Contents

Configuring MOD·· 1

Overview· 1

Restrictions and guidelines: MOD configuration· 1

Configuring common MOD·· 1

Configuring group MOD·· 2

Verifying and maintaining MOD·· 2

MOD configuration examples· 3

Example: Configuring common MOD to send packets through UDP· 3

 

Configuring MOD

Overview

Mirror On Drop (MOD) can detect packet drops during the forwarding process on the device. When a packet is dropped, MOD can send the packet drop reason and the characteristics of the dropped packet to the collector.

MOD uses the flow entries generated based on a flow group to detect dropped packets. For more information about flow groups, see flow group configuration in Telemetry Configuration Guide.

MOD works as follows:

1.     The device generates flow entries based on a flow group.

2.     Based on the MOD configuration, the device monitors packet drops for packets matching the flow entries.

3.     If a packet is dropped, the device sends the packet drop reason and the characteristics of the dropped packet (flow entry matching the packet) to the collector.

MOD includes common MOD and group MOD.

·     Common MOD—Monitors the drop reason list. The monitored drop reasons are mainly related to forwarding.

·     Group MOD—Monitors the drop reason groups. The monitored drop reasons are mainly related to output queues of ports.

When MOD monitors drop reason groups, MOD cannot identify the specific reason. To obtain the specific reason, you can map the concerned drop reason to the user-defined group, and then configure MOD to monitor the user-defined group.

Restrictions and guidelines: MOD configuration

MOD takes effect only on packets matching a flow group.

If an IP packet flow and a VXLAN packet flow arrive at the switch at an interval less than 0.0083 second, MOD can collect packet drop information for only the packet flow that arrives late.

Configuring common MOD

1.     Enter system view.

system-view

2.     Enter MOD view.

telemetry mod

3.     Configure the device ID for MOD.

device-id address

By default, no device ID is configured for MOD.

4.     Configure the encapsulation information for packets sent to the collector by MOD.

collector source-ip source-address destination-ip destination-address source-port source-port destination-port destination-port [ vlan vlan-id ]

By default, the encapsulation information for packets sent to the collector by MOD is not configured.

5.     Configure the packet drop reason list monitored by MOD.

reason-list { reason-list | all }

By default, no packet drop reasons is configured, and the device does not monitor packet drops.

For more information about the packet drop reason list, see the reason-list command in Telemetry Command Reference.

Configuring group MOD

1.     Enter system view.

system-view

2.     Enter MOD view.

telemetry mod

3.     Configure the device ID for MOD.

device-id address

By default, no device ID is configured for MOD.

4.     Configure the encapsulation information for packets sent to the collector by MOD.

collector source-ip source-address destination-ip destination-address source-port source-port destination-port destination-port [ vlan vlan-id ]

By default, the encapsulation information for packets sent to the collector by MOD is not configured.

5.     Return to system view.

quit

6.     (Optional.) Enter drop reason mapping view.

telemetry mod reason-group-map

7.     (Optional.) Configure the mappings between drop reasons and drop reason groups.

mapping reason-list { reason-list | all } group name

For the default setting, see the group-list command of MOD commands in Telemetry Command Reference.

8.     (Optional.) Return to system view.

quit

9.     Enter MOD view.

telemetry mod

10.     Configure the packet drop reason groups monitored by MOD.

group-list { group-list | all }

By default, no packet drop reason groups monitored by MOD are configured, and group MOD is disabled.

For more information about the packet drop reason list, see the group-list command in Telemetry Command Reference.

Verifying and maintaining MOD

To verify the MOD configuration, execute the following command in any view:

·     Display MOD configuration.

display telemetry mod [ slot slot-number ]

·     Display the mappings between drop reasons and drop reason groups.

display telemetry mod reason-list-map [ group [ group-name ] ] [ slot slot-number ]

MOD configuration examples

Example: Configuring common MOD to send packets through UDP

Network configuration

As shown in Figure 1, Host A and Host B access the external network through Device A and Device B. Some packets from the external network are missing on Host A. Configure MOD on the access device and aggregation device to identify whether packets are dropped during the forwarding process on the two devices.

Figure 1 Network diagram

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Prerequisites

Configure IP addresses for devices, and make sure they can reach each other at Layer 3.

Procedures

IMPORTANT: By default, interfaces on the device are disabled (in ADM or Administratively Down state). To have an interface operate, you must use the undo shutdown command to enable that interface.

 

1.     Configure Device A:

a.     Configure a flow group:

# Set the flow entry aging time to 10 minutes.

[DeviceA] telemetry flow-group aging-time 10

# Apply flow group 1.

[DeviceA] telemetry apply system-defined ip

b.     Configure MOD:

# Configure the device ID for MOD as 192.168.10.1.

[DeviceA] telemetry mod

[DeviceA-telemetry-mod] device-id 192.168.10.1

[DeviceA-telemetry-mod] quit

# Encapsulate the packets sent to the collector by MOD with the following information: source IP address 192.168.10.1, destination IP address 192.168.3.1, source port number 1000, and destination port number 2333.

[DeviceA-telemetry-mod] collector source-ip 192.168.10.1 destination-ip 192.168.3.1 source-port 1000 destination-port 2333

# Configure MOD to monitor all packet drop reasons.

[DeviceA-telemetry-mod] reason-list all

[DeviceA-telemetry-mod] quit

2.     Configure Device B.

Configure Device B in the same way Device A is configured except the device ID for MOD and the source IP address encapsulated in the packets sent to the collector.

Verifying the configuration

1.     Verify the configuration on Device A:

# Display the flow group configuration.

<DeviceA> display telemetry flow-group system-defined ip

Flow group named system-defined-ip (Successful)

  Template  :

    destination-ip

    destination-port

    protocol

    source-ip

    source-port

Aging time: 10 minutes

# Display the MOD configuration.

<DeviceA> display telemetry mod

Status             : Successful

Drop reason list:

  denied-vlan

  ipv4-dip-miss

  smac-equal-dmac

Sampler     : samp

Device ID   : 192.168.10.1

Transport protocol : udp

Collector

  Source IP        : 192.168.10.1

  Destination IP   : 192.168.3.1

  Source port      : 1000

  Destination port : 2333

2.     Verify the configuration on Device B.

The configuration on Device B is the same as the configuration on Device A except the device ID for MOD and the source IP address encapsulated in the packets sent to the collector. (Details not shown.)

3.     Verify the configuration on the collector.

When a packet destined for IP address 10.0.0.10 is dropped during the forwarding process on Device A and Device B, the collector can receive the packet drop reason and the characteristics of the dropped packet from the devices.