Commands and Applications Used to Correct Problems Occurring at the Physical and Data Link Layers

The CIT course discusses certain commands with regards to correcting physical and data link problems. This section discusses those commands. Neither the CIT course nor this book imply by any means that you can fix all physical and data link layer problems by using these commands. The commands are listed and briefly described in Table 8-2. From there, a more detailed discussion of these controller and interface configuration commands is provided. The last part of this section gives examples on correcting physical or data link layer problems by using Cisco IOS interface configuration commands.

Table 8-2 Commands Used to Correct Physical and Data Link Problems

Command

Description

arp -d ip-address

You use this command on end systems with Microsoft operating systems (Windows) to delete a specific entry or the entire contents of the Address Resolution Protocol (ARP) table.

You can clear the entire content of the ARP cache on a Cisco router by using the clear arp-cache command.

interface

This Cisco IOS command enters interface configuration mode (from global configuration mode). When you are in interface configuration mode, you can enter commands such as encapsulation, ip address, clock rate, speed, duplex, and no shutdown.

no shutdown

This Cisco IOS command activates an interface that is inactive (shut down). You enter this command while in interface configuration mode.

encapsulation

This command configures an encapsulation type on an interface (such as serial). You enter this command while in interface configuration mode. The choice of encapsulation type is interface dependent. For example, you have the hdlc, ppp, frame-relay, and other options on a serial interface, but you don't have those options on an Ethernet interface.

clock rate

This is a Cisco IOS interface configuration command. It configures a clock rate on an interface (serial interface with the DCE end of the cable plugged in it). You enter this command while in interface configuration mode.

continues continues

Table 8-2 Commands Used to Correct Physical and Data Link Problems (Continued)

Command

Description

controller

This command enters controller configuration mode. You enter it while in global configuration mode. Controller configuration mode is usually entered for T1/E1 controllers.

or full-duplex half-duplex

A router interface or a switch port might be capable of operating in half-duplex or in full-duplex. (Some can negotiate it with the connected device on the opposite end of the cable.) This is an interface or a port configuration command, and its exact syntax varies based on the device. Two different versions of this command are presented here.

speed {10 | 100 | auto}

A router interface or a switch port might be capable of operating at a speed of 10 or 100 Mbps. (Some can negotiate it with the connected device on the opposite end of the cable.) This is an interface or a port configuration command.

You enter the controller command, as specified in Table 8-2, while in global configuration mode. Controller configuration mode is usually entered for T1/E1 controllers. For example, to enter the controller configuration mode to configure a T1 or E1 controller on the Cisco MC3810, use the controller global configuration command as follows:

TEST-ROUTER(config)#controller {t1 | e1} number

Note that number is the controller unit number. For Cisco MC3810, enter 0 for the multiflex trunk module (MFT) and 1 for the digital voice module (DVM). Some of the configuration commands for the T1/E1 controllers are presented in Table 8-3. These commands configure the access interface ports that are attached to the T1/E1 controllers.

Table 8-3 Common Commands Used to Correct T1/E1 Controller Problems

T1/E1 Controller Configuration Command

Description

channel-group channel-no timeslots timeslot-list speed {56 | 64}

Configures a list of timeslots for voice channels on the T1 or E1 controller.

channel-no is the ID number to identify the channel group. The valid range is 0 to 31.

timeslot-list is the timeslots (DS0s) to include in this channel group. The valid timeslots are 1 to 24 for T1 and 1 to 15 and 17 to 31 for E1.

Table 8-3 Common Commands Used to Correct T1/E1 Controller Problems (Continued)

T1/E1 Controller Configuration Command

Description

clock source {line | internal}

Configures the clock source for a T1/E1 controller.

line is used so that the controller recovers the external clock from the line and provides the recovered clock to the internal (system) clock generator. The line value is the default clock source for the MFT.

internal is used so that the controller synchronizes itself to the internal (system) clock. The internal value is the default clock source for the DVM.

For E1 lines:

framing {crc4 | no-crc4} [australia]

Sets the frame type for the E1 or T1 data line:

sf—Super frame.

esf—Extended super frame.

crc4—CRC4 frame.

australia—E1 frame type used in Australia.

For T1 lines: linecode {ami | b8zs} For E1 lines: linecode {ami | hdb3}

Sets the line-code type for a T1 or E1 line: ami—Alternate mark inversion (AMI) line-code type. b8zs—B8ZS line-code type.

hdb3—High-density bipolar 3 (HDB3) line-code type.

pri-group [timeslots range]

Specifies ISDN Primary Rate Interface (PRI) on a channelized T1 or E1 controller.

timeslots range—Specifies a single range of values from 1 to 23 for channelized T1 and from 1 to 31 for channelized E1.

You can fix a typical physical or data link layer problem whose remedy is configuration changes from within the interface configuration mode. The commands you can enter while in interface configuration mode are of two classes:

■ Those that can be entered on all kinds of interfaces (serial, Ethernet, and so on), such as the IP command

■ Those that are interface hardware-specific, such as the clock rate command, which is entered on serial interfaces (while the DCE end of the serial cable is connected to it)

Example 8-1 shows a sample of the types of commands that are available from within the interface configuration mode. The example was generated for a serial interface. As mentioned earlier, depending on the type of interface, the types and number of commands available vary.

Example 8-1 Sample Interface (Serial) Configuration Commands (C2600 Software, Version 12.2(2)T)

TEST-ROUTER#configure terminal

Enter configuration commands, one per line. End with CNTL/Z. TEST-ROUTER(config)#interface serial0/0 TEST-ROUTER(config-if)#? Interface configuration commands:

access-expression apollo appletalk arp asp autodetect backup bandwidth bridge-group bsc bstun carrier-delay cdp clns clock custom-queue-list dce-terminal-timing-enable decnet default delay description dialer dialer-group diffserv dlsw down-when-looped dspu dxi encapsulation exit fair-queue frame-relay fras full-duplex h323-gateway half-duplex help hold-queue idle-character ignore ignore-dcd invert

Build a bridge boolean access expression

Apollo interface subcommands

Appletalk interface subcommands

Set arp type (arpa, probe, snap) or timeout

ASP interface subcommands

Autodetect Encapsulations on Serial interface

Modify backup parameters

Set bandwidth informational parameter

Transparent bridging interface parameters

BSC interface subcommands

BSTUN interface subcommands

Specify delay for interface transitions

CDP interface subcommands

CLNS interface subcommands

Configure serial interface clock

Assign a custom queue list to an interface

Enable DCE terminal timing

Interface DECnet config commands

Set a command to its defaults

Specify interface throughput delay

Interface specific description

Dial-on-demand routing (DDR) commands

Assign interface to dialer-list diffserv (Provisioning)

DLSw Interface Subcommands

Force looped serial interface down

Down Stream PU

ATM-DXI configuration commands Set encapsulation type for an interface Exit from interface configuration mode Enable Fair Queuing on an Interface Set frame relay parameters DLC Switch Interface Command Configure full-duplex operational mode Configure H323 Gateway

Configure half-duplex and related commands

Description of the interactive help system

Set hold queue depth

Set idle character type ignore signals ignore dcd

Serial invert modes

Example 8-1 Sample Interface (Serial) Configuration Commands (C2600 Software, Version 12.2(2)T) (Continued)

ip ipv6

ipx isis iso-igrp keepalive lan-name lat llc2

load-interval locaddr-priority logging loopback mac-address map-group max-reserved-bandwidth mop mpls mpoa mtu multilink-group netbios no nrzi-encoding ntp ppp priority-group pulse-time random-detect rate-limit roles sap-priority sdllc serial service-policy shutdown smds smrp sna snapshot snmp source

Interface Internet Protocol config commands IPv6 interface subcommands Novell/IPX interface subcommands IS-IS commands

ISO-IGRP interface subcommands Enable keepalive LAN Name command LAT commands

LLC2 Interface Subcommands

Specify interval for load calculation for an interface

Assign a priority group

Configure logging for interface

Configure internal loopback on an interface

Manually set interface MAC address

Configure static map group

Maximum Reservable Bandwidth on an Interface

DEC MOP server commands

Configure MPLS interface parameters

MPOA interface configuration commands

Set the interface Maximum Transmission Unit (MTU)

Put interface in a multilink bundle

Use a defined NETBIOS access list or enable name-caching

Negate a command or set its defaults

Enable use of NRZI encoding

Configure NTP

Point-to-Point Protocol

Assign a priority group to an interface

Force DTR low during resets

Enable Weighted Random Early Detection (WRED) on an Interface Rate Limit

Specify roles (by entering roles mode) Assign a priority group Configure SDLC to LLC2 translation serial interface commands Configure QoS Service Policy Shutdown the selected interface Modify SMDS parameters

Simple Multicast Routing Protocol interface subcommands

SNA pu configuration

Configure snapshot support on the interface Modify SNMP interface parameters Get config from another source continues

Example 8-1 Sample Interface (Serial) Configuration Commands (C2600 Software, Version 12.2(2)T) (Continued)

stun tag-switching tarp timeout traffic-shape transmit-interface trunk-group tx-ring-limit vines xns

STUN interface subcommands

Tag Switching interface configuration commands TARP interface subcommands Define timeout values for this interface Enable Traffic Shaping on an Interface or Sub-Interface

Assign a transmit interface to a receive-only interface

Configure interface to be in a trunk group Configure PA level transmit ring limit VINES interface subcommands XNS interface subcommands

TEST-ROUTER(config-if)#

The output displayed in Example 8-2 was generated so that you could further explore the encapsulation and the clock rate interface configuration commands. Note that both of these commands are hardware specific, are not available for all types of interfaces, and might not work the same way for all interface types. As you can see in Example 8-2, a serial interface was chosen to generate the output. The encapsulation command, when used on serial interfaces, allows you to set the serial encapsulation type (serial protocol frame type such as ppp and frame-relay). You use the clock rate command on a serial interface when the DCE end of a DCE-DTE cable (such as a V35 DCE-DTE pair) is plugged into it, connecting this interface to another serial interface (usually of another router).

Example 8-2 Configuration Options for Cisco IOS Interface Configuration Commands: clock rate and encapsulation

TEST-ROUTER#configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

TEST-ROUTER(config)#interface serial0/0

TEST-ROUTER(config-if)#clock rate ?

Speed (bits per second)

1200 2400 4800

... (output deleted) 2000000 4000000 8000000

<300-4000000> Choose clockrate from list above

TEST-ROUTER(config-if)#encapsulation ? atm-dxi ATM-DXI encapsulation bstun Block Serial tunneling (BSTUN)

Example 8-2 Configuration Options for Cisco IOS Interface Configuration Commands: clock rate and encapsulation (Continued)

frame-relay Frame Relay networks hdlc Serial HDLC synchronous lapb LAPB (X.25 Level 2)

ppp Point-to-Point protocol sdlc SDLC

sdlc-primary SDLC (primary)

sdlc-secondary SDLC (secondary)

smds Switched Megabit Data Service (SMDS)

stun Serial tunneling (STUN)

x25 X.25

TEST-ROUTER(config-if)#end TEST-ROUTER#

5d04h: %SYS-5-CONFIG_I: Configured from console by console

In the first example on using the commands listed in Table 8-2, assume that you find a problem with an interface (serial0/1) of a router named SanJose (see Figure 8-1).

Figure 8-1 Network Topology Diagram for the HDLC Connection Between the SanJose Router and the SanFran Router

Figure 8-1 Network Topology Diagram for the HDLC Connection Between the SanJose Router and the SanFran Router

After observing the output of the show ip interface brief command, you notice that the serial0/1 interface is administratively down. Therefore, you need to enter a Cisco IOS command to activate the interface Serial0/1. To accomplish this, you enter interface configuration mode and apply the no shutdown command. The console messages report that interface Serial0/1 has gone into active state. Example 8-3 displays the commands entered and the messages indicating that the state of interface serial0/1 has changed to up. To continue with the task at hand, enter the show ip interface brief command on the SanJose router to verify the interface status. The results are shown in the last part of Example 8-3. The line status is up on the SanJose router's serial 0/1 interface.

Example 8-3 Correcting the Inactive Interface on a Router

SanJose#show ip

interface brief

Interface

IP-Address

OK?

Method

Status

Protocol

Ethernet0/0

192.168.22.1

YES

manual

up

up

Serial0/0

unassigned

YES

unset

up

up

Serial0/0.1

192.168.1.18

YES

manual

up

up

Serial0/0.2

192.168.1.21

YES

manual

up

up

Serial0/0.4

150.1.12.1

YES

manual

up

up

Serial0/1

150.1.11.5

YES

manual

administratively down down

Loopback0

192.168.1.2

YES

manual

up

up

SanJose#configure terminal

Enter configuration commands, one per

line.

End with CNTL/Z

SanJose(config)#interface serial0/1

SanJose(config-

if)

#no

shutdown

SanJose(config-

if)

#end

SanJose#

5d06h: %SYS-5-CONFIG_I

: Configured from console by

vty0 (192

168

1.22)

SanJose#

5d06h: %LINK-3-

UPDOWN:

Interface Serial0/1,

changed state to

up

5d06h: %LINEPROTO

5-UPDOWN: Line protocol on Interface Serial0/1

changed state

to up

SanJose#show ip

interface brief

Interface

IP-Address

OK?

Method

Status

Protocol

Ethernet0/0

192.168.22.1

YES

manual

up

up

Serial0/0

unassigned

YES

unset

up

up

Serial0/0.1

192.168.1.18

YES

manual

up

up

Serial0/0.2

192.168.1.21

YES

manual

up

up

Serial0/0.4

150.1.12.1

YES

manual

up

up

Serial0/1

150.1.11.5

YES

manual

up

up

Loopback0

192.168.1.2

YES

manual

up

up

SanJose#

Next, you must check the status of the serial 0 interface on the SanFran router (see Figure 8-1 again), which connects to the SanJose router via a T1 link. Example 8-4 shows the resulting output after the show ip interface brief command was entered on the SanFran router. As a final validation effort, use the ping command to verify connectivity across the link between the SanFran and SanJose routers. The ping test is successful (see the bottom of Example 8-4), which validates physical and data link layers between those routers. You have corrected the problem.

Example 8-4 Verifying the Correct Operation of Physical and Data Link Layers on a Link Between Two Cisco Routers

SanFran#show ip

interface brief

Interface

IP-Address

OK? Method

Status

Protocol

Ethernet0

201.1.2.1

YES manual

up

up

Ethernet1

unassigned

YES unset

administratively down

down

Loopback0

201.1.0.2

YES manual

up

up

Serial0

150.1.11.6

YES manual

up

up

Serial1

unassigned

YES unset

administratively down

down

SanFran#ping

150.1.

11.5

Type escape

sequence to abort.

Sending 5, 100-■ 1 1 1 1

byte

ICMP Echos to

150.1.11.5, timeout is 2 seconds:

Success rate

is

100

percent (5/5),

round-trip min/avg/max = 36/39/52 ms

SanFran#

In this second example on usage of the commands listed in Table 8-2, imagine that you have isolated a problem believed to be an encapsulation mismatch on the serial 0 interface of a router called Orlando currently configured for HDLC encapsulation. You have discovered from the documentation that Orlando is connected to SanJose via a Frame Relay PVC using DLCI 211 (not an HDLC connection), as shown in Figure 8-2, and the service provider uses the ANSI LMI.

Figure 8-2 Network Diagram Displaying the Connection Between Orlando and SanJose

Figure 8-2 Network Diagram Displaying the Connection Between Orlando and SanJose

You can see correction done on the encapsulation type, setting the Frame Relay LMI type, and configuring the point-to-point Frame Relay subinterface with the appropriate DLCI number in Example 8-5. After the corrections are made, the line protocol on the serial 0 interface of the Orlando router goes up for a few seconds but then goes down again shortly after. To confirm the event, type the show ip interface brief command. You see once again that the line protocol on serial 0 is down.

Example 8-5 Correcting the Encapsulation Error on the Serial 0 Interface of Orlando

Orlando#show ip interface serial 0

Serial0 is up, line protocol is down

Internet protocol processing disabled Orlando#configure terminal

Enter configuration commands, one per line. End with CNTL/Z. Orlando(config)#interface Serial0 Orlando(config-if)# encapsulation frame-relay Orlando(config-if)# frame-relay lmi-type ansi

Orlando(config-if)# no shut Orlando(config-if)# exit

Orlando(config)#interface Serial0.1 point-to-point Orlando(config-subif)# description *** Link to SanJose *** Orlando(config-subif)# frame-relay interface-dlci 211 Orlando(config-fr-dlci)# ip address 150.1.12.2 255.255.255.252

Orlando(config-if)# end Orlando#

5d19h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,

changed

state

to

up

5d19h: %SYS-5-CONFIG_I: Configured from console by console

Orlando#

5d19h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,

changed

state

to

down

Orlando#show ip

interface brief

Interface

IP-Address

OK?

Method

Status

Protocol

Ethernet0

201.2.1.1

YES

manual

up

up

Ethernet1

unassigned

YES

unset

administratively

down

down

Loopback0

201.2.0.1

YES

manual

up

up

Serial0

unassigned

YES

unset

up

down

Serial0.1

150.1.12.2

YES

manual

down

down

Serial1

unassigned

YES

unset

administratively

down

down

Orlando#

At this point, you decide to investigate the issue by using the show interface and the show frame-relay lmi commands. The results are shown in Example 8-6. Based on the fact that the outputs of both commands display that Orlando is sending LMIs but it is not receiving LMIs (see the shaded lines in Example 8-6), you suspect that the ANSI LMI type that Orlando is using does not match the LMI type currently used by the service provider's local switch.

Example 8-6 Investigating the State of the Serial 0 (Frame Relay) Interface Using the show interface and show frame-relay lmi Commands

Orlando#show interface serial 0

Serial0 is up, line protocol is down Hardware is HD64570

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usee, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation FRAME-RELAY, loopback not set Keepalive set (10 sec)

LMI enq sent 196, LMI stat recvd 0, LMI upd recvd 0, DTE LMI down LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0 LMI DLCI 0 LMI type is ANSI Annex D frame relay DTE ... (output text deleted)

Orlando#show frame-relay lmi

LMI Statistics for interface Serial0 (Frame Relay DTE) LMI TYPE = ANSI

Invalid Unnumbered info 0 Invalid Prot Disc 0

Invalid dummy Call Ref 0 Invalid Msg Type 0

Invalid Status Message 0 Invalid Lock Shift 0

Invalid Information ID 0 Invalid Report IE Len 0

Invalid Report Request 0 Invalid Keep IE Len 0

Num Status Enq. Sent 200 Num Status msgs Rcvd 0

Num Update Status Rcvd 0 Num Status Timeouts 199 Orlando#

Therefore, you decide to test the validity of the ANSI LMI type by removing the frame-relay lmi-type ansi command and relying on the LMI auto-sensing feature of the Cisco serial interface (available as of IOS version 11.2). Example 8-7 displays removal of the frame-relay lmi-type ansi command, along with the console message indicating that the line protocol on interface serialO has changed state to up.

Example 8-7 Removing the frame-relay lmi-type Command and Relying on the LMI Auto-Sensing Feature of the Cisco Serial Interfaces Configured with the Frame Relay Encapsulation

Orlando#configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Orlando(config)#interface serial 0

Orlando(config-if)#no frame-relay lmi-type ansi

Orlando(config-if)#end

Orlando#

5d21h: %SYS-5-CONFIG_I: Configured from console by console Orlando#

5d21h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed state to up Orlando#show ip interface brief

Interface IP-Address OK? Method Status Protocol

Ethernet0 201.2.1.1 YES manual up up

Ethernet1 unassigned YES unset administratively down down continues

Example 8-7 Removing the frame-relay lmi-type Command and Relying on the LMI Auto-Sensing Feature of the Cisco Serial Interfaces Configured with the Frame Relay Encapsulation (Continued)

Loopback0

201.2.0.1

YES

manual

up

up

Serial0

unassigned

YES

unset

up

up

Serial0.1

150.1.12.2

YES

manual

up

up

Seriall

unassigned

YES

unset

administratively

down down

Orlando#

Although you saw the line protocol going up on the serial 0 interface (and on the point-to-point serial 0.1 interface), you decide to test the link at the network layer by pinging Orlando's counterpart on the Frame Relay connection (that is, SanJose). The results are shown in Example 8-8. The 100 percent success rate of the ping command assures you that the link is in good condition. You have corrected the data link layer problem between Orlando and SanJose by fixing the encapsulation type (switching from HDLC to Frame Relay) and setting the Frame Relay LMI type to be auto-sensed (rather than fixated to ANSI) on Orlando's serial 0 interface. Out of curiosity, you then decide to find out what the LMI type used by the service provider is after all (that is, what your router auto-sensed). After the ping command, you type show interface serial 0 on Orlando and find out that the service provider is now using the Cisco LMI type (see Example 8-8). You need to correct your documentation, and you need to find out why the news about the service provider changing its LMI type was not received and implemented on your side.

Example 8-8 Testing the Frame Relay Link Between Orlando and SanJose Using ping

Orlando#ping 150.1.12.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 150.1.12.1, timeout is 2 !!!!!

seconds:

Success rate is 100 percent (5/5), round-trip min/avg/max

= 60/60/60 ms

Orlando#

Orlando#show interface serial 0

Serial0 is up, line protocol is up

Hardware is HD64570

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usee,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation FRAME-RELAY, loopback not set

Keepalive set (10 sec)

LMI enq sent 839, LMI stat recvd 390, LMI upd recvd 0,

DTE LMI up

LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0

LMI DLCI 1023 LMI type is CISCO frame relay DTE

... (output text deleted)

Orlando#

For the third example on correcting problems at the physical and data link layers, imagine that you are assigned to troubleshoot the connection problem between the Toronto router and the Buffalo6000 switch (see Figure 8-3).

Figure 8-3 Partial Network Diagram Showing the Connection Between the Toronto Router and the Buffalo6000 Switch

Buffalo6000

Fa3/1

Toronto

Your troubleshooting efforts (partially shown in Example 8-9) reveal the following to you:

■ Based on the output of the show interface FastEthernet0 command showing this interface administratively down, you need to enable the interface using the no shut command.

■ After the no shut command, the line protocol stays down showing no carrier, so you conclude that the connection of the cable to the interface is bad, loose, or it needs reseating.

Example 8-9 Initial Corrective Actions on the Toronto Router

Toronto#show interface fa0

FastEthernet0 is administratively down, line protocol is down

Hardware is DEC21140, address is 00e0.1eef.8b40 (bia 00e0.1eef

8b40)

MTU 1500 bytes, BW 100000 Kbit, DLY 100 usee,

reliability 128/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, 100BaseTX/FX

... (output text deleted)

Toronto#configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Toronto(config)#interface fastethernet0

Toronto(config-if)#no shutdown

Toronto(config-if)#end

Toronto#

Toronto#show interface fastethernet0

FastEthernet0 is up, line protocol is down

Hardware is DEC21140, address is 00e0.1eef.8b40 (bia 00e0.1eef

8b40)

MTU 1500 bytes, BW 100000 Kbit, DLY 100 usee,

reliability 128/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

continues

Example 8-9 Initial Corrective Actions on the Toronto Router (Continued)

Full-duplex, 100Mb/s, 100BaseTX/FX ... (output text deleted)

121 packets output, 8578 bytes, 0 underruns(0/116/0) 116 output errors, 116 collisions, 1 interface resets 0 babbles, 0 late collision, 0 deferred 116 lost carrier, 0 no carrier

0 output buffer failures, 0 output buffers swapped out Toronto#

After you reseat the loose cable to the fastethernetO interface on the Toronto router, your colleagues send you e-mails reporting that a message about a duplex mode mismatch is displayed on the Buffalo6000 switch:

%CDP-4-DUPLEXMISMATCH:Full/half-duplex mismatch detected o1

The Cisco Discovery Protocol (CDP) creates this message, not the 802.3 auto-negotiation protocol. CDP can report problems it discovers. A duplex mismatch might or might not result in an error message. Another indication of a duplex mismatch is rapidly increasing frame check sequence (FCS) and alignment errors on the half-duplex side and runts on the full-duplex side of a duplex-mismatching connection. Knowing that the connection between the Toronto router and the Buffalo6000 switch must be at 100 Mbps and full-duplex (according to baseline), you configure the Buffalo6000 switch based on these settings, as shown in Example 8-10. The commands shown in Example 8-10 apply to the following types of switch products: Catalyst 2900XL, 3500XL, 2950, 3550, 2948G-L3, 4908G-L3, Catalyst 4000 running Cisco IOS (Supervisor III), and the Catalyst 6000 running Cisco IOS (Native) software.

Example 8-10 Setting the Speed and Duplex on a Catalyst 6000 Running Native IOS

Buffalo6000#show interface fastEthernet 3/1 status

Port Name Status Vlan Duplex Speed

Type

Fa3/1 notconnected routed a-half a-100

10/100BaseTX

Buffalo6000#

Buffalo6000#configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Buffalo6000(config)#interface fastEthernet3/1

Buffalo6000(config-if)#duplex full

Duplex will not be set until speed is set to non-auto value

Buffalo6000(config-if)#speed 100

Buffalo6000(config-if)#duplex full

Buffalo6000(config-if)#"Z

Buffalo6000#show interfaces fastEthernet 3/1 status

Example 8-10 Setting the Speed and Duplex on a Catalyst 6000 Running Native IOS (Continued)

Port Name

Status

Vlan

Duplex

Speed

Type

Fa3/1

connected

routed

full

100

10/100BaseTX

Buffalo6000#

Finally, you decide to recheck the status of the fastEthernet0 interface on the Toronto router to be confident that the problem is corrected. Example 8-11 displays the results. Note that the line protocol is up, keepalive is set, the interface is operating in full-duplex at 100 Mbps, and there is no lost carrier, late collision, output errors, and so on. This troubleshooting task required corrections done at both the physical and data link layers.

Example 8-11 Showing the Status of the FastEthernet0 Interface on the Toronto Router

Toronto#show interfaces fastethernet 0

FastEthernet0 is up, line protocol is up

Hardware is DEC21140, address is 00e0.1eef.8b40 (bia 00e0.1eef.8b40) MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Full-duplex, 100Mb/s, 100BaseTX/FX ARP type: ARPA, ARP Timeout 04:00:00

. (output text deleted)

21021 packets output, 1387934 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier, 0 PAUSE output 0 output buffer failures, 0 output buffers swapped out

Toronto#

0 0

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