12'2 Interior and Exterior Routing Protocols

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12.2 Interior and Exterior Routing Protocols
12.2.1 Autonomous system
An autonomous system consists of routers, run by
one or more operators, that present a consistent
view of routing to the external world. The
Network Information Center (NIC) assigns a unique
autonomous system to enterprises. This autonomous
system is a 16 bit number. A routing protocol
such as Cisco's IGRP requires that you specify
this unique, assigned autonomous system number in
your configuration.
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12.2 Interior and Exterior Routing Protocols
12.2.2 Interior versus exterior routing protocols
Exterior routing protocols are used for
communications between autonomous systems.
Interior routing protocols are used within a
single autonomous system.
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12.2 Interior and Exterior Routing Protocols
12.2.3 Interior IP routing protocols

• At the Internet layer of the TCP/IP suite of
  protocols, a router can use an IP routing
  protocol to accomplish routing through the
  implementation of a specific routing algorithm.
  Examples of IP routing protocols include
• RIP -- a distance-vector routing protocol
• IGRP -- Cisco's distance-vector routing protocol
• OSPF -- a link-state routing protocol 
• EIGRP -- a balanced hybrid routing protocol

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12.2 Interior and Exterior Routing Protocols
12.2.4 IP routing configuration tasks
The selection of an IP routing protocol involves
the setting of both global and interface
parameters. Global tasks include selecting a
routing protocol, either RIP or IGRP, and
indicating IP network numbers with specifying
subnet values. The interface task is to assign
network/subnet addresses and the appropriate
subnet mask. Dynamic routing uses broadcasts and
multicasts to communicate with other routers. The
routing metric helps routers find the best path
to each network or subnet.
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12.2 Interior and Exterior Routing Protocols
12.2.5 Using the router and network commands
The router command starts a routing process.
The network command is required because it
enables the routing process to determine which
interfaces will participate in the sending and
receiving of routing updates. The network
numbers must be based on the network class
addresses, not subnet addresses or individual
host addresses. Major network addresses are
limited to Class A, B and C network numbers.
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12.3 RIP 12.3.1 Key elements of RIP

• RIP was originally specified in RFC 1058. Its key
  characteristics include the following
• It is a distance-vector routing protocol.
• Hop count is used as the metric for path
  selection.
• If the hop count is greater than 15, the packet
  will be discarded.
• By default, routing updates are broadcast every
  30 seconds.

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12.3 RIP 12.3.2 Using router rip and network
commands to enable RIP
The router rip command selects RIP as the routing
protocol. The network command assigns a network
class address to which a router will be directly
connected. The routing process associates
interfaces with the network addresses and begins
using RIP on the specified networks. Note In RIP
all subnet masks must be the same. RIP does not
share subnetting information in routing updates.
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12.3 RIP 12.3.4 Monitoring of IP packet flow
using the show ip protocol command
The show ip protocol command displays values,
about routing timers and network information,
that are associated with the entire router. Use
this information to identify a router that you
suspect of delivering bad routing information.
The router in the example sends updated routing
table information every 30 seconds (configured
interval). Seventeen seconds have elapsed since
it sent its last update it will send the next
one in 13 seconds. Following the "Routing for
Networks" line, the router specifies routes for
the listed networks. The last line shows that the
RIP administrative distance is 120
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12.3 RIP 12.3.5 The show ip route command
The show ip route command displays the contents
of the IP routing table, which contains entries
for all known networks and subnetworks, along
with a code that indicates how that information
was learned. Lab Activity  In this lab you will
configure RIP as the routing protocol.
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12.4 I GRP 12.4.1 Key characteristics of IGRP

• IGRP is a distance-vector routing protocol
  developed by Cisco. IGRP sends routing updates at
  90 second intervals, advertising networks for a
  particular autonomous system. Some of the IGRP
  key design characteristics emphasize the
  following
• versatility that enables it to automatically
  handle indefinite, complex topologies
• flexibility for segments that have different
  bandwidth and delay characteristics
• scalability for functioning in very large
  networks
• The IGRP routing protocol by default uses two
  metrics, bandwidth and delay. IGRP can be
  configured to use a combination of variables to
  determine a composite metric. Those variables
  include
• bandwidth
• delay
• load
• reliability

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12.4 IGRP 12.4.2 Using router igrp and network
commands to enable IGRP
The router igrp command selects IGRP as a routing
protocol. The network command specifies any
directly connected networks that are to be
included. Note Like RIP, all subnet masks must
be the same. IGRP does not share subnetting
information in routing updates.
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12.4I GRP 12.4.3 Enabling IGRP on an
IP-addressed network

• IGRP is selected as the routing protocol for
  autonomous system 109. All interfaces connected
  to networks 1.0.0.0 and 2.0.0.0 will be used to
  send and receive IGRP routing updates. In the
  example
• router igrp 109 -- selects IGRP as the routing
  protocol for autonomous system 109
• network 1.0.0.0 -- specifies a directly connected
  network
• network 2.0.0.0 -- specifies a directly connected
  network

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12.4 IGRP 12.4.4 Monitoring IP packet flow using
the show ip protocol command
The show ip protocol command displays parameters,
filters, and network information about all of the
routing protocol(s) (i.e. RIP, IGRP, etc.) in use
on the router. The algorithm used to calculate
the routing metric for IGRP is shown in this
display. It defines the value of the K1-K5
metrics and the maximum hop count. The metric K1
represents bandwidth and the metric K3 represents
delay. By default the values of the metrics K1
and K3 are set to 1. K2,K4 and K5 metric values
are set to 0.
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12.4 IGRP 12.4.5 The show ip interfaces command
The show ip interfaces command displays the
status and global parameters associated with all
IP interfaces. The Cisco IOS software
automatically enters a directly-connected route
in the routing table if the interface is one
through which software can send and receive
packets. Such an interface is marked up. If the
interface is unusable, it is removed from the
routing table. Removing the entry allows the use
of backup routes, if they exist.
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12.4 IGRP 12.4.6 The show ip route command
The show ip route command displays the contents
of an IP routing table. The table contains a list
of all known networks and subnets and the metrics
associated with each entry. Note that in this
example the information was derived from IGRP
(I), or from direct connections (C).
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12.4 IGRP 12.4.7 The debug ip rip command
The debug ip rip command displays RIP routing
updates as they are sent and received. In this
example, the update is sent by 183.8.128.130. It
reported on three routers, one of which is
inaccessible because its hop count is greater
than 15. Updates were then broadcast through
183.8.128.2.  Use caution when using debug
commands. Debug commands are processor intensive
and can decrease network performance or cause
loss of connectivity. Use only during times of
low network usage. Disable the command when
finished by using the command, no debug ip rip or
no debug all.