Ch10-s-13

flutteringevergreenNetworking and Communications

Oct 29, 2013 (4 years and 14 days ago)

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Chapter Overview



Routing Principles


Building Routing Tables


Routing Protocols

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Key to the network connection info


Contract routing tables dynamically


Costs are CPU time and network traffics



IGP and EGP (Interior/Exterior gateway
protocols)

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Interior Gateway Protocols

(IGP) and
Exterior Gateway Protocols

(EGP)

IGP

EGP

Border Gateway Protocol
(BGP)
.

Routing Basics

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Administrative Distances (AD)

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A number between 0 to 255


0 is the most trusted


255 == no traffic should go there


Entering to routing table if two routers both can reach an IP


Rule #1, go with a lower AD


Rule #2, if the two ADs are the same, do hop count, etc
cost/metrics calculations


If cost/metrics calculations are all the same, do a “Load
Balance” test by sending messages to the two routers

AD numbers

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Three classes of routing protocols


Distance vector


Count the number of routers (hops) between two points


Link State


Router has 3 tables: (1) directly attached neighbors, (2) table used
to determines the topology of the entire internetwork, (3) actual
routing table


It knows more about the network than Distance Vector


It use an algorithm to calculate the
shortest path


Hybrid


Combines the two, Cisco proprietary protocol


No “best” approach

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Dynamic Routing


Distance
-
Vector Routing


Routing by rumor


A router passes COMPLETE routing
-
table to neighboring
routers


The received routing table is combined with a router’s
own routing table without verification


Use hop count to determine routing, then AD, then
“load balancing”


Know the directly connected networks initially


Build the tables afterward


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Example, initial routing tables


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Example, populated


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RIP Characteristics



RIP: the acronym for Routing Information Protocol


Most common interior gateway protocol (IGP) in
the TCP/IP suite


Originally designed for UNIX systems as a daemon
called routed


Eventually ported to other platforms


Standardized in Request for Comments (RFC) 1058


Updated to version 2, published as RFC 2453


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RIP Communications



RIP routers initiate communications when starting
up by broadcasting a request message on all
network interfaces.


All RIP routers receiving the broadcast respond
with reply messages containing their entire
routing table.


The router receiving the replies updates its own
routing table with the information in the reply
messages.


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RIP Version 1 Message Format


Refresh every 30 seconds

3 minutes == out

Not support subnet mask

Max hop count 15


used by small networks only

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RIP Version 2 Message Format


Message are sent using UDP (user Datagram Protocol)

Port 520

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RIP 2

From

http://www.tcpipguide.com/free/t_RIPVersion2RIP2MessageFormatandFeatures
-
3.htm

RIP vs. RIP v2







VLSM = Variable Length Subnet mask


Discontiguous == two connecting subnets come
from different classful network


Such as connecting 172.16.16.1/24 with 10.3.1.1/24

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Discontiguous


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OSPF Protocol



OSPF: the acronym for Open Shortest Path
First (EGP/IGP)


Standardized in RFC 2328


Uses link
-
state routing


Offers several advantages:



Updates routing tables more quickly when
changes occur on the network


Balances the network load by splitting traffic
between routes with equal metrics


Supports authentication of routing protocol
messages


OSPF and RIPs


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How powerful/useful OSPF is


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IPv6 Routing


Cannot broadcast


RIPng <== RIPv2


EIGRPv6


EIGPR


OSPFv3


OSPF

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?
--
cast


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