15.5 Monitoring Interfaces

Now that you have a little information about troubleshooting the chassis and the major hardware components of the router, we want to spend some time talking about how to monitor the proper operational status of the interfaces. There are two categories of interface monitoring and troubleshooting commands: static and real-time .

Note that it is outside the scope of this chapter to list all possible interface-monitoring commands along with their qualifiers, but you can find this information in your JUNOS operational command reference guide or online in the Technical Documentation section of the Juniper Networks Web site at www.juniper.net.

15.5.1 Static Monitoring

Static monitoring of the router interfaces refers to commands that are one-time, or snapshot, commands used to capture a moment in time in the life of the router. Using a static command, you can see ”at that one second ”what has transpired since the last clearing of the counters. You can also check the status of an interface. You must remember, however, that once the response to the command appears on your screen, it is immediately outdated . That does not mean that it is useless information. It simply means that you got a status update.

The static monitoring commands for use on the router interfaces all start with the root command in operation mode: show interfaces . You can optionally add the interface name , as well as the qualifiers detail or extensive . The detail option provides detailed information on each interface. The extensive option provides even more detail about the interfaces. The output for a simple show interfaces interface-name command on an ATM interface is shown below:

 lab@Chicago> show interfaces at-2/1/1  Physical Interface at-2/1/1, Enabled, Physical link is UP  Interface index: 30   SNMP ifIndex: 13   Link-level type: ATM-PVC, MTU: 4482,  Clocking: Internal, SONET mode,  Speed: OC3, Loopback: None, Payload scrambler: Enabled   Device Flags   : Present Running   Link Flags     : None   Input Rate     : 0 bps (0 pps)   Output Rate    : 0 bps (0 pps)  SONET alarms   : None   SONET defects  : None   Logical interface at-2/1/1.0 (Index 11) (SNMP ifIndex 56)   Flags: Point-to-Point  Encapsulation: ATM-SNAP  Input packets: 0  Output packets: 0    VCI: 0.100      Flags: Active      Total down time: 0 sec, Last down: Never 

In this example, you can see that there are no active SONET alarms or defects present. You can also gather some information about the type of encapsulation in use and the I/O rate of the interface. The output of this command will look a little different for each interface type. Refer to your JUNOS operational command reference for details.

Short summary information, with much less detail, can be obtained by adding the terse option to the command as shown below. Notice that you only see the status, protocol type, and the local and remote addresses. If you need to quickly check the status of an interface, this is a good command to use.

 lab@Chicago>  show interfaces terse  Interface      Admin     Link     Proto     Local     Remote at-2/1/1       UP        UP  at-2/1/1.0     UP        UP       inet      10.1.1.1  10.1.1.2  at-2/1/1.100   DOWN      DOWN at-2/1/1.3748  DOWN      DOWN 

To obtain only descriptions of the interfaces, use the descriptions qualifier as shown below. As in the above example, you will see the interface name, followed by its status, and a short description, as manually entered. This can be helpful if you name your interfaces by location or another unique identifier. For instance, in this example, the descriptions seem to identify a location and the PVC in use:

 lab@Chicago>  show interfaces descriptions  Interface      Admin    Link    Description  at-2/1/1.0     UP       UP      Nassau-0  at-2/1/1.100   UP       UP      Nassau-100 at-2/1/1.3748  DOWN     DOWN    Nassau-3748 

Using the show interfaces routing command gives you the routing information for each specific interface. You can also include the optional qualifiers interface-name , brief (default), detail , and summary . Using the interface name, you will view only the information for that particular interface. Using brief, you will get the default display information ”a brief view of the basic information for all interfaces (unless you combine this with the interface name).

  lab@Chicago> show interfaces routing brief  Interface       State     Addresses at-2/1/1.0      Up        ISO         enabled  at-2/1/1.100    Up        INET        10.1.1.1  at-2/1/1.3748   Down      ISO         enabled 

Using detail , you get a more detailed view of each (or a single) interface. The summary option will give you a short summary of the interfaces on the router and their statuses.

  lab@Chicago> show interfaces routing summary  5 physical interfaces (4 up)                3 INET protocol addresses (3 up)  5 ISO protocol addresses (4 up)  0 MPLS protocol addresses (0 up)                0 CCC protocol addresses (0 up) Interface         Index   Metric   Trans.   Status at-2/1/1.0        6       0        0        Broadcast PointToPoint Multicast  at-2/1/1.100      5       0        5        Broadcast PointToPoint Multicast  at-2/1/1.3748     4       0        1        Broadcast PointToPoint Multicast lo0.0             3       0        0        Broadcast PointToPoint Multicast fxp1.0            2       0        0        Broadcast Multicast fxp0.0            1       0        1        Broadcast Multicast 

To gather media-specific information about the interfaces, use the media qualifier. In this example, we are looking at a Fast Ethernet interface. Notice the specific information generated by this command, such as autonegotiation , MAC statistics, and flow control.

  lab@Chicago> show interfaces media  Physical interface: fe-1/0/0, Enabled, Physical link is UP  Interface index: 37,  SNMP ifIndex: 14  Link-level type: Ethernet, MTU: 1514, Source filtering: Disabled  Speed: 100 mbps, Loopback: Disabled,  Flow control: Enabled  Device flags: Present Running  Interface flags: SNMP-Traps  Link flags: None Current address: 00:90:69:0e:0c:69, Hardware address: 00:90:69:0e:0c:69  Input rate: 0 bps (0 pps), Output rate: 0 bps (0 pps)  Active alarms: None  Active defects: None  MAC statistics:   Input octets: 0, Input packets: 0, Output octets: 0, Output packets: 0  Filter statistics:   Filtered packets: 0, Padded packets: 0, Output packet errors: 0  Autonegotiation information:   Negotiated status: Complete, Link partner status: OK   Link partner: Full-duplex, Flow control: None  

For statistical information, the command is show interfaces statistics . The default qualifier is detail . You may also specify a particular interface, as we have in the example below, which shows I/O rates in bits per second, as well as clocking information, and so on:

  lab@Chicago> show interfaces t1-3/1/0 statistics  Physical interface: t1-3/1/0, Enabled, Physical link is Up  Interface index: 129, SNMP ifIndex: 1300  Link-level type: Cisco-HDLC, MTU: 4474, Clocking: Line  Speed: T1, Loopback: Local, FCS: 16, Framing: ESF  Device flags      : Present Running  Interface flags   : Point-to-Point  Link flags        : Keepalives  Statistics last cleared: Never  Input rate     : 0 bps (0 pps), Output rate: 0 bps (0 pps)   Input errors   : 0, Output errors: 0  Active alarms  : None  Active defects     : None  Logical interface t1-3/1/0.0 (Index 4) (SNMP ifIndex 1380)    Flags: Point-to-Point, Encapsulation: Cisco-HDLC    Protocol inet, MTU: 4470      Addresses, Flags: Is-Preferred, Is-Primary        Destination: 10.0.3.2, Local: 10.0.3.1 

Static monitoring using the show interfaces command provides you with a way to get a snapshot of a moment in time of a particular interface. By using different parameters with this command, you can gather a great deal of useful troubleshooting information, such as clocking, encapsulation, interface status, and alarms. The next section takes a look at how you can gather ongoing information about an interface with real-time monitoring.

15.5.2 Real-time Monitoring

Suppose you don't want just a status update. What if you need a running output that is continuously updated? This is when you need real-time monitoring. There are two primary commands that can be used to monitor router interfaces in real-time for immediate feedback: monitor interface and monitor traffic .

The monitor interface command shows statistics for a physical interface updated once per second. You will also see the difference between the statistics at the beginning of the monitoring (or since you last cleared the statistics) and the present update. This is quite helpful when troubleshooting an ongoing problem. Another feature of this command is its ability to discover and display common interface problems like alarms and framing errors. The usage for this command is as follows :

 lab@Chicago> monitor interface <  interface-name  traffic> 

If you do not specify an interface name, you will get output for all interfaces. Adding the traffic qualifier will provide you with traffic data (input and output packets per second, for example) for one or all interfaces.

Table 15-4 lists the key sequences for use with the monitor interface command. These key sequences are not case sensitive.

Table 15-4. Control Keys for the monitor interface Command

Keystroke	Action
C	This key will clear the delta values of the statistics since the last time you cleared them or since the monitor interface command was executed. It will not clear the cumulative statistics on the interface.
F	Use this key to "freeze" the display.
T	Use this key to "thaw" a display that was frozen.
N	The monitor interface command displays interfaces sequentially, in the same order in which they would be displayed by the show interfaces terse command. You can use this key to jump to the next interface in the sequence.
I	This key allows you to specify a given interface to display. Using this key will cause the monitor to prompt you for the name of an interface.
Q	Use this key to quit monitoring.

The monitor traffic command can be compared to the UNIX command tcpdump , which also can be used to display the traffic flowing through an interface. Using the monitor traffic command with Boolean expressions, you can print and examine packet headers on traffic on an interface. The monitor traffic command should be used with caution. If you do not use specific parameters to filter the output, it could impact your router's performance, throughput, or both. If you have any questions about the use of this command, contact JTAC before using it. In addition, you can refer to the Juniper Networks Web site or your copy of the JUNOS documentation for software command reference documents for the version of JUNOS you are using. Search for the section on the traffic match condition. The optional qualifiers that can be used with the monitor traffic command are listed in Table 15-5, along with a short description of each.

Table 15-5. Optional Qualifiers for the monitor traffic Command

Qualifier	Description
absolute-sequence	Prints absolute TCP sequence numbers
brief	The default; displays only the minimal protocol- related information, therefore keeping the tax on the router to a minimum
count	Allows you to specify a finite number of headers to display, which helps keep the capture short and less space- intensive ; ceases output once this limit is reached ”the range is 1 to 1,000,000
detail	Shows some detail ”though not as much as extensive ”such as TTL, from the TCP packet.
extensive	Shows even more detail from TCP packets NOTE For detail and extensive to work with some protocols, you must increase the size option to permit higher output for each packet matched by the monitor traffic command.
interface	Specifies the interface on which to print the packet data; if no interface is specified, the command prints data for the traffic arriving on the lowest numbered interface
layer2-headers	Displays the link-level header for each line NOTE The extensive option will do this for you, as well.
matching	Used when you wish to use regular expression matching to filter the output
no-domain- names	Suppresses the domain portion of hostnames printed
no-resolve	Suppresses printing of symbolic addresses
a no-timestamp	Suppresses the printing of the timestamps
print-ascii	Enables the printing of each packet in ASCII
print-hex	Enables the printing of each packet in hexadecimal format, except for the link-level header
size	Allows the output to receive a certain number of bytes per packet (The default value is 68 bytes and can be increased, if necessary. If the sizing is not adequate, data will be truncated.)