The DIGITAL VNswitch provides two methods for monitoring network activity:
Mirror interface - This feature allows you to diagnose network activity by sampling incoming and outgoing packets from a specified VNswitch interface.
RMON agent - This feature allows you to configure the VNswitch so that it independently monitors its own MIB variables and network traffic.
The VNswitch 900 mirror feature lets you diagnose network activity by sampling incoming and outgoing packets from a specified VNswitch interface. Packets received or transmitted on specified interfaces can be copied to the mirror destination.
The mirror destination interface is a dedicated interface that accepts only mirrored packets. These mirrored packets are derived from specific VNswitch Ethernet-like interfaces and can be forwarded to any destination interface on the VNswitch with an Ethernet interface. By attaching an external network analyzer to the destination interface, you can evaluate packets and troubleshoot the network.
The following restrictions apply to the mirror feature:
Routing must be disabled on VLANs containing interfaces that are mirrored.
All mirror interfaces must be Ethernet-like interfaces (LAN Bridge Tunnels, LANEs, 10 Mb/s Ethernet, 100 Mb/s Ethernet).
Destination interfaces must be dedicated to mirroring.
Ethernet mirror interfaces cannot be configured simultaneously as a receive/transmit interface and a destination interface.
Packets filtered by hardware, a runt packet for example, are not copied to the destination interface.
The mirroring interfaces must reside in a VLAN containing only
Ethernet-like ports, including: 10 Mb/s Ethernet, 100 Mb/s Fast Ethernet, Ethernet Bridge
Tunnels, LAN Emulation (LANE).
For example, a VNswitch 900EF installed in a hub with the VNbus contains 12 Ethernet ports
and one FDDI port. When powered up, the VNswitch 900EF defaults all ports including the
FDDI port to one VLAN. For the mirror to operate in the default VLAN, the FDDI port must
be removed and assigned to another VLAN.
Mirroring does not adversely affect the performance of the VNswitch. If more packets are sent to the destination than can be handled, the packets are dropped. Although the packets will not be available for viewing, operation of the VNswitch is unaffected.
You can access the mirror feature either at the Configuration prompt (Config>), or the Monitor prompt (Monitor>). To access the mirror feature from the Config> prompt, perform the following steps:
Step | Action |
1 |
To access the mirror prompt, at the Config> prompt, enter mirror. |
2 |
Press Return. The Mirror prompt (Mirror Config>) is displayed. |
Before the destination interface is activated, bridging on the specified destination interface must be disabled. If you try to enable a mirror destination while bridging for the destination interface is active, you are prompted with the following message:
The interface that you are setting as the mirror destination is currently functioning as an active bridge port. It is a requirement of the mirror functionality that bridging is disabled. Would you like to proceed? If you proceed, bridging will be disabled on this port and it will be set as the mirror destination.
Once bridging is disabled on the destination interface and mirroring is enabled and you attempt to enable bridging on the destination interface, you are prompted with the following message:
The interface that you are attempting to enable is currently set up as the destination mirror, to proceed, this interface must be disabled as the destination mirror. Would you like to proceed? If you answer yes, bridging will be enabled and this interface will no longer be the mirror destination.
Interaction with SNMP
You cannot activate a mirror destination port and have the
bridge port enabled simultaneously. Therefore, if a port is configured as the mirror
destination and someone attempts to use SNMP to enable the bridge port (for example, by
setting the dot1dStpPortEnable.X bit) the SNMP set will fail. The only way to reconfigure
the mirror port destination is through the local CLI of the VNswitch.
Enabling Bridging After Using the Mirror
Interface
Disabling the mirror destination does not automatically re-enabling bridging. To re-enable
bridging on the destination interface, use the BRIDGE config> set port command.
However, when the mirror destination is disabled, the you are prompted to determine if
bridging should be enabled. If you answer YES, bridging is re-enabled. When you disable
the destination port, you are prompted with the following message: Bridging is currently
disabled on interface n. Do you want to enable bridging?
You can configure the mirror interface to mirror the following types of packets:
Receive packets
Transmit packets
Both receive and transmit packets
None
In addition to setting a mirror interface, you must also set a mirror destination interface using the enable command. Only one destination interface per VNswitch module is allowed.
The steps in the following example set a mirror interface to mirror the packets received and transmitted on Ethernet interface 2, and sets the destination interface to 5:
Step | Action |
1 |
At the Mirror Config> prompt, enter set both 2. |
2 |
Press Return. A mirror interface on interface 2 is set to transmit and receive. |
3 |
To set a mirror destination, at the Mirror Config> prompt, enter enable 5 |
4 |
Press Return. A mirror destination is set on interface 5. |
With the mirror feature, you can simultaneously set multiple interfaces with the set command. For example, you can set all 12 Ethernet ports on the VNswitch 900EX to a mirror interface with one command.
The steps in the following example set mirror interfaces to transmit on Ethernet interfaces 1 through 5, 7 through 12, and enables the destination interface 6:
Step | Action |
1 |
At the Mirror Config> prompt, enter set transmit 1-5, 7-12. Press Return. |
2 |
At the Mirror Config> prompt, enter enable 6. Press Return. A mirror destination is set on interface 6. |
In the example above, Ethernet interfaces 1 through 5 and 7 through 12 are set to mirror transmit packets, and the destination is enabled for Ethernet interface 6. The steps in the following example change the destination from interface 6 to interface 3, and mirrors traffic transmitted on interface 6:
Step | Action |
1 |
At the Mirror Config> prompt, enter set neither 3. Press Return. |
2 |
At the Mirror Config> prompt, enter set transmit 6. Press Return. |
3 |
At the Mirror
Config> prompt, enter enable 3. Press Return. |
You can display all the receive and transmit mirror interfaces, and the destination interface using the list command. To list all the mirror interfaces, perform the following steps:
Step | Action |
1 |
At the Mirror Config> prompt, enter list. |
2 |
Press Return. All mirror interfaces are displayed. |
You can clear all the mirror interfaces and the destination interface with the clear command. To clear all the mirror interfaces, perform the following steps:
Step | Action |
1 |
At the Mirror Config> prompt, enter clear. |
2 |
Press Return. All mirror interfaces and the destination port are cleared. |
You can also clear specific mirror interfaces using the set command. To clear specific mirror interfaces, perform the following steps:
Step | Action |
1 |
At the Mirror Config> prompt, enter set neither 3,4 |
2 |
Press Return. Packets on mirror interfaces 3 and 4 are not copied to the destination interface. |
You can configure your mirror destination interface for each VNswitch to connect to a repeater. This section gives an example of how to mirror multiple VNswitch modules with one network analyzer on a DIGITAL DECrepeater. The configuration criteria for this example are:
The VNswitch module must be configured to conform to the requirements in the Mirror Restrictions section.
The VNswitch modules must reside in the same MultiSwitch 900.
A DIGITAL DECrepeater must be installed in the MultiSwitch 900.
DIGITAL clearVISN software must be available.
To configure multiple VNswitch modules using one network analyzer (Figure 13-1), perform the following steps:
Step | Action |
1 |
Configure your first VNswitch to the mirror interfaces and destination interface you want to use. |
2 |
Configure each additional VNswitch to the mirror interfaces and destination interface you want to use. |
3 |
Ensure that your DIGITAL DECrepeater has enough available ports to handle each destination interface and a port to connect a network analyzer. |
4 |
Using DIGITAL clearVISN software, connect the destination interface from the first VNswitch to an available repeater port. |
5 |
Repeat step 4 for each VNswitch you want to configure. |
6 |
Connect a network analyzer to an available repeater port. |
Your network analyzer is now capable of receiving packets from each VNswitch connected to the repeater.
To avoid losing packets to the network analyzer, ensure that the combined traffic from all destination interfaces connected by clearVISN to the DECrepeater does not exceed 10 Mb/s.
The following table provides a list of the mirror commands, with a description and example of each:
Command |
Description |
Clear |
Clears the destination interface, all the transmit interface, and all the receive interfaces. Example: Mirror Config> clear |
Enable/Disable |
Enables/disables the mirror destination interface to which mirror packets will be sent. Only one destination interface per VNswitch are allowed. Example 1: Mirror Config> enable 5 Example 2: Mirror Config> disable |
List |
Displays the destination interface, all the transmit interfaces and all the receive interfaces. Example: Mirror Config> list |
Set |
Sets a mirror interface on an Ethernet port. The interface can be set to mirror receive packets, transmit packets, both or none. When an interface is set to none, the mirror interface is disabled. Example 1: Mirror Config> set transmit 1-5 Example 2: Mirror Config> set receive 2,3,4 Example 3: Mirror Config> set both 1-12 Example 4: Mirror Config> set neither 6 |
The VNswitch Remote Network Monitoring (RMON) agent allows you to configure the VNswitch so that it independently monitors its own MIB variables and network traffic. The VNswitch RMON agent supports the Alarm and Event MIB groups and adheres to RMON MIB RFC 1757 for Ethernet objects.
The alarm group allows you to configure the VNswitch so that it monitors its own MIB variables. If the value of a monitored variable crosses its configured thresholds, the RMON agent generates an event. The event group associates an event with a set of actions. Two actions are defined: generate an SNMP trap message and add an entry to the event group log table.
You can configure alarms and events from a network management application, such as a MIB browser, that uses SNMP. You can also use the VNswitch CLI to read and write MIB variables in the alarm and event groups.
You can separately configure the Event Logging System (ELS) to generate an ELS event whenever an alarm generates an RMON event. Otherwise, the RMON event group and ELS are independent of each other.
Alarms and events are stored in NVRAM (nonvolatile RAM) memory and are preserved if you power cycle the VNswitch. You can delete individual table entries by using the RMON CLI delete command or you can use SNMP to set the table entry status to invalid. You can also use the clear RMON command from the Config prompt to delete all RMON table entries.
If you use SNMP to create, delete, or modify alarm and event table rows, you must follow the conventions for EntryStatus as specified in the RMON MIB (RFC 1757). You are not required to follow the EntryStatus conventions when you configure alarm and event table rows from the CLI.
The CLI correctly transitions row status.
The number of alarm and event table entries is limited to 256.
You cannot write more than one alarm table or event table row at a time in a single SNMP set PDU (Protocol Data Unit). If you do not specify all the values for a row in a set PDU, the default values specified in Table 13-1 and Table 13-2 are used. The CLI uses these default values only the first time you enter an alarm or event from the CLI. Then the CLI uses the values you last entered as a default.
Table 13-1 shows the variables and the default values for the set alarm command.
Table 13-1: RMON Set Alarm Command Parameters
Alarm Variable |
Default Value |
Alarm Index |
1 |
Alarm Status |
valid |
Alarm Interval |
1 |
Alarm Variable |
[0.0] |
Alarm Sample Type |
deltaValue |
Alarm Value |
0 |
Startup Alarm |
risingOrFallingAlarm |
Rising Alarm Threshold |
0 |
Falling Alarm Threshold |
0 |
Rising Event Index |
0 |
Falling Event Index |
0 |
Alarm Owner |
Null string |
Alarm Description |
Null string |
Table 13-2 shows the variables and the default values for the set event command.
Table 13-2: RMON Set Event Command Parameters
Event Variable |
Default Value |
Event Index |
1 |
Event Status |
valid |
Event Description |
Null string |
Event Type |
log-and-trap |
Event Community |
Null string |
Event Owner |
Null string |
You can configure RMON alarms and events from a network management application, such as a MIB browser, that uses SNMP. You can also use the VNswitch CLI to read and write MIB variables in the alarm and event groups.
To access the RMON configuration process using the CLI, perform the following steps:
Step | Action |
1 |
From the Main
prompt (Main>), enter the following command: |
2 |
At the Config>
prompt, enter the following command: |
3 |
Press Return. The
following prompt is displayed: |
Once you have entered the RMON configuration process, you can execute the commands in Table 13-3.
Table 13-3: RMON Configuration Commands
Command |
Command Parameters |
add |
alarm |
set |
alarm |
delete |
alarm |
list |
alarm |
To access the RMON monitor process through SNMP, perform the following steps:
Step | Action |
1 |
From the Main
prompt (Main>), enter the following command: |
2 |
At the Monitor>
prompt, enter the following command: |
3 |
Press Return. The
following prompt is displayed: |
Once you have entered the RMON monitor process, you can execute the commands in Table 13-4.
Table 13-4: RMON Monitor Commands
Command Type |
Command Parameters |
delete |
log table |
list |
alarm |
exit |
|
To clear all configuration information for RMON, perform the following steps:
Step | Action |
1 | From the Main prompt (Main>), enter the following command: Main> config The Config> prompt is displayed. |
2 | At the Config> prompt, enter the following command: Monitor>clear rmon |
3 | Press Return. The following message is displayed: You are about to clear all RMON configuration information *** WARNING *** This will invoke an automatic RESTART Are you sure you want to do this (Yes or [No]): |
4 | If you are certain you want to clear the information, enter Yes. |
To display RMON information, perform the following steps:
Step | Action |
1 | From the Main prompt (Main>), enter the following
command: Main> monitor The Monitor> prompt is displayed. |
2 | At the Monitor> prompt, enter the following command: Monitor> interface statistics n where n is the interface number for which you want statistics. |
3 | Press Return. RMON statistics information is displayed in the format shown in the example, along with other interface information. |
The following sections provide a configuration example. In this example, whenever the number of received SNMP packets increases, the VNswitch generates a risingAlarm trap to the community rmon-trap that has an IP address of 16.20.48.46.
The following procedure describes how to configure SNMP with a new community named rmon-trap with an IP address of 16.20.48.46:
Step | Action |
1 |
At the Config> prompt, enter snmp. |
2 |
Press Return. The SNMP community rmon-trap is now configured. |
The following sections describe how to configure RMON so that it generates a rising alarm trap if the MIB variable snmpInPkts.0 (oid 1.3.6.1.2.1.11.1.0) increases by more than zero over a 1-second interval. This is accomplished by creating an event entry and an alarm entry.
Creating an Event Entry
To create an event entry with an event type snmp-trap and an event community rmon-trap, perform the following steps:
Step | Action |
1 |
At the Config> prompt, enter rmon. |
2 |
At the RMON Config> prompt, enter add event. |
3 |
Enter the event description, type,
community, and owner. |
4 |
Press Return. The following is
displayed: |
Creating an Alarm Entry
To create an alarm entry for the above event entry, perform the following steps:
Step | Action |
1 |
At the RMON
Config> prompt, enter add alarm. |
2 |
Press Return. The
following is displayed: |
Summary
In the RMON example, whenever the VNswitch receives an SNMP request (snmpInPkts.0 increases by 1 or more), it sends an RMON risingAlarm trap.