ITEC 275 Computer Networks

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ITEC 275 Computer Networks Switching, Routing,
and WANs

• Week Seven 2017
• Robert DAndrea

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Agenda

• Learning Activities
• Domain Name Server (DNS)
• Summarization
• Root Owner DNS
• Routing tables
• Spanning Tree Protocol
• Rapid Spanning Tree Protocol
• Static versus Dynamic Routing
• Routing Protocols and Characteristics

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DNS Domain Names
4
Interpreting a DNS domain names

• DNS has a method of noting and interpreting the
  fully qualified path to a DNS domain name similar
  to the way full paths to files or directories are
  noted or displayed at a command prompt.
• For example, a directory tree path helps point
  to the exact location of a file stored on your
  computer. For Windows computers, the back slash
  (\) indicates each new directory that leads to
  the exact location of a file. For DNS, the
  equivalent is a period (.) indicating each new
  domain level used in a name.

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Interpreting File Names

• UNIX uses the concept of relative and absolute
  file names. If a file name is preceded by a
  forward slash (e.g. /bin), the name is absolute.
  If the name is without a leading slash, it is
  considered relative to your current working
  directory.
• Example1 Present location is /abc/xyz, I am want
  to remove /abc/xyz/read/hello.txt file.
• Using relative path
• rm read/hello.txt

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Interpreting a DNS domain names

• For DNS, an example of a domain name with
  multiple levels is the following, a fully
  qualified domain name (FQDN)
• host-a.example.microsoft.com.
• Unlike the file name example, a DNS FQDN, when
  read from left to right (/proc/bus/usb), moves
  from its most specific information (the DNS name
  for a computer called "host-a") to its highest or
  most general piece of information (the trailing
  period (.) that indicates the root of the DNS
  name tree). This example shows the four separate
  DNS domain levels that lead away from the
  specific host location of "host-a"

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Interpreting a DNS domain names

• 1. The "example" domain, which corresponds to a
  subdomain where the computer name "host-a" is
  registered for use.
• 2. The "microsoft" domain, which corresponds to
  the parent domain that roots the "example"
  subdomain.
• 3. The "com" domain, which corresponds to the
  top-level domain designated for use by business
  or commercial organizations that roots the
  "microsoft" domain.
• 4. The trailing period (.), which is a standard
  separator character used to qualify the full DNS
  domain name to the root level of the DNS
  namespace tree.

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Root Servers

• When a computer on the Internet needs to resolve
  a domain name, it uses resolver software to do
  the lookup. A resolver breaks the name up into
  its labels from right to left. The first
  component is queried using a root server to
  obtain the responsible authoritative server.
  Queries for each name are performed until a name
  server returns the answer of the original query.

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Interpreting a DNS domain names

• As of 2013, there are 13 root name servers, with
  names in the form letter.root-server.net. This
  does not mean that there are only 13 physical
  servers each site uses redundant computer
  equipment to provide reliable service when
  hardware and software fail.

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Interpreting a DNS domain names

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Route Summarization
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Classful Boundary Summarization
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Routing Tables
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Bridge Protocol Data Unit (BPDU)

• What are BPDUs?
• BPDUs are data messages that are exchanged
  across the switches within an extended LAN that
  uses a spanning tree protocol topology. BPDU
  packets contain information on ports, addresses,
  priorities and costs and ensure that the data
  ends up where it was intended to go. BPDU
  messages are exchanged across bridges to detect
  loops in a network topology. The loops are then
  removed by shutting down selected bridge
  interfaces and placing redundant switch ports in
  a backup, or blocked, state.

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Bridge Protocol Data Unit (BPDU)
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Stateless Auto-configuration
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Stateless Auto-configuration

• Stateless Auto Configuration is an important
  feature offered by the IPv6 protocol. It allows
  the various devices attached to an IPv6 network
  to connect to the Internet using the Stateless
  Auto Configuration without requiring any
  intermediate IP support in the form of a Dynamic
  Host Configuration Protocol (DHCP) server. A DHCP
  server holds a pool of IP addresses that are
  dynamically assigned for a specified amount of
  time to the requesting node in a Local Area
  Network (LAN).

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Stateless Auto-configuration

• Stateless Auto Configuration is a boom for the
  Network Administrators since it has automated the
  IP address configuration of individual network
  devices. Earlier, configuration of the IP
  addresses was a manual process requiring support
  of a DHCP server. However, IPv6 allows the
  network devices to automatically acquire IP
  addresses and also has provision for
  renumbering/reallocation of the IP addresses en
  masse. With a rapid increase in the number of
  network devices connected to the Internet, this
  feature was long overdue. It simplifies the
  process of IP address allocation by doing away
  with the need of DHCP servers and also allows a
  more streamlined assignment of network addresses
  there by facilitating unique identification of
  network devices over the Internet.

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Switching and Routing Choices

• Switching
• Layer 2 transparent bridging (switching)
• Multilayer switching
• Spanning Tree Protocol enhancements
• VLAN technologies
• Routing
• Static or dynamic
• Distance-vector and link-state protocols
• Interior and exterior

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Selection Criteria for Switching and Routing
Protocols

• Network traffic characteristics
• Bandwidth, memory, and CPU usage
• The number of peers supported
• The capability to adapt to changes quickly
• Support for authentication

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Making Decisions

• Goals must be established
• Many options should be explored
• The consequences of the decision should be
  investigated
• Contingency plans should be made
• A decision table can be used. Decision tables are
  composed of rows and columns. Each row
  corresponds to a single rule, with the columns
  defining the conditions and actions of the rules.

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Example Decision Table
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Transparent Bridging (Switching) Tasks

• What is Transparent Bridging?
• A transparent bridge is a common type of bridge
  that observes incoming network traffic to
  identify media access control (MAC) addresses.
  These bridges operate in a way that is
  transparent to all the network's connected hosts.
  A transparent bridge records MAC addresses in a
  table that is much like a routing table and
  evaluates that information whenever a packet is
  routed toward its location. A transparent bridge
  may also combine several different bridges to
  better inspect incoming traffic. Transparent
  bridges are used primarily in Ethernet networks.

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Transparent Bridging (Switching) Tasks

• Example of how transparent bridging works
• Transparent bridges save and maintain the
  source-route addresses of incoming frames by
  listening to all the connected bridges and hosts.
  They use a transparent bridging algorithm to a
  accomplish this. The algorithm has five
  components
• Learning
• Flooding
• Filtering
• Forwarding
• Avoiding loops

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Transparent Bridging (Switching) Tasks

• Example of how transparent bridging works
• Consider three hosts, A, B and C, and a bridge
  with three ports. Host A is connected to Bridge
  Port 1, Host B is connected to Bridge Port 2 and
  Host C is connected to Bridge Port 3. Host A
  sends a frame to the bridge that is addressed to
  Host B. The bridge checks the frame's source
  address and creates an address and port number
  entry for Host A in its forwarding table. The
  bridge then examines the frame's destination
  address, but does not find it in its forwarding
  table. As a result, the bridge sends the frame to
  all the other ports (2 and 3). This is called
  flooding. The frame is then received by Host B
  and Host C, which also check the destination
  address. Host B recognizes a destination address
  match and sends a response to Host A. 

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Transparent Bridging (Switching) Tasks

• Example of how transparent bridging works
• On the return path, the bridge adds an address
  and port number entry for Host B to its
  forwarding table. The bridge already has Host A's
  address in its forwarding table so it forwards
  the response only to Port 1. In this way, none of
  the Port 3 hosts are burdened with response
  requirements. Through this process, two-way
  communication between Host A and Host B is
  facilitated without the need for further flooding.

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Transparent Bridging (Switching) Tasks

• Ethernet switches and bridges use transparent
  bridging.
• A transparent bridge connects one or more LAN
  segments so that end systems on different
  segments can communicate with each other
  transparently. An end system sends a frame to a
  destination without knowing whether the
  destination is local or on the other side of the
  bridge.

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Transparent Bridging (Switching) Tasks

• Forward frames transparently
• Learn which port to use for each MAC address
• Flood frames when the destination unicast address
  hasnt been learned yet
• Filter frames from going out ports that dont
  include the destination address
• Flood broadcasts and multicasts

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STP Definitions

• STP is a bridge protocol that uses the STA
  (Spanning Tree Algorithm) to find redundant links
  dynamically and create a spanning-tree topology
  database. Bridges exchange BPDU (Bridge Protocol
  Data Unit) messages with other bridges to detect
  loops.
• BPDU STP hello packet that is sent out at
  configurable intervals to exchange information
  among bridges in the network.

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Transparent Bridging

• Connectivity to different segments

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Switching Table on a Bridge or Switch
MAC Address
Port
1
08-00-07-06-41-B9
2
00-00-0C-60-7C-01
3
00-80-24-07-8C-02
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Cisco Spanning Tree Protocol Enhancements

• PortFast is a Cisco product feature. It supports
  the concept of a switch edge port.
• UplinkFast and Backbone Fast. UpLinkFast is a
  Cisco product feature that is configured on
  access layer switches. Improves the convergence
  time of STP.
• Unidirectional link detection is a hardware
  failure detection between switches.
• Loop Guard is a Cisco product feature. Supports
  the prevention of loops caused by blocking port
  erroneously moving to the forwarding state.

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Redundant Uplinks
Core Layer
X
Distribution Layer
Switch B
Switch C
X
Primary Uplink
Secondary Uplink
Access Layer
X blocked by STP
Switch A

• If a link fails, how long will STP take to
  recover?
• Use UplinkFast to speed convergence

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Protocols for Transporting VLAN Information

• Inter-Switch Link (ISL)
• Tagging protocol
• Cisco proprietary
• IEEE 802.1Q
• Tagging protocol
• IEEE standard
• VLAN Trunk Protocol (VTP)
• VLAN management protocol is a switch-to-switch
  and switch-to-router configuration.

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Protocols for Transporting VLAN Information

• VLAN Trunk Protocol (VTP)
• The VLAN management protocol exchanges VLAN
  configuration changes as they are made to the
  network. VTP manages additions, deletions, and
  renaming of VLANs on a campus network without
  requiring manual intervention at each switch.

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Selecting Routing Protocols

• They all have the same general goal
• To share network reachability information among
  routers
• They differ in many ways
• Interior versus exterior
• Metrics supported hop count or bandwidth.
• Dynamic versus static and default
• Distance-vector versus link-sate
• Classful versus classless
• Scalability

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Interior Versus Exterior Routing Protocols

• Interior routing protocols are used within an
  autonomous system
• Exterior routing protocols are used between
  autonomous systems

Autonomous system definitions A set of routers
that presents a common routing policy to the
internetwork A network or set of networks that
are under the administrative control of a single
entity
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Routing Protocol Metrics

• A metric is the determining factor used by a
  routing algorithm to decide which route to a
  network is better than another
• Examples of metrics
• Bandwidth - capacity
• Delay - time
• Load - amount of network traffic
• Reliability - error rate
• Hop count - number of routers that a packet must
  travel through before reaching the destination
  network
• Cost - arbitrary value defined by the protocol or
  administrator

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Routing Algorithms

• Static routing
• Calculated before hand, offline
• Default routing
• If I dont recognize the destination, just send
  the packet to Router X
• Ciscos On-Demand Routing
• Routing for stub networks
• Uses Cisco Discovery Protocol (CDP)
• Dynamic routing protocol
• Distance-vector algorithms
• Link-state algorithms

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Routing Algorithms

• Stub network has only one default path to
  non-local hosts and no outside network knowledge.
  Non-local stub network traffic uses a single
  logical path when traveling in and out of the
  network.
• A good example would be an individual or group
  that uses only one router to link to an internet
  service provider (ISP). The individual or group
  are considered stub networks by the ISP.

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Routing Algorithms

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Routing Algorithms

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Routing Algorithms

• The default route is the IP address of the next
  hop when no other routes are known.
• To configure the default route to be
  192.168.1.1
• config ter ip route 0.0.0.0 0.0.0.0 192.168.1.1
• An interface can be used as an alternative to and
  IP address. To use serial0/0 for destinations not
  in the routing table, use
• ip route 0.0.0.0 0.0.0.0 serial 0/0

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Routing Algorithms

• A default route of a computer that is
  participating in computer networking is
  the packet forwarding rule (route) taking effect
  when no other route can be determined for a
  given Internet Protocol (IP) destination address.
  All packets for destinations not established in
  the routing table are sent via the default route.
  This route generally points to another router,
  which treats the packet the same way. If a route
  matches, the packet is forwarded accordingly,
  otherwise the packet is forwarded to the default
  route of that router. The process repeats until a
  packet is delivered to the destination. Each
  router traversal counts as one hop in the
  distance calculation for the transmission path.

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Routing Algorithms

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Routing Algorithms

• Ciscos On- Demand Routing
• The Cisco Discovery Protocol (CDP) is a Cisco
  proprietary protocol that, among other things, is
  used to discover other Cisco devices on either
  broadcast or non-broadcast media. CDP provides
  administrators with information that includes the
  IP address, software version, as well as the
  capabilities of the neighbor device.
• On-Demand Routing (ODR) is an enhancement to
  Cisco Discovery Protocol that advertises the
  connected IP prefix or prefixes of a stub router
  via CDP. ODR also supports VLSM (Variable Length
  Subnet Mask), which means that it can be used in
  just about any network.

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Routing Algorithms

• Ciscos On- Demand Routing
• ODR is a feature that provides IP routing for
  stub sites with minimum overhead. The overhead of
  a general, dynamic routing protocol is avoided
  without incurring the configuration and
  management overhead of static routing.
• A stub router can be thought of as a spoke
  router in a hub-and-spoke network topology where
  the only router to which the spoke is adjacent is
  the hub router. In such a network topology, the
  IP routing information required to represent this
  topology is fairly simple. These stub routers
  commonly have a WAN connection to the hub router,
  and a small number of LAN network segments (stub
  networks) are directly connected to the stub
  router.

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Routing Algorithms

• Ciscos On- Demand Routing (ODR)
• It is important to know that ODR is not a
  routing protocol. Instead, it is simply an
  enhancement/feature to CDP that is used to
  dynamically propagate routing information at
  Layer 2. The primary reasons ODR is often
  incorrectly referred to as a routing protocol is
  because it allows routers to dynamically exchange
  routing information. The second reason is because
  ODR is enabled using the router odr global
  configuration command.

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Routing Algorithms

• ODR (On Demand Routing) allows routing
  information from hub/spoke topology to be
  exchanged with hub and entered into hub routing
  table without running any standard routing
  protocol.
• ODR is designed to be used in a partially meshed
  environment (e.g. Frame Relay networks) where a
  hub router maintains one link each to multiple
  stub routers (spokes routers). Therefore, for any
  spoke to communicate with another spoke, such
  traffic must pass through the hub.
• If each stub network is simply made up of the
  stub router and multiple hosts (much like remote
  location of a corporate organization). There is
  no need to run any routing protocols on the stub
  since all host are connected and the routes can
  be exchanged with hub router using ODR. Hub
  routing will install the routes in
  routing/forwarding tables as connected routes
  with next-hop address of each stub respectively.

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Routing Algorithms

• ODR uses CDP protocol that runs by default on
  all Cisco devices. CDP is used by Cisco devices
  to learn and retrieve basic information about
  their connected neighbors. Therefore, disabling
  CDP on a router will also disable propagation of
  ODR traffic.
• The primary benefit of using ODR is that it is
  not CPU intensive and it consumes very little
  bandwidth. 

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Routing Algorithms
53
Routing Algorithms

• Ciscos On- Demand Routing

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Static Routing Example
172.16.20.1
172.16.40.1
172.16.20.2
172.16.40.2
Router A
Router B
Router C
s0
s0
s0
s1
e0
e0
e0
172.16.10.1
172.16.30.1
172.16.50.1
Host A
Host C
Host B
172.16.10.2
172.16.30.2
172.16.50.2
RouterA(config)ip route 172.16.50.0
255.255.255.0 172.16.20.2 Send packets for
subnet 50 to 172.16.20.2 (Router B)
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Default Routing Example

• Interior Routing Protocols
• RIPv1 classful
• RIPv2 classless
• OSPF Build an entire topology
• ISIS
• IGRP older CISCO protocol
• EIGRP Enhanced Interior CISCO protocol
• Exterior Routing Protocol
• BGP

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Default Routing Example

• Routing Protocols Provide
• Discovery of new networks
• Automatic route updating
• Best path determination
• Failover load balancing
• Eliminates human error

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Default Routing Example

• Distance Vector Routing Protocols
• Neighboring routers communicate with each other
  to keep their routing tables updated. A view of
  the entire network is through all routers
  connected together.
• Link State Routing Protocols
• Share link information (up or down) build a
  routing table based on the topology that has been
  built.

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Default Routing
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Default Routing Example
172.16.20.1
172.16.40.1
172.16.20.2
172.16.40.2
Router A
Router B
Router C
s0
s0
s0
s1
e0
e0
e0
172.16.30.1
172.16.50.1
172.16.10.1
Host A
Host C
Host B
172.16.10.2
172.16.30.2
172.16.50.2
RouterA(config)ip route 0.0.0.0 0.0.0.0
172.16.20.2 If its not local, send it to
172.16.20.2 (Router B)
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Distance-Vector Routing

• Router maintains a routing table that lists known
  networks, direction (vector) to each network, and
  the distance to each network
• Router periodically (every 30 seconds, for
  example) transmits the routing table via a
  broadcast packet that reaches all other routers
  on the local segments
• Routers update their routing table, if necessary,
  based on received broadcasts

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Distance-Vector Routing Tables
Router A
Router B
172.16.0.0
192.168.2.0
Router As Routing Table
Router Bs Routing Table
Network Distance Send To 172.16.0.0
0 Port 1 192.168.2.0 1 Router B
Network Distance Send To 192.168.2.0
0 Port 1 172.16.0.0 1 Router A
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Link-State Routing

• Routers send updates only when theres a change
• Router that detects change creates a link-state
  advertisement (LSA) and sends it to neighbors
• Neighbors propagate the change to their neighbors
• Routers update their topological database if
  necessary

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Distance-Vector Vs. Link-State

• Distance-vector algorithms keep a list of
  networks, with next hop and distance (metric)
  information
• Link-state algorithms keep a database of routers
  and links between them
• Link-state algorithms think of the internetwork
  as a graph instead of a list
• When changes occur, link-state algorithms apply
  Dijkstras shortest-path algorithm to find the
  shortest path between any two nodes

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Link-State Routing Protocol
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Choosing Between Distance-Vector and Link-State

• Choose Distance-Vector
• Simple, flat topology
• Hub-and-spoke topology
• Junior network administrators
• Convergence time not a big concern

• Choose Link-State
• Hierarchical topology
• More senior network administrators
• Fast convergence is critical

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Choosing between Distance Vector and Link State
Protocols

• Distance-Vector
• Routing Information Protocol (RIP) Version 1 and
  2
• Interior Gateway Routing Protocol (IGRP)
• Enhanced IGRP
• Border Gateway Protocol (BGP)

• Link-State
• Open Shortest Path First (OSPF)
• Intermediate System-to-Intermediate System (IS-IS)

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Routing Protocols

• Routers talk to routers on the network, sharing
  information with each other.
• Routed protocol IP
• Routing protocol A protocol used by a router.
• Distance Vector routing protocols include
• RIP, RIPv1, RIPv2, IGRP, and EIGRP
• Routers communicate with neighboring routers.
• Distance Metric

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Routing Protocols

• Link State routing protocols include OSPF and
  ISIS
• Routers communicate with all other routers. They
  exchange link state information to build a
  topology of the entire network.
• What direction of interface are you going out of?
• Link State refers to the interface connections or
  links to other routers and networks.

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Routing Protocols

• What is convergence?
• Convergence is when all routers in the network
  have the same picture of the network.

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Routing Information Protocol (RIP)

• First standard routing protocol developed for
  TCP/IP environments
• RIP Version 1 is documented in RFC 1058 (1988)
• RIP Version 2 is documented in RFC 2453 (1998)
• Easy to configure and troubleshoot
• Broadcasts its routing table every 30 seconds 25
  routes per packet
• Uses a single routing metric (hop count) to
  measure the distance to a destination network
  max hop count is 15

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RIP V2 Features

• Includes the subnet mask with route updates
• Supports prefix routing (classless routing, super
  netting)
• Supports variable-length subnet masking (VLSM)
• Includes simple authentication to foil crackers
  from sending routing updates.

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IGRP Solved Problems with RIP

• 15-hop limitation in RIP
• IGRP supports 255 hops
• Reliance on just one metric (hop count)
• IGRP uses bandwidth, delay, reliability, load
• (By default just uses bandwidth and delay)
• RIP's 30-second update timer
• IGRP uses 90 seconds

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EIGRP

• Adjusts to changes in internetwork very quickly
• Incremental updates contain only changes, not
  full routing table
• Updates are delivered reliably
• Router keeps track of neighbors routing tables
  and uses them as feasible successor
• Same metric as IGRP, but more granularity (32
  bits instead of 24 bits)

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Open Shortest Path First (OSPF)

• Open standard, defined in RFC 2328
• Adjusts to changes quickly
• Supports very large internetworks
• Does not use a lot of bandwidth
• Authenticates protocol exchanges to meet security
  goals
• Is an IP routing protocol that is completely link
  state.

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OSPF Metric

• A single dimensionless value called cost. A
  network administrator assigns an OSPF cost to
  each router interface on the path to a network.
  The lower the cost, the more likely the interface
  is to be used to forward data traffic.
• On a Cisco router, the cost of an interface
  defaults to 100,000,000 divided by the bandwidth
  for the interface. For example, a 100-Mbps
  Ethernet interface has a cost of 1.

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OSPF Areas Connected via Area Border Routers
(ABRs)
Area 0 (Backbone)
ABR
ABR
ABR
Area 1
Area 3
Area 2
77
IS-IS

• Intermediate System-to-Intermediate System.
• Link-state routing protocol.
• Designed by the ISO for the OSI protocols.
• Integrated IS-IS handles IP also.

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IS-IS

• The IS-IS routing protocol is a link state
  protocol for interior routing. It is an ISO
  standard and is completely defined in
  ISO/IEC-10589. The ES-IS neighbor greeting
  protocol is used in conjunction with IS-IS.  For
  its hierarchical routing, IS-IS divides the
  network into non-overlapping IS-IS areas and its
  routers are categorized as Level 1 or Level 2
  routers, or both. Level 1 routers are responsible
  for routing packets between LANs within an IS-IS
  area, and Level 2 routers forward packets between
  IS-IS areas. 

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80
IS-IS

•   IS-IS is a routing protocol designed to move
  information efficiently within a computer
  network, a group of physically connected
  computers or similar devices. It accomplishes
  this by determining the best route for datagrams
  through a packet-switched network. The protocol
  was defined as an international standard within
  the Open Systems Interconnections (OSI) reference
  design

81
Border Gateway Protocol (BGP)

• Allows routers in different autonomous systems to
  exchange routing information
• Exterior routing protocol
• Used on the Internet among large ISPs and major
  companies
• Supports route aggregation
• Main metric is the length of the list of
  autonomous system numbers, but BGP also supports
  routing based on policies

82
Border Gateway Protocol (BGP)
83
Internet Protocol (EGP)

• During the early days of the Internet, an
  EGPversion 3 (EGP3) was used to
  interconnect Autonomous Systems.
  Currently, BGP version 4 is the accepted
  standard for Internet routing and has essentially
  replaced the more limited EGP3.

84
Internet Control Message Protocol (ICMP)

• ICMP works at the Network layer and is used by
  IP for many different services. ICMP is a
  management protocol and messaging service for IP.
  Its messages are carried as IP datagrams.

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Routing Protocols Summary

• Distant vector
• RIP and IGRP
• Link-state
• OSPF
• Hybrid
• EIGRP

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Summary

• The selection of switching and routing protocols
  should be based on an analysis of
• Goals
• Scalability and performance characteristics of
  the protocols
• Transparent bridging is used on modern switches
• But other choices involve enhancements to STP and
  protocols for transporting VLAN information
• There are many types of routing protocols and
  many choices within each type

87
Review Questions

• What are some options for enhancing the Spanning
  Tree Protocol?
• What factors will help you decide whether
  distance-vector or link-state routing is best for
  your design customer?
• What factors will help you select a specific
  routing protocol?
• Why do static and default routing still play a
  role in many modern network designs?

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This Weeks Outcomes

• Spanning Tree Protocol
• Rapid Spanning Tree Protocol
• Static versus Dynamic Routing
• Routing Protocols and Characteristics

89
Due this week

• 6-1 Concept questions 5

90
Q A

• Questions, comments, concerns?