Routing Protocols and Concepts – Chapter 2 ppt

-By default all serial and Ethernet interfaces are down -To enable an interface use the No Shutdown command •The show ip routecommand is used to display the routing table.. Verifying Eth

Static Routing

Routing Protocols and Concepts – Chapter 2

ƒ Define the general role a router plays in networks e e e ge e a o e a ou e p ays e o s

ƒ Describe the directly connected networks, different

router interfaces router interfaces

table and use the CDP protocol

ƒ Describe static routes with exit interfaces

static routes

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General Role of the Router

ƒ Functions of a Router u c o s o a ou e

Best Path SelectionsForwarding packets to destination

ƒ Routers perform packet forwarding by learning about

remote networks and maintaining routing information g g

– The routers primary forwarding decision is based on Layer 3 information, the destination IP address

– The router's routing table is used to find the best match between the destination IP of a packet and a network address

in the routing table

– The routing table will ultimately determine the exit interface to forward the packet and the router will encapsulate that packet in the appropriated data link frame for that outgoing interface

the appropriated data link frame for that outgoing interface

General Role of the Router

ƒ Introducing the Topology oduc g e opo ogy

– The figure shows the topology used in this chapter

– 3 1800 series routers connected via WAN links

– Each router connected to a LAN represented by a switch and a PC

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General Role of the Router

ƒ Connections of a Router for WAN

-A router has a DB-60 port that can support 5

different cabling standards

– Newer routers support the smart serial pp

interface that allows for more data to be

forwarded across fewer cable pins.

ƒ Connections of a Router for Ethernet

- 2 types of connectors can be used: Straight

through and Cross-over

ƒ Straight through used to connect:

-Switch-to-Router, Switch-to-PC,

Hub-to-PC, Hub-to-Server

ƒ Cross-over used to connect (pin 1 connected Cross-over used to connect (pin 1 connected

to pin 3, and pin 2 connected to pin 6):

-Switch, PC-to-PC, Hub, Hub-to-Hub, Router-to-Router, PC- , , , Router

Switch-to-General Role of the Router in COD

ƒ Smart Serial cables: DCE and DTE S a Se a cab es C a d

-Use straight cable to connect between

ƒ Ethernet cables:

ƒ Cross-over cable: RED cable

ƒ Roll-over cable: flat cables

ƒ Straight cable: all other cables

http://www.csdata.com/csdonline/customer/home.php

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ƒ In our labs we will use serial DTE/DCE cables (no

CSU/DSU) with a DTE cable connected to one router and

a DCE cable connected to the other router.

the interface information on a condensed format

-By default all serial and Ethernet interfaces are down

-To enable an interface use the No Shutdown command

•The show ip routecommand is used to display the routing table

•Initially, the routing table is empty if no interfaces have

the router

Verifying Ethernet interface

description for all interfaces on the routerp

fast Ethernet port

R1#show interfaces fastethernet 0/0

• R1#show interfaces fastethernet 0/0

• FastEthernet0/0 is administratively down, line protocol is down

• Administratively down means that the interface is currently in the shutdown mode, or turned off

• Line protocol is down means in this case that the interface is not receiving a carrier signal from

• Line protocol is down means, in this case, that the interface is not receiving a carrier signal from

a switch or the hub This condition may also be due to the fact that the interface is in shutdown mode

• You will notice that the show interfaces command does not show any IP addresses on R1's interfaces The reason for this is because we have not yet configured IP addresses on any of the interfaces The reason for this is because we have not yet configured IP addresses on any of the interfaces.

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– Show runShow run –

• command displays the current configuration file that the router is using Configuration commands are temporarily stored in the running configuration file and implemented immediately by the router

and implemented immediately by the router

• However, using show running-config is not necessarily the best way to verify interface configurations

-Show ip interface brief –

- can be used to see a portion of the interface information in a condensed format

Configuring an Ethernet interface

By default, all router interfaces are shutdown To enable this

interface, use the no shutdown command, which changes the

interface from administratively down to up

interface from administratively down to up.

R1(config)#interface fastethernet 0/0

R1(config-if)#ip address 172.16.3.1 255.255.255.0

R1(config-if)#no shutdown

The following message is returned from the IOS:

*Mar 1 01:16:08.212: %LINK-3-UPDOWN: Interface

FastEthernet0/0, changed state to up

*Mar 1 01:16:09.214: %LINEPROTO-5-UPDOWN: Line

protocol on Interface FastEthernet0/0, changed state to up

– The first changed state to up message indicates that,

physically, the connection is good If you do not get this first

message, be sure that the interface is properly connected to g , p p y

a carrier signal from switch or a hub

– The second changed state to up message indicates that the

Data Link layer is operational

• However WAN interfaces in a lab environment require

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• However, WAN interfaces in a lab environment require clocking on one side of the link If you do correctly set the clock rate, then line protocol will not change to up.

Configuring an Ethernet interface

ƒ Unsolicited Messages from IOS g

ƒ The IOS often sends unsolicited messages

ƒ As you can see in the figure, sometimes these

messages will occur when you are in the middle

messages will occur when you are in the middle

of typing a command, such as configuring a

description for the interface

–The IOS message does not affect the command,

but it can cause you to lose your place when typing

ƒ In order to keep the unsolicited output separate In order to keep the unsolicited output separate

from your input, enter line configuration mode

for the consoled port and add the logging

synchronous command, as shown You will see

that messages returned by IOS no longer

that messages returned by IOS no longer

interfere with your typing.

ƒ Verifying Ethernet interface

- Show interfaces fastEthernet 0/0

ƒ Reading the Routing Table

– Now look at routing table shown in the figure

Notice R1 now has a " directly connected "

FastEthernet 0/0 interface a new network

– The interface was configured with the

172.16.3.1/24 IP address which makes it a

member of the 172.16.3.0/24 network.

ƒ 172.16.0.0/24 is subnetted, 1 subnets

ƒ C 172.16.3.0 is directly connected, FastEthernet0/0

– The C at the beginning of the route indicates

that this is a directly connected network In other

words, R1 has an interface that belongs to this

network

network.

– The /24 subnet mask for this route is displayed

in the line above the actual route

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ƒ 172.16.0.0/24 is subnetted, 1 subnets

– Having a single route represent an entire

network of host IP addresses makes the

network of host IP addresses makes the

routing table smaller, with fewer routes,

which results in faster routing table

lookups

• It means that this route matches all

• It means that this route matches all packets with a destination address belonging to this network

– The routing table could contain all 254

i di id l h t IP dd f th

individual host IP addresses for the

172.16.3.0/24 network, but that is an

inefficient way of storing addresses.

ƒ Verifying Ethernet interface

show interfaces fastethernet 0/0

show ip interface brief

ƒ The show interfaces fastethernet 0/0 command

in the figure now shows

in the figure now shows

– The interface is up, and the line protocol is up

The no shutdown command changed the

interface from administratively down to up

– Notice that the IP address is now displayed.

ƒ The command show ip interface brief in the

figure shows that the interface is up, and the

line protocol is up (in a condensed format)

ƒ Typically, the router's Ethernet or FastEthernet

interface will be the default gateway IP address

for any devices on that LAN

for any devices on that LAN.

–For example, PC1 would be configured with a

IP address belonging to the 172.16.3.0/24

network, with the default gateway IP address

Ethernet Interfaces Participate in ARP

ƒ A router's Ethernet interface participates

in a LAN network just like any other

device on that network

device on that network.

– This means that these interfaces have a

Layer 2 MAC address, as shown in the figure

The show interfaces command displays the

MAC dd f th Eth t i t f

MAC address for the Ethernet interfaces.

– If a router has a packet destined for a

device on a directly connected Ethernet

network, it checks the ARP table for an entry , y

with that destination IP address in order to

map it to the MAC address.

-Enter interface configuration mode

-Enter in the ip address and subnet maskEnter in the ip address and subnet mask

-Enter in the no shutdown command

– in this case, Serial 0/0/0 However, because both interfaces are members of the same

network, they both must have IP addresses that belong to the 172.16.2.0/24 network.

If we now issue the show interfaces serial 0/0/0 command on either router we still see that

– If we now issue the show interfaces serial 0/0/0 command on either router, we still see that

the link is up/down

ƒ R2#show interfaces serial 0/0/0

ƒ Serial0/0/0 is up, line protocol is down p, p

– The physical link between R1 and R2 is up because both ends of the serial link have been

configured correctly with an IP address/mask and enabled with the no shutdown command

– However, the line protocol is still down This is because the interface is not receiving a clock

signal

– There is still one more command that we need to enter, the clock rate command, on the

router with the DCE cable The clock rate command will set the clock signal for the link

Interfaces Step 1 Step 3

Setup IP but not “no shut” Configured the clock rate

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ƒ Examining Router Interfaces

-Physically connecting a WAN Interface

A WAN Physical Layer connection has sides:

-A WAN Physical Layer connection has sides:

ƒData Circuit-terminating Equipment (DCE) – This is the service provider CSU/DSU is a DCE device

ƒ The CSU/DSU (DCE device) is used to convert the data from the router (DTE device) into a form acceptable to the WAN service provider

ƒ a DCE device such as a CSU/DSU will provide the clock.

ƒData Terminal Equipment (DTE) – Typically the router is the DTE device

Up-to-date technology

Cisco 1-Port T1/Fractional T1

Cisco 1 Port T1/Fractional T1

DSU/CSU WAN Interface Card

(WIC-1DSU-T1-V2=)

- What is the significant of the information 1?

Interfaces

ƒ For serial links that are directly interconnected, as in a

lab environment, one side of a connection must be

considered a DCE and provide a clocking signal

ƒ You can also distinguish DTE from DCE

– 1) by looking at the connector between the two cables

The DTE cable has a male connector whereas the DCE

The DTE cable has a male connector, whereas the DCE

cable has a female connector

– 2) If a cable is connected between the two routers, you

can use the show controllers command to determine

can use the show controllers command to determine

which end of the cable is attached to that interface

R1#show controllers serial 0/0/0 Interface Serial0/0/0

ƒ Once the cable is attached, the clock can now be set with

the clock rate command

the clock rate command

– The available clock rates, in bits per second, are

ƒ 01:10:28: %LINEPROTO-5-UPDOWN: Line protocol on

Interface Serial0/0, changed state to up

ƒ Note: If a router's interface with a DTE cable is configured

ƒ Note: If a router s interface with a DTE cable is configured

with the clock rate command, the IOS will disregard the

command and there will be no ill effects.

–Use the “show controllers serial 0/0/0” to

find out whether it is a DTE or DCE cable

find out whether it is a DTE or DCE cable

Testing Verifying the Serial Interface ConfigurationR1#show interfaces

R1#show ip interface briefR1#ping 172.16.2.2

R1#show ip route

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R ti T bl C t

Routing Table Concepts

ƒ The show ip route command reveals the content of the routing table.

Routing Table Concepts

ƒ Purpose of the debug ip routing command

ƒ Allows you to view changes that the router performs when adding or Allows you to view changes that the router performs when adding or removing routes in real time

1

3

enable debugging with the debug ip routing command

Configuring the IP address and Subnet Mask

disable interfaces with the shutdown command.

g g

4 Check the routing table

2 Check the routing table

5 Disable debug ip routing by using

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5 routing by using either the “undebug

Routing Table and CDP Protocol

ƒ When a router only has its interfaces configured &

no other routing protocols are configured then:

-The routing table contains only the directly connected

configured interfaces are "up" and "up".

Routing Table and CDP Protocol

ƒ When a router only has its interfaces configured, and the

ti t bl t i th di tl t d t k b t

routing table contains the directly connected networks but

no other routes, only devices on those directly connected

networks are reachable

– R1 can communicate with any device on the 172 16 3 0/24 R1 can communicate with any device on the 172.16.3.0/24

and 172.16.2.0/24 networks.

– R2 can communicate with any device on the 172.16.1.0/24,

172.16.2.0/24, and 192.168.1.0/24 networks.

/ – R3 can communicate with any device on the 192.168.1.0/24

and 192.168.2.0/24 networks.

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Routing Table and CDP Protocol

ƒ Checking each route in turn

– The ping command is used to

check end to end connectivity

Routing Table and CDP Protocol

ƒ Purpose of CDP

–Cisco Discovery Protocol (CDP) is a powerful

network monitoring and troubleshooting tool.

• CDP runs at the Data Link layer connecting the physical

di t th l t l (ULP ) media to the upper-layer protocols (ULPs)

• Because CDP operates at the Data Link layer, two or more Cisco network devices, such as routers that support different Network layer protocols (for example, IP and Novell IPX), can y p ( p , ), learn about each other.

– A layer 2 cisco proprietary tool used to gather information

about other directly connected Cisco devices.

• enables you to access a summary of protocol and address information about Cisco devices that are directly connected.

– the types of devices that are connected,

– the interfaces they are connected to, – the interfaces used to make the connections, – the model numbers of the devices.

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– ……

Routing Table and CDP Protocol

devices that share the same network address space

ƒ R1 and R2 are neighbors Both are members of the 172.16.1.0/24 network

ƒ R2 and R3 are also neighbors R2 and R3 are also neighbors because they both share because they both share the 192.168.1.0/24 network

ƒ But R1 and R3 are not neighbors because they do not share any network address space.

ƒ Layer 2 neighbors

ƒ Layer 2 neighbors

ƒ CDP operates at Layer 2 only Therefore, CDP neighbors are Cisco devices that are directly connected physically and share the same data link

» R1 and S1 are CDP neighbors.

» R1 and R2 are CDP neighbors.

» R2 and S2 are CDP neighbors.

R2 d R3 CDP i hb

Notice the difference between Layer 2 and Layer 3 neighbors The switches are not neighbors to the routers at Layer 3, because the switches are operating at Layer 2 only

» R2 and R3 are CDP neighbors.

» R3 and S3 are CDP neighbors.

the switches are operating at Layer 2 only However, the switches are Layer 2 neighbors

to their directly connected routers

Routing Table and CDP Protocol

ƒ CDP is on by default

– CDP exchanges hardware and software

– CDP exchanges hardware and software

device information with its directly connected

CDP neighbors.

ƒ CDP show commands

ƒ Show cdp neighbors command

- Displays the following information:

ƒ Neighbor device ID

ƒ Local interface

ƒ Local interface

ƒ Holdtime value, in seconds

ƒ Neighbor device capability code

ƒ Neighbor hardware platform

ƒ Neighbor remote port ID

ƒ Show cdp neighbors detail command

-It can also reveals the IP address of a neighboring device

– knowing the IP address of the CDP neighbor is often allows you to telnet into that device

• and a lot more