Giao thức định tuyến - Chapter 3 doc

Dynamic Routing Protocols Functions of Dynamic Routing Protocols: -Dynamically share information between routers.. • However, the expense of using dynamic routing protocols is dedicatin

Trang 2

Describe the role of dynamic routing protocols and esc be e o e o dy a c ou g p o oco s a d

place these protocols in the context of modern network design.

Identify several ways to classify routing protocols

Describe how metrics are used by routing protocols Describe how metrics are used by routing protocols

and identify the metric types used by dynamic routing protocols.

Determine the administrative distance of a route and

describe its importance in the routing process.

Identify the different elements of the routing table

Trang 3

Dynamic Routing Protocols

Dynamic routing protocols are usually y a c ou g p o oco s a e usua y

used in larger networks to ease the

administrative and operational overhead

of using only static routes

Typically, a network uses a combination

Trang 4

The Evolution of Dynamic Routing Protocols

One of the earliest routing protocols was Routing Information Protocol (RIP).

RIP h l d i t i RIP 2 H

– RIP has evolved into a newer version RIPv2 However,

– The newer version of RIP still does not scale to larger network implementations

To address the needs of larger networks, two advanced routing protocols were

developed: Open Shortest Path First (OSPF) and Intermediate

System-to-I t di t S t (IS IS)

Intermediate System (IS-IS).

Cisco developed Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP

(EIGRP), which also scales well in larger network implementations.

Additionally there was the need to interconnect different internetworks and provide

Additionally, there was the need to interconnect different internetworks and provide routing among them Border Gateway Routing (BGP) protocol is now used between ISPs as well as between ISPs and their larger private clients to exchange routing

information.

With the advent of numerous consumer devices using IP the IPv4 addressing space

With the advent of numerous consumer devices using IP, the IPv4 addressing space

is nearly exhausted Thus IPv6 has emerged To support the communication based

on IPv6, newer versions of the IP routing protocols have been developed (see the

IPv6 row in the table).

Trang 5

Function(s) of Dynamic Routing Protocols:

-Dynamically share information between routers.

-Automatically update routing table when topology changes.

-Determine best path to a destination Determine best path to a destination.

– Compared to static routing, dynamic routing protocols require less administrative overhead

• However, the expense of using dynamic routing protocols is dedicating part of a router's However, the expense of using dynamic routing protocols is dedicating part of a router s resources for protocol operation including CPU time and network link bandwidth.

– One of the primary benefits to using a dynamic routing protocol is that routers

exchange routing information whenever there is a topology change This exchange

Trang 6

Despite the benefits of dynamic routing, static routing still esp e e be e s o dy a c ou g, s a c ou g s has its place

There are times when static routing is more appropriate and There are times when static routing is more appropriate and other times when dynamic routing is the better choice

More often than not you will find a combination of both More often than not, you will find a combination of both

types of routing in any network that has a moderate level of complexity

Trang 7

A routing protocol g p

– is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol's choice of best paths g p p

The purpose of a dynamic routing protocol is to:

- Discover remote networks

- Maintaining up-to-date routing information

- Choosing the best path to destination networks Abilit t fi d b t th if th t th i l il bl -Ability to find a new best path if the current path is no longer available

ITE PC v4.0

7

Trang 8

• Algorithm is a finite list of steps used in accomplishing a task

• Algorithms are used for facilitating routing information and best path Algorithms are used for facilitating routing information and best path determination

– Routing protocol messages

• These are messages for discovering neighbors and exchange of routing information , and other tasks to learn and maintain accurate information about the network.

Trang 9

Dynamic Routing Protocol Operation

All routing protocols have the same purpose - to learn about remote networks and to quickly adapt whenever there is a change in the topology

The method that a routing protocol uses to accomplish this depends upon the algorithm it uses and the operational characteristics of that protocol

In general the operations of a dynamic routing protocol can be described as

In general, the operations of a dynamic routing protocol can be described as follows:

– The router sends and receives routing messages on its interfaces.

– The router shares routing messages and routing information with other routers that are using the same routing protocol.

– Routers exchange routing information to learn about remote networks

– When a router detects a topology change the routing protocol can advertise this change to other routers.

ITE PC v4.0

9

Trang 10

Advantages of static routing

Advantages of dynamic routing

-It can backup multiple

interfaces/networks on a router

-Minimal CPU processing

Easier for administrator to

-Administrator has less work maintaining the configuration when adding or deleting networks.

-Easier for administrator to

understand

-Easy to configure

-No extra resources are needed

-Protocols automatically react to the topology changes.

-Configuration is less error-prone.

No extra resources are needed

-More secure

Disadvantages of static routing

g -More scalable, growing the network usually does not present a problem

Disadvantages of dynamic routing

-Network changes require manual

reconfiguration

-Configuration and maintenance is

time-consuming

Disadvantages of dynamic routing

-Router resources are used (CPU cycles, memory and link bandwidth) time consuming

-Does not scale well in large

Trang 11

ITE PC v4.0

11

Trang 12

Classifying Routing Protocols

characteristics Examples include:

-RIP IGRP -IGRP -EIGRP OSPF -OSPF -IS-IS -BGP BGP

a single authority g y

Trang 13

Dynamic routing protocols:

– EIGRP

• The advanced distance vector interior routing protocol developed by Cisco OSPF

Trang 14

An autonomous system (AS) - otherwise known as a

routing domain - is a collection of routers under a

common administration

Because the Internet is based on the ASs concept, two

types of routing protocols are required: interior and

exterior routing protocols

Interior Gateway Protocols (IGP)

- Interior Gateway Protocols (IGP)

• are used for intra-autonomous system routing - routing inside an autonomous system

• IGPs are used for routing within a routing domain, those networks within the control of a single organization g g

– An autonomous system is commonly comprised of many individual networks belonging to companies, schools, and other institutions

• IGPs for IP include RIP, IGRP, EIGRP, OSPF, and IS-IS

Exterior Gateway Protocols (EGP)

- Exterior Gateway Protocols (EGP)

• are used for inter-autonomous system routing - routing between autonomous systems that are under the control

Trang 15

A t t

Autonomous systems

An autonomous system (AS) is a collection of

networks under a common administration

sharing a common routing strategy

To the outside world, an AS is viewed as a single entity The AS may be run by one or more

operators while presenting a consistent view of routing to the external world

The American Registry of Internet Numbers

(ARIN), a service provider, or an administrator

assigns an identifying number to each AS This g y g

autonomous system number is a 16 bit number.

Routing protocols, such as Cisco’s IGRP,

require assignment of a unique, autonomous

Trang 16

http://ws.arin.net/cgi-bin/whois.pl

Trang 17

http://arin.net/education/asn_process/index.html

RFC 1930

AS just like IP, it needs

to apply from ARIN or the appropriate region and be unique on the

internet.

The Internet Assigned Numbers Authority (IANA) has reserved the following block of AS numbers for private use (not to be advertised on the global Internet):

64512 through 65535

ITE PC v4.0

17

Trang 18

IGP: Comparison of Distance Vector & Link

State Routing Protocols

Bellman-– incomplete view of network topology incomplete view of network topology.

• Distance vector protocols use routers as sign posts along the path to the final destination

• Distance vector routing protocols do not have an g p actual map of the network topology

– Generally, periodic updates.

• Some distance vector protocols periodically send complete routing tables to all connected neighbors.

Trang 19

IGP: Comparison of Distance Vector &

Link state

– complete view of network topology is created p p gy

• The sign posts along the way from source to destination are not necessary, because all link- state routers are using an identical "map" of the state routers are using an identical map of the network

– updates are not periodic.

• After the network has converged, a link-state update only sent when there is a change in the topology

ITE PC v4.0

19

Trang 20

Distance vector protocols work

best in situations where:

– The network is simple and flat

Link-state protocols work best in situations where:

– The network design is hierarchical,

p and does not require a special

hierarchical design.

– The administrators do not have

usually occurring in large networks.

– The administrators have a good knowledge of the implemented link- enough knowledge to configure

and troubleshoot link-state

– Specific types of networks, such

as hub-and-spoke networks, are

being implemented.

crucial.

– Worst-case convergence times

in a network are not a concern.

Trang 21

Classful routing protocols

– Do NOT send Do NOT send subnet mask in routing updates subnet mask in routing updates,

– Do NOT support VLSM ,

– Classful routing protocols cannot be used when

a network is subnetted using more than one g

subnet mask,

• Tony: This does not mean you can not subnet the clasasfull network You can still subnet it but can only do it once and all subnet it, but can only do it once and all network needs to have the identical mask

– Routing protocols such as RIPv1 and IGRP

Classless routing protocols g p

– Do send subnet mask in routing updates.

– support variable length subnet masks (VLSM).

• In the figure, the classless version of the network is g , using both /30 and /27 masks in the same topology

• Tony: It means you can create the network with all different sizes of subnets They don’t need to have the same mask.

ITE PC v4.0

21

need to have the same mask

• Classless routing protocols are RIPv2, EIGRP, OSPF, IS-IS, BGP.

Trang 22

Convergence is defined as when all routers’ routing Co e ge ce s de ed as e a ou e s ou g

tables are at a state of consistency

– The network has converged when all routers have complete and

f accurate information about the network

Convergence time is the time it takes routers to share

information, calculate best paths, and update their routing tables.

Routing protocols can be rated based on

the speed to convergence; the faster the

convergence, the better the routing

protocol

– RIP and IGRP are slow to converge

– EIGRP and OSPF are faster to converge EIGRP and OSPF are faster to converge

Trang 23

Routing Protocols Metrics

To select the best path, the routing

protocol must be able to evaluate and

differentiate between the available paths

For this purpose a metric is used.

Metric

– A value used by a routing protocol to determine which routes are better than others.

Each routing protocol uses its own metric

– RIP uses hop count,

• The hop count refers to the number of routers The hop count refers to the number of routers

a packet must cross to reach the destination network

• For R3 in the figure, network 172.16.3.0 is two hops or two routers away

hops, or two routers away

– EIGRP uses a combination of bandwidth and delay,

– OSPF uses bandwidth (cost)

ITE PC v4.0

23

OSPF uses bandwidth (cost)

Trang 24

Metrics used in IP routing protocols

• A simple metric that counts the number of routers

a packet must traverse

Trang 25

The Metric Field in the Routing Table

Metric used for each routing protocol

-RIP - hop count

-IGRP & EIGRP - Bandwidth (used by

default), Delay (used by default), Load ,

Reliability

-IS-IS & OSPF – Cost , Bandwidth

(Cisco’s implementation)

Refer to the example in the figure The Refer to the example in the figure The

routers are using the RIP routing

protocol

– The metric associated with a certain

t b b t i d i th route can be best viewed using the

show ip route command

– The metric value is the second value in

the brackets for a routing table entry

– In the figure, R2 has a route to the

192.168.8.0/24 network that is 2 hops

Trang 26

Load balancing oad ba a c g

– when two or more routes to the same

destination have identical metric values

– This is the ability of a router to

distribute packets among multiple same

cost paths p

Load balancing does not

Load balancing does not automatically means the interfaces

will get use equally

R2 load balances traffic to PC5 over two equal cost paths

??????

Trang 27

Load balancing can be done either oad ba a c g ca be do e e e

per packet or per destination

– How a router actually load balances

packets between the equal-cost paths is

governed by the switching process

R2 load balances traffic to PC5 over two equal cost paths

Example

ITE PC v4.0

27

Trang 28

Router Paths: Equal Cost Load Balancing

To solve this dilemma, a router will use Equal Cost Load

Balancing This means the router sends packets over the multiple

exit interfaces listed in the routing table.

– per-packet load balancing

Trang 29

Load balancing with RIP

*Mar 1 19:10:29.646: IP: tableid=0, s=192.168.14.2 (FastEthernet0/0), d=192.168.16.2 (Serial0/1), routed via RIB

*Mar 1 19:10:29.646: IP: s=192.168.14.2 (FastEthernet0/0), d=192.168.16.2 (Serial0/1), g=192.168.13.2, len 60, forward

*Mar 1 19:10:32.218: IP: s=0.0.0.0 (FastEthernet0/0), d=255.255.255.255, len 604, rcvd 2

*Mar 1 19:10:35.974: IP: s=192.168.13.1 (local), d=255.255.255.255 (Serial0/1), len 72, sending broad/multicast

Định dạng
Số trang	41
Dung lượng	1,76 MB