Routing and Routing Protocols

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Routing and Routing Protocols

• PJC CCNA Semester 2 Ver. 3.0
• by
• William Kelly

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Routing Basics

• Routing is the process of forwarding packets from
  a source to a destination based on the
  destination IP address of the packet
• Routing occurs at layer 3 of the OSI model
  (network layer)
• Routes can be entered by the administrator
  (static) or learned from other routers (dynamic)
• The network layer provides a best-effort
  delivery system
• The router uses a routing table to send packets
  from a source to a destination

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How Routers Route Packets

• Consistent end-to-end Network addressing is the
  key to routing
• Broadcasts are minimized and bandwidth is
  conserved

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The 2 Functions of a Router

• Best Path Determination The router determines
  the best path to a destination by examining the
  Network portion of an address and consulting its
  routing tables (a map of the network contained in
  each router)
• Switching A router accepts a packet on one
  interface and forwards it to another interface

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Routed vs. Routing Protocols

• Routed protocols are network protocols that
  provide enough information for a packet to be
  forwarded from one host to another
• Routing protocols allow routers to communicate
  information about network paths and to maintain
  tables

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Routed vs. Routing Protocols

• Routed protocols are network protocols that
  provide enough information for a packet to be
  forwarded from one host to another
• Routed protocols allow routers to communicate
  information about network paths and to maintain
  tables

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Common Routed and Routing Protocols

• Routed Protocols
• IP
• IPX
• Appletalk
• Routing Protocols
• RIP
• IGRP
• OSPF
• EIGRP
• BGP

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Static Routing

• Routing instructions manually entered by an
  administrator
• Routes must be changed manually when the network
  topology changes
• Static routing is labor intensive
• Static routes are used to enhance security and to
  set up routes accessible by only one path

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Network Layer Protocols
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Configuring a Static Route

• Syntax for entering a static route using the
  interface
• Router(config) ip route 192.168.2.0
  255.255.255.0 S1
• Syntax for entering a static route using the
  next hop addressRouter(config) ip route
  192.168.2.0 255.255.255.0 192.168.1.2
• Syntax for entering a default route (sometimes
  called a quad route)
• Router(config) ip route 0.0.0.0 0.0.0.0 S1
• Syntax for entering a quad route with an
  administrative distance
• Router(config) ip route 0.0.0.0 0.0.0.0
  192.168.1.2 4

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Examining Static Route Syntax

• Syntax for entering a static route using the
  interface
• Router(config) ip route 192.168.2.0
  255.255.255.0 S1

Syntax for entering a static route using the
interface Router(config) ip route 192.168.2.0
255.255.255.0 192.168.1.2
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Common Administrative Distances
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Application of Administrative distances in Static
Routes

• When using a next hop address the default
  administrative distance is 1
• When using an outgoing interface the default
  administrative distance is 0

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Dynamic Routing

• Dynamic routing allows routers to automatically
  share routing (topology) information with other
  routers

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Routing Protocols

• RIP distance vector protocol, metric is hop
  count, max hop count is 15, updates every 30
  seconds
• IGRP distance vector protocol, metric is
  bandwidth, delay, load, and reliability, highly
  scalable for large networks, updates every 90
  seconds
• OSPF link state protocol, uses triggered
  updates, VLSM compliant
• EIGRP Cisco proprietary hybrid protocol, VLSM
  compliant
• BGP exterior routing protocol that was designed
  to work between ISPs

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Commonly Used Metrics

• Bandwidth data capacity of a link
• Delay length of time for a packet to travel
  through links
• Load amount of network activity
• Reliability error rate
• Hop Count number of routers a packet must
  traverse
• Ticks each tick is 1/18 of a second
• Cost

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Link State Basics

• Link State Protocols use the Link State Algorithm
  (also called the Dijkstras algorithm)
• Link State Advertisements (LSAs) are transferred
  between routers to provide topology information
• Each router maintains a topology database of LSA
  information
• The Dijkstras algorithm computes the shortest
  paths to different networks
• The routing table is then populated with the best
  paths

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Link State Concerns

• Processor Overhead
• Memory requirements
• Bandwidth consumption The initial discovery
  process is bandwidth intensive thereafter,
  minimal bandwidth is required

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Hybrid Routing Protocols

• Similar to distance vector protocols in that
  metrics are used but the metrics are more
  accurate.
• Similar to Link State protocols in that triggered
  updates are used instead of period updates
• Examples are IS-IS and EIGRP

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Configuring a Router to Use Routing Protocols

• Starting routing
• Router(config) router protocol options
• ex Router(config) router rip
• Entering Networks
• Router(config) network network-number
• ex Router(config) network 192.168.1.0
• Note A separate network line must be used to
  enter every network whose interface will
  participate in the sending and receiving of
  routing updates

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Autonomous Systems

• Interior Gateway Protocols (IGP) were designed to
  be used in a network designed to be administered
  by a single organization
• Exterior Gateway Protocols (EGP) were designed to
  be used between networks that are controlled by
  two organizations. EGPs such as BGP are used
  between ISPs
• Every autonomous system is assigned a 16 bit
  identifying number by the American Registry of
  Internet Numbers (ARIN)