Performing Loopback testing for Fast Ethernet and Gigabit Ethernet Interfaces | Junos OS | Juniper Networks
Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces | Junos OS | Juniper Networks
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ON THIS PAGEChecklist for Using Loopback Testing for Fast Ethernet and
Gigabit Ethernet InterfacesDiagnose a Suspected Hardware Problem with a Fast Ethernet
or Gigabit Ethernet InterfaceCreate a LoopbackVerify That the Fast Ethernet or Gigabit Ethernet Interface
Is UpConfigure a Static Address Resolution Protocol Table EntryClear Fast Ethernet or Gigabit Ethernet Interface StatisticsPing the Fast Ethernet or Gigabit Ethernet InterfaceCheck for Fast Ethernet or Gigabit Ethernet Interface Error
StatisticsDiagnose a Suspected Circuit Problem
Performing Loopback Testing for Fast Ethernet and Gigabit Ethernet
Interfaces
Checklist for Using Loopback Testing for Fast Ethernet and
Gigabit Ethernet Interfaces
Purpose
Action
PurposeTo use loopback testing to isolate Fast Ethernet and
Gigabit Ethernet interface problems.
ActionTable 1 provides links and
commands for using loopback testing for Fast Ethernet and Gigabit
Ethernet interfaces.
Table 1: Checklist
for Using Loopback Testing for Fast Ethernet and Gigabit Ethernet
InterfacesTasks
Command or Action
Diagnose a Suspected Hardware Problem with a Fast
Ethernet or Gigabit Ethernet Interface
Create a Loopback
Create a Physical Loopback for a Fiber-Optic Interface
Connect the transmit port to the receive port.
Create a Loopback Plug for an RJ-45 Ethernet Interface
Cross pin 1 (TX+) and pin 3 (RX+) together, and pin 2
(TX-) and pin 6 (RX-) together.
Configure a Local Loopback
[edit interfaces
interface-name (fastether-options | gigether-options)]
set loopback
show
commit
Verify That the Fast Ethernet or Gigabit Ethernet
Interface Is Up
show interfaces (fe-fpc/pic/port | ge-fpc/pic/port)
Configure a Static Address Resolution Protocol Table
Entry
show interfaces ge-fpc/pic/port [edit interfaces
interface-name unit logical-unit-number family inet address
address]
set arp ip-address mac mac-address show
commit
run show
arp no-resolve
Clear Fast Ethernet or Gigabit Ethernet Interface
Statistics
clear interfaces statistics fe-fpc/pic/port | ge-fpc/pic/port
Ping the Fast Ethernet or Gigabit Ethernet Interface
ping remote-IP-address bypass-routing
interface (fe-fpc/pic/port |
ge-fpc/pic/port
count 100 rapid
Check for Fast Ethernet or Gigabit Ethernet Interface
Error Statistics
show interfaces (fe-fpc/pic/port | ge-fpc/pic/port ) extensive
Diagnose
a Suspected Circuit Problem
Perform Steps 2 through 8 from Diagnose a Suspected Hardware Problem with a Fast
Ethernet or Gigabit Ethernet Interface.
Diagnose a Suspected Hardware Problem with a Fast Ethernet
or Gigabit Ethernet Interface
Problem
Solution
ProblemDescriptionWhen you suspect a hardware problem, take
the following steps to help verify if there is a problem.
SolutionTo diagnose a suspected hardware problem
with the Ethernet interface, follow these steps:
Create a Loopback
Verify That the Fast Ethernet or Gigabit Ethernet
Interface Is Up
Configure a Static Address Resolution Protocol Table
Entry
Clear Fast Ethernet or Gigabit Ethernet Interface
Statistics
Check for Fast Ethernet or Gigabit Ethernet Interface
Error Statistics
Create a Loopback
You can create a physical loopback or configure a local
loopback to help diagnose a suspected hardware problem. Creating a
physical loopback is recommended because it allows you to test and
verify the transmit and receive ports. If a field engineer is not
available to create the physical loopback, you can configure a local
loopback for the interface. The local loopback creates a loopback
internally in the Physical Interface Card (PIC).
Create a Physical Loopback for a Fiber-Optic Interface
Create a Loopback Plug for an RJ-45 Ethernet Interface
Configure a Local Loopback
Create a Physical Loopback for a Fiber-Optic Interface
Action
To create a physical loopback at the port, connect the transmit
port to the receive port using a known good fiber cable.
Note: Make sure you use single-mode fiber for a
single-mode port and multimode fiber for a multimode port.
Meaning
When you create and then test a physical loopback, you are testing
the transmit and receive ports of the PIC. This action is recommended
if a field engineer is available to create the physical loop as it
provides a more complete test of the PIC.
See AlsoPerforming Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces
Create a Loopback Plug for an RJ-45 Ethernet Interface
Action
To create a loopback plug, cross pin 1 (TX+) and pin 3 (RX+) together, and cross pin
2 (TX-) and pin 6 (RX-) together. You need the following equipment to create the
loopback:
A 6-inch long CAT5 cable
An RJ-45 connector
A crimping tool
Figure 1 illustrates how to create a loopback plug for an RJ-45 Ethernet
interface.
Figure 1: RJ-45 Ethernet Loopback Plug
Meaning
When you create and then test a physical loopback, you are testing the RJ-45
interface of the PIC. This action is recommended if a field engineer is available to
create the physical loop as it provides a more complete test of the PIC.
See AlsoPerforming Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces
Configure a Local Loopback
Action
To configure a local loopback without physically connecting
the transmit port to the receive port, follow these steps:
In configuration mode, go to the following hierarchy level:
Configure the local loopback:
Verify the configuration:
For example:
Commit the change:
For example:
When you create a local loopback, you create an internal loop
on the interface being tested. A local loopback loops the traffic
internally on that PIC. A local loopback tests the interconnection
of the PIC but does not test the transmit and receive ports. On an
Ethernet interface, you cannot create a remote loopback, therefore
there is no option to use a local or remote statement.
Simply including the loopback statement at the [edit
interfaces interface-name (fastether-options
| gigether-options] hierarchy level, places the interface into
local loopback mode.
Note: Remember to delete the loopback statement
after completing the test.
See AlsoCreate a Loopback
See AlsoVerify That the Fast Ethernet or Gigabit Ethernet Interface Is Up
Configure a Static Address Resolution Protocol Table Entry
Clear Fast Ethernet or Gigabit Ethernet Interface Statistics
Ping the Fast Ethernet or Gigabit Ethernet Interface
Check for Fast Ethernet or Gigabit Ethernet Interface Error Statistics
Verify That the Fast Ethernet or Gigabit Ethernet Interface
Is Up
Purpose
Action
Meaning
PurposeDisplay the status of the Fast Ethernet or Gigabit
Ethernet interface to provide the information you need to determine whether the physical link is up
or down.
ActionTo verify that the status of the Fast Ethernet or Gigabit
Ethernet interface is up, use the following Junos OS command-line
interface (CLI) operational mode command:
Sample Output
Meaning
The sample output shows that the link is up and there are no
alarms in this loopback configuration. When an internal loopback is
configured, the physical loopback should come up without an alarm.
Sample Output
When you see that the physical link is down, there may be a
problem with the port. The following output is an example of the show
interfaces fe-fpc/pic/port command when the physical link is down:
MeaningThe sample output shows that the physical link is down
and there are active alarms and defects.
Table 2 presents problem
situations and actions for a physical link that is down.
Table 2: Problems
and Solutions for a Physical Link That Is Down Problem
Action
Cable mismatch
Verify that the fiber connection is correct.
Damaged
and/or dirty cable
Verify that the fiber can successfully loop a known good
port of the same type.
Too much or too little optical
attenuation
Verify that the attenuation is correct per the PIC optical
specifications.
The transmit port is not transmitting within the dBm
optical range per the specifications
Verify that the Tx power of the optics is within range
of the PIC optical specification.
Mismatch between the cable type and the port
Verify that a single-mode fiber cable is connected to
a single-mode interface and that a multimode fiber cable is connected
to a multimode interface. (This problem does not always cause the
physical link to go down; errors and dropped packets are sometimes
the result.)
Configure a Static Address Resolution Protocol Table Entry
Purpose
Configure a static Address Resolution Protocol (ARP) entry to
allow a packet to be sent out of a looped Ethernet interface.
Note: Remove the static ARP entry at the end of
the loop test after you have completed the tests and monitored interface
traffic.
Action
To configure a static ARP table entry for a Gigabit Ethernet
interface, follow these steps. You can follow the same procedure to
configure a static ARP entry for a Fast Ethernet interface.
Find the Media Access Control (MAC) address for the Gigabit
Ethernet interface:
user@host> show interfaces ge-fpc/pic/port
In configuration mode, go to the following hierarchy level:
Configure the static ARP entry:
Commit the configuration:
Verify that the static ARP entry is installed:
Meaning
The sample output is for Step 1 through Step 6 and shows that
a static ARP entry was configured on Gigabit Ethernet interface ge-4/0/6.
Clear Fast Ethernet or Gigabit Ethernet Interface Statistics
Purpose
You can reset the Fast Ethernet and Gigabit Ethernet interface
statistics. Resetting the statistics provides a clean start so that
previous input/output errors and packet statistics do not interfere
with the current diagnostics.
Action
To clear all statistics for the interface, use the following
Junos OS CLI operational mode command:
Sample Output
Meaning
This command clears the interface statistics counters
for the Gigabit Ethernet interface only.
Ping the Fast Ethernet or Gigabit Ethernet Interface
Purpose
Action
Meaning
PurposeUse the ping command to verify the loopback connection.
ActionTo send ping packets from the Ethernet interface, use
the following Junos OS CLI operational mode command:
Sample Output
MeaningThe sample output shows that the time to live (TTL)
expired, indicating that the link is receiving the frames from the
ping test. The MAC address used is the same as the physical address
of the port being tested because this allows the port to accept the
frames from the ping test. As the packet is looped over the link,
you expect to receive a TLL exceeded message for each ping sent. These
messages are generated because the ping packets are repeatedly looped
between the router and the physical loopback. When the packet is sent
to the other end of the link, which does not exist, the loopback returns
the packet back to the same interface, where it is again subjected
to the Packet Forwarding Engine fabric for routing. After the route
lookup, the TTL is decremented, and the packet is again sent out of
the looped interface. This process repeats until the packed is either
lost, or the TLL expires with subsequent TTL expired message displayed.
Should any errors occur, the packet is discarded and a time-out error
is displayed, rather than the expected TTL expired message. Note that
the default TTL for ICMP echo packets in Junos OS is 64. This means
a given test packet must be successfully sent and received 63 times
before a TTL expired message can be generated. You can alter the TTL
value to adjust the tolerance for loss, for example, a value of 255
is the most demanding test because now the packet must be sent and
received error free 254 times.
Check for Fast Ethernet or Gigabit Ethernet Interface Error
Statistics
Purpose
Action
Meaning
PurposePersistent interface error statistics indicate that
you need to open a case with the Juniper Networks Technical Assistance
Center (JTAC).
ActionTo check the local interface for error statistics, use
the following Junos OS CLI operational mode command:
Sample Output
MeaningCheck for any error statistics. There should not be
any input or output errors. If there are any persistent input or output
errors, open a case with the Juniper Networks Technical Assistance
Center (JTAC) at [email protected], or at 1-888-314-JTAC
(within the United States) or 1-408-745-9500 (from outside the United
States).
Diagnose a Suspected Circuit Problem
Purpose
Action
PurposeWhen you suspect a circuit problem, it is important
to work with the transport-layer engineer to resolve the problem.
The transport-layer engineer may create a loop to the router from
various points in the network. You can then perform tests to verify
the connection from the router to that loopback in the network.
ActionAfter the transport-layer engineer has created the loop
to the router from the network, you must verify the connection from
the router to the loopback in the network. Follow Step 2 through Step
8 in Diagnose a Suspected Hardware Problem with a Fast
Ethernet or Gigabit Ethernet Interface. Keep in mind that
any problems encountered in the test indicate a problem with the connection
from the router to the loopback in the network.
By performing tests to loopbacks at various points in the network,
you can isolate the source of the problem.
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