Chapter 8: Routing Protocols and Network Address Translation

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CCNA Guide to Cisco Networking

• Chapter 8 Routing Protocols and Network Address
  Translation

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Objectives

• Understand the purpose and operation of network
  address translation (NAT)
• Configure static NAT, dynamic NAT, and dynamic
  NAT with overload
• Understand and configure port address translation
  (PAT)
• Differentiate between nonroutable, routed, and
  routing protocols
• Define Interior Gateway Protocols, Exterior
  Gateway Protocols, distance-vector routing
  protocols, and link-state routing protocols

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Objectives (continued)

• Explain the concepts of count-to-infinity, split
  horizon, split horizon with poison reverse, and
  hold-down timers
• Describe, configure, and monitor the interior
  routing protocols RIP and IGRP
• Explain static routing and administrative
  distance
• Configure static routing and default routes

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Network Address Translation

• Static NAT
• Dynamic NAT
• Port Address Translation
• Dynamic Nat with overload
• Overlapping

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Network Address Translation (continued)
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Network Address Translation (continued)
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Network Address Translation (continued)
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Configuring Network Address Translation

• Configure static NAT
• Define static mapping between the inside address
  and the outside address
• Define the routers interfaces as inside or
  outside
• Basic NAT interface assignment
• RouterA(config) int fa 0/0
• RouterA(config-if) ip nat inside
• RouterA(config-if) int serial 0/1
• RouterA(config-if) ip nat outside

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Configuring Dynamic NAT

• Configure a standard access control list to
  define what internal traffic will be translated
• Define a pool of addresses to be used for dynamic
  NAT allocation
• Link the access list to the NAT pool
• Define interfaces as either inside or outside

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Configuring Dynamic NAT (continued)

• Dynamic NAT router configurations
• RouterA(config) access-list 1 permit 192.168.0.0
  0.0.0.255
• RouterA(config) ip nat pool PoolExample
  209.86.192.200 209.86.192.240 netmask
  255.255.255.0
• RouterA(config) ip nat inside source list 1 pool
  PoolExample
• RouterA(config) int fa 0/0
• RouterA(config-if) ip nat inside
• RouterA(config-if) int serial 0/1
• RouterA(config-if) ip nat outside

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Configuring Port Address Translation To An
Outside Interface

• Configure PAT router commands
• Configure a standard access list to define what
  internal traffic will be translated
• Link the access list to the interface to be used
  for PAT
• Define interfaces as either inside or outside

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Configuring Port Address Translation To An
Outside Interface (continued)

• PAT router commands
• RouterA(config) access-list 1 permit 192.168.0.0
  0.0.0.255
• RouterA(config) ip nat inside source list 1
  interface serial 0/1 overload
• RouterA(config) interface serial 0/1
• RouterA(config-if) ip nat outside
• RouterA(config-if) interface fa 0/0
• RouterA(config-if) ip nat inside

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Configuring Port Address Translation To An
Outside Interface (continued)
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Configuring Dynamic NAT With Overload

• Dynamic NAT with overload is a mixture of dynamic
  NAT and PAT
• Dynamic NAT Pool of inside addresses to a small
  pool of outside addresses
• PAT Same pool of inside addresses to an single
  outside address
• PAT function becomes available when pool of
  outside addresses are all in use
• Use dynamic NAT and PAT configurations using the
  same pool of inside addresses

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Nonroutable Protocols

• Peer-to-peer networks
• Microsoft Windows operation systems
• NetBIOS Enhanced User Interface (NetBEUI)
• Very small
• Fast
• Efficient
• Cannot scale

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Nonroutable Protocols (continued)
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Routed Protocols

• Routed protocols
• Support networks
• Logical addresses
• Transmission Control Protocol/Internet Protocol
  (TCP/IP)
• Internetwork Packet Exchange/Sequence Packet
  Exchange (IPX/SPX)

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Routed Protocols (continued)
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Routing Protocols

• Path determination
• Routing tables
• Metric
• Autonomous system (AS)
• Convergence
• Interior gateway protocols (IGP)
• Routing information protocol (RIP)
• Interior gateway routing protocol (IGRP)
• Enhanced Interior gateway routing protocol
  (EIGRP)
• Open shortest path first (OSPF)
• Exterior gateway protocols (EGP)
• Border gateway protocol (BGP)

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Routing Protocols (continued)
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Routing Protocols (continued)
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Two Types Of IGPs

• Distant vector and link-state
• Distant-vector
• Routing by rumor
• Routing loops
• Count-to-infinity
• Split horizon
• Split horizon with poison reverse
• Hold-down timers

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Two Types Of IGPs (continued)

• Link-state
• Link-state advertisements (LSA)
• Shortest path first (SPF) algorithm
• Link-state packets
• Common view of the topology
• Floods or multicasts LSPs
• Triggered updates

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Two Types Of IGPs (continued)
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Two Types Of IGPs (continued)
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Two Types Of IGPs (continued)
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Two Types Of IGPs (continued)
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Two Types Of IGPs (continued)
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Routing Information Protocol

• RIP has the following attributes
• Distance-vector routing protocol
• Maximum hop count of 15
• 16 hops is considered infinity
• Hop count is the only metric available for path
  selection
• Broadcasts the entire routing table to neighbors
  every 30 seconds
• Capable of load balancing
• Easy to configure

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Enabling RIP Routing
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Enabling RIP Routing (continued)
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Configuring RIP Routing For Each Major Network

• Design the network for the appropriate networks
• Configure interfaces to be gateways for networks
• Configure routing protocol
• In router mode establish networks to be advertised

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Configuring RIP Routing For Each Major Network
(continued)
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Configuring RIP Routing For Each Major Network
(continued)
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show ip protocol and debug ip rip (continued)
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show ip protocol and debug ip rip
(continued)
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show ip route Command
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show ip route Command (continued)
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show ip route Command (continued)
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Interior Gateway Routing Protocol

• Proprietary distance-vector routing protocol
• Supports hop count of 255
• 100 is the default hop count
• Supports up to four equal cost paths
• Routing table updates every 90 seconds

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Interior Gateway Routing Protocol (continued)

• IGRP metrics
• Hops Number of routers between source and
  destination networks
• Load The load on a link in the path
• Bandwidth The speed of the link (default)
• Reliability Measures reliability with a scale of
  0 to 255
• Delay The delay on the medium (default)
• MTU The size of the datagram

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Interior Gateway Routing Protocol (continued)
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Interior Gateway Routing Protocol (continued)
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Interior Gateway Routing Protocol (continued)
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Interior Gateway Routing Protocol (continued)
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Static Routing

• Adding static routes
• Router(config) ip route destination
  network/destination ip address next hop ip
  address/forwarding interface administrative
  distance
• RouterD(config) ip route 172.32.3.0
  255.255.255.0 172.32.2.2
• Changing administrative distance
• Default administrative distance of a static route
  is
• 0 if a forwarding interface is configured
• 1 if a next hop ip address is configured
• Router(config) ip route 192.168.5.0
  255.255.255.0 192.168.4.2. 150

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Static Routing (continued)
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Configuring A Default Route

• Routing protocols do not behave equally with
  default routes
• Router(config) ip route 0.0.0.0 0.0.0.0 next
  hop ip address/forwarding interface
  administrative distance
• Router(config) ip default-network forwarding ip
  address

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Configuring A Default Route (continued)
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Summary

• NAT is a technology that allows organizations to
  map valid external addresses to private or
  unregistered internal addresses
• This allows organizations to maintain a
  separation between the Internet and the intranet
  (internal network) while still providing access
  to the Internet
• Organizations can use NAT to allow many more
  people to access the Internet by sharing one or
  more valid public addresses
• PAT allows an organization to map more than one
  internal private IP address to a public IP address

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Summary (continued)

• Protocols vary in their functions, some protocols
  are designed to be used in small networks without
  the need for Network layer addressing
• These protocols are described as nonroutable
  protocols, the most common nonroutable protocol
  is NetBEUI
• Other protocols were designed with the ability to
  move between multiple networks via Network layer
  addressing
• These protocols are routed protocols, the most
  common routed protocol suite is TCP/IP

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Summary (continued)

• Protocols must be available that can find the
  best path throughout an internetwork and relay
  that information to routers
• Routing protocols serve this function on modern
  networks
• Routing protocols are classed in two major
  groups Interior Gateway Protocols and Exterior
  Gateway Protocols
• Interior Gateway Protocols are routing protocols
  that function within a single autonomous system
• Exterior Gateway Protocols function as routing
  protocols between autonomous systems

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Summary (continued)

• Interior routing protocols are further divided
  into distance-vector and link-state routing
  protocols
• These two types of Interior Gateway Protocols use
  very different methods to determine the best path
  in an internetwork
• Distance-vector protocols periodically broadcast
  entire routing tables to neighbor routers
• Link-state protocols multicast link updates to
  routers in their area upon startup and when
  network topology changes
• Two common distance-vector IGPs are the Routing
  Information Protocol and the Interior Gateway
  Routing Protocol

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Summary (continued)

• RIP is an easy-to-configure routing protocol that
  uses hop count as its sole metric
• RIP has a hop count limit of 15
• RIP uses split horizon, split horizon with poison
  reverse, and hold-down timers to help limit
  routing loops
• RIP can be used on Cisco and non-Cisco routers

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Summary (continued)

• IGRP is also a distance-vector routing protocol
  with maximum hop count of 255
• IGRP is not limited to using hop count as its
  sole metric
• IGRP can also use load, bandwidth, reliability,
  and delay when determining best path
• IGRP uses only bandwidth and delay by default
• IGRP is a Cisco proprietary protocol and can only
  be used on Cisco routers

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Summary (continued)

• Static routes are used to conserve bandwidth and
  lower memory and CPU load on a router while still
  allowing for correct routing table creation
• Static routes give administrators control and
  flexibility in path selection in a network