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Chapter 5 IP Routing Routing Protocol

vs.

Routed Protocol

Topics 2

Review

Internetworking

Path determination

Router

IP Address

Routed and Routing Protocols

Network protocols

Routed

Routing

Interior Protocols vs. Exterior Protocols

Routing Protocol Activity

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Review

Router and IP Address

Internetworking 4

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Path determination 5

Path determination is the process that the router uses to choose the next hop in the path for the packet to travel to its destination based on the link bandwidth, hop, delay ...

Router 6

A router is a type of internetworking device that passes data packets between networks, based on Layer 3 addresses.

A router has the ability to make intelligent decisions regarding the best path for delivery of data on the network.

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IP addresses 7

IP addresses are implemented in software, and refer to the network on which a device is located.

IP addressing scheme, according to their geographical location, department, or floor within a building.

Because they are implemented in software, IP addresses are fairly easy to change.

Router and Bridge 8

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Router connections 9

Routers connect two or more networks, each of which must have a unique network number in order for routing to be successful.

The unique network number is incorporated into the IP address that is assigned to each device attached to that network.

Router Interface 10

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Router function 11

Router function (cont.1) 12

Strips off the data link header,

carried by the frame.

(The data link header contains the

MAC addresses of the source and

destination.)

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Router function (cont.2) 13

Examines the network layer

address to determine the

destination network.

Router function (cont.3) 14

Consults its routing tables to

determine which of its interfaces it

will use to send the data, in order

for it to reach its destination

network.

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Router function (cont.4) 15

Send the data out interface B1, the

router would encapsulate the data

in the appropriate data link frame.

Router Interface example 16

Interface is a router’s attachment to a network, it may also be referred to as a port. In IP routing.

Each interface must have a separate, unique network address.

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ROUTED AND ROUTING

PROTOCOLS

Network protocols 18

In order to allow two host communicate together through internetwork, they need a same network protocol.

Protocols are like languages.

IP is a network layer protocol.

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Network protocol operation 19

Routed protocol 20

Protocols that provide support for the network layer are called routed or routable protocols.

IP is a network layer protocol, and because of that, it can be routed over an internetwork.

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Protocol addressing variations 21

Three important routed protocols 22

TCP/IP: 04 bytes Class A: 1 byte network + 3 bytes host

Class B: 2 bytes network + 2 bytes host

Class C: 3 bytes network + 1 byte host

IPX/SPX: 10 bytes 4 bytes network + 6 bytes host

AppleTalk: 03 bytes 2 bytes network + 1 byte host

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Non-routable protocol 23

Non-routable protocols are protocols that do not support Layer 3.

The most common of these non-routable protocols is NetBEUI.

NetBEUI is a small, fast, and efficient protocol that is limited to running on one segment.

Addressing of a routable protocol 24

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Routing table 25

131.108.1.0 E0

131.108.2.0 E1

131.108.3.0 E2

Multi-protocol routing 26

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Classification #1: Static and Dynamic 27

Static routes: The network administrator manually enter the routing

information in the router.

Dynamic routes: Routers can learn the information from each other on the fly.

Using routing protocol to update routing information.

RIP, IGRP, EIGRP, OSPF …

Static routes 28

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Dynamic routes 29

Static vs. dynamic routes 30

Static routes:

For hiding parts of an internetwork.

To test a particular link in a network.

For maintaining routing tables whenever there is only one path to a destination network.

Dynamic routes:

Maintenance of routing table.

Timely distribution of information in the form of routing updates.

Relies on routing protocol to share knowledge.

Routers can adjust to changing network conditions.

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Routing protocol 31

Routing protocols determine the paths that routed protocols follow to their destinations.

Routing protocols enable routers that are connected to create a map, internally, of other routers in the network or on the Internet.

Routed vs. Routing protocol 32

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Classification #2: IGP and EGP 33

Dynamic routes.

Interior Gateway Protocols (RIP, IGRP, EIGRP, OSPF):

Be used within an autonomous system, a network of routers under one administration, like a corporate network, a school district's network, or a government agency's network.

Exterior Gateway Protocols (EGP, BGP):

Be used to route packets between autonomous systems.

IGP vs. EGP 34

IGP

EGP

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Classification #3: DVP and LSP 35

Distance-Vector Protocols (RIP, IGRP): View network topology from neighbor’s perspective.

Add distance vectors from router to router.

Frequent, periodic updates.

Pass copy of routing tables to neighbor routers.

Link State Protocols (OSPF): Gets common view of entire network topology.

Calculates the shortest path to other routers.

Event-triggered updates.

Passes link state routing updates to other routers.

Distance vector routing 36

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Link state routing 37

Part II

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© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—3-39

Distance Vector Routing

Distance Vector Routing Protocols

Routers pass periodic copies of their routing table to neighboring routers and accumulate distance vectors.

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Sources of Information and Discovering Routes

Routers discover the best path to destinations from each neighbor.

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Selecting the Best Route with Metrics

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Maintaining Routing Information

Updates proceed step by step from router to router.

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Inconsistent Routing Entries

Each node maintains the distance from itself to each possible destination network.

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Inconsistent Routing Entries (Cont.)

Slow convergence produces inconsistent routing.

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Inconsistent Routing Entries (Cont.) 47

• Router C concludes that the best path to network 10.4.0.0 is through router B.

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Inconsistent Routing Entries (Cont.) 48

• Router A updates its table to reflect the new but erroneous hop count.

Count to Infinity

The hop count for network 10.4.0.0 counts to infinity.

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Defining a Maximum

A limit is set on the number of hops to prevent infinite loops.

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Routing Loops 51

• Packets for network 10.4.0.0 bounce (loop) between routers B and C.

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Split Horizon

It is never useful to send information about a route back in the direction from which the original information came.

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Route Poisoning

Routers advertise the distance of routes that have gone down to infinity.

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Poison Reverse

Poison reverse overrides split horizon.

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Holddown Timers

The router keeps an entry for the “possibly down state” in the network, allowing time for other routers to recompute for this topology change.

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Triggered Updates

The router sends updates when a change in its routing table occurs.

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Eliminating Routing Loops 57

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Eliminating Routing Loops (Cont.) 58

Eliminating Routing Loops (Cont.) 59

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Eliminating Routing Loops (Cont.) 60

Eliminating Routing Loops (Cont.) 61

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Eliminating Routing Loops (Cont.) 62

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© 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—3-65

Link-State and Balanced

Hybrid Routing

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Link-State Routing Protocols

After initial flood of LSAs, link-state routers pass small event-triggered link-state updates to all other routers.

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Drawbacks to Link-State Routing Protocols 68

• Initial discovery may cause flooding.

• Link-state routing is memory- and processor-intensive.

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How Routing Information Is Maintained 69

Link-State Routing Protocol Algorithms 70

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Link-State Network Hierarchy Example 71

• Minimizes routing table entries

• Localizes impact of a topology change within an area

Advantages and Disadvantages of Link-State Routing

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Comparing Distance Vector and Link-State Routing

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Balanced Hybrid Routing

Shares attributes of both distance vector and link-state routing

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Routing Protocol

RIP 81

Most popular.

Interior Gateway Protocol.

Distance Vector Protocol.

Only metric is number of hops.

Maximum number of hops is 15.

Updates every 30 seconds.

Doesn’t always select fastest path.

Generates lots of network traffic.

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IGRP and EIGRP 82

Cisco proprietary.

Interior Gateway Protocol.

Distance Vector Protocol.

Metric is compose of bandwidth, load, delay and reliability.

Maximum number of hops is 255.

Updates every 90 seconds.

EIGRP is an advanced version of IGRP, that is hybrid routing protocol.

OSPF 83

Open Shortest Path First.

Interior Gateway Protocol.

Link State Protocol.

Metric is compose of cost, speed, traffic, reliability, and security.

Event-triggered updates.

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End Chapter V