whenever the topology of a network changes
because of growth, reconfiguration, or failure, the
network knowledgebase must also change


Autonomous systems (AS) provide the division of
the global internetwork into smaller and more
manageable networks

classes of routing protocols


routing algorithms can be classified into one of two
categories


distance vector


determines the direction (vector) and distance to any link in the
internetwork


link
-
state


recreates the exact topology of the entire internetwork