Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 

What is the Probe Command?

 

RFC 8335, PROBE: A Utility for Probing Interfaces, describes the Probe utility. Probe is a network diagnostic tool similar to Ping that can be used to query the status of a probed interface on a node. The Probe command require bidirectional connectivity between the probing interface and the proxy interface. The proxy interface can reside on the same node as the probed interface, or it can reside on a node to which the probed interface is directly connected. Probe uses ICMP Extended Echo/Reply messages for communication between the probing interface and the proxy interface. This utility helps in scenarios where bidirectional connectivity between the probing and probed interfaces is lacking. For instance, if the probed interface is an unnumbered interface, or if the probed interface is assigned a different address family. In both cases you can use the Probe command to confirm if the probed interface is reachable from the proxy. The proxy interface learns details about the probed interface by inspecting its local ARP and NDP entries.

The first figure shows R0 as the probing node, R1 as the proxy node, and R2 as the probed node. In the second figure the R1 node functions in both the proxy and probed node roles:

Enabling the Probe command

To enable the probe command, configure the extended-echo configuration statement at the [edit system] hierarchy level on the proxy node.

Note

You do not need to enable the extended-echo configuration statement on the probing or probed nodes.

Using the Probe command

You can probe using the remote address of the probed device when the proxy and probed nodes are not the same. That is, when the proxy and the probed nodes are two different nodes. The proxy interface learns the details of the probed interface from its local ARP or NDP entries associated with the probed node.

You can also probe using the following three options when the proxy and probed nodes are same:

  • By using the IP address

  • By using the interface name

  • By using the interface index

Note

1. You can probe for information with any one of these mandatory options. That is, by-remote-address, by-address, by-name, or by-index.

2. You can probe using the IPv4 or IPv6 address to query for the status of the IPv4 address. Likewise, you can probe using the IPv4 or IPv6 address to query for the status of the IPv6 address.

The following examples shows how to use the probe command.

Purpose

Use case 1: Probing when the proxy interface and the probed interface reside on two different nodes (proxy node (R1) and the probed node (R2)). Consider R0 as the probing node, R1 as the proxy node, and R2 as the probed node and change the details of the interfaces and IP addresses to match your network configuration. In this case, you can probe using by-remote-address option only.

Probe for the status of a remote IP address using a proxy interface.

Action

Example 1: From operational mode, probe for the status of the IP address 10.0.12.2 of the probed node (R2) using the by-remote-address option with the proxy IP address 10.0.1.10 of the proxy node (R1).

In this case, the proxy node provides the status of the probed interface based on the information associated with its local ARP and NDP entries. Use the count argument to control the number of probe request that are sent.

Note
  • In this example, the target address (10.0.12.2) is defined on the probed node. As a result, you can see a positive result, which confirms that the IP address is reachable on the probed node.

  • When you probe using the by-remote-address option, you can only determine if the probed interface is reachable. That is, if the probed interface is in reachable state, then by default, the probe packet statistics such as active, IPv4, and IPv6 are set to zero (0).

user@R0>probe 10.0.1.10 by-remote-address 10.0.12.2 count 1

Meaning

The proxy IP address (10.0.1.10) displays the status of the probed IP address (10.0.12.2). The output is verified with the following probe packet statistics:

  • code=0 indicates that there is no error.

  • state=2 indicates that the probed IP address 10.0.12.2 is reachable.

  • active=0 is set to zero and ignored upon receipt when you probe using the by-remote-address option.

  • IPv4=0 and IPv6=0 by default when you probe using the by-remote-address.

  • time=milliseconds ms indicates the time taken to receive the reply after the request is transmitted.

  • ttl is the IPv4 time to live value, which default to the maximum value.

Example 2: From operational mode, probe for the status of the IP address 10.0.12.22 of the probed node (R2) using the by-remote-address option with the proxy IP address 10.0.1.10 of the proxy node (R1).

As in Example 1, the proxy node provides the status of the probed interface based on the information associated with its local ARP and NDP entries. Use the count argument to control the number of probe request that are sent.

Note
  • In this example the target address (10.0.12.22) is not defined on the probed node. As a result, you expect to see a negative result, which confirms the IP address is not active on the probed node.

  • When you probe using the by-remote-address option, you can only determine if the probed interface is reachable. That is, if the probed interface is in reachable state, then by default, the probe packet statistics such as active, IPv4, and IPv6 are set to zero (0).

user@R0>probe 10.0.1.10 by-remote-address 10.0.12.22 count 1

Meaning

The proxy IP address (10.0.1.10) displays the status of the probed IP address (10.0.12.22). The output is verified with the following probe packet statistics:

  • code=3 indicates that there is no such entry in the ARP table. This is expected in this example because the probed IP address is not defined on either the proxy or probed nodes.

  • state=0 is a required setting when the code bit is set to a non-zero state and the probed interface does not reside on the proxy node. Here, the probed IP address resides on the probed node, and the code bit is set to a 3.

  • active=0 is set to zero and ignored upon receipt when you probe using the by-remote-address option.

  • IPv4=0 and IPv6=0 by default when you probe using the by-remote-address.

  • time=milliseconds ms indicates the time taken to receive the reply after the request is transmitted.

  • ttl is the IPv4 time to live value, which default to the maximum value.

Purpose

Use Case 2: Probing when proxy node and the probed node are the same. Consider R0 as the probing node, R1 as the proxy and the probed node. Change the details of the interfaces and IP addresses to match your network configuration.

Query for the status of the probed IP address through the proxy IP address

Action

From operational mode, probe for the status of the probed IP address 10.0.12.1 using the by-address option with the proxy IP address 10.0.1.10 at the proxy node (R1). The count argument is used to set the number of probe requests to 1.

user@R0>probe 10.0.1.10 by-address 10.0.12.1 count 1

Meaning

The proxy IP address, 10.0.1.10 displays the status of the probed IP address, 10.0.12.1. The output is verified with the following probe packet statistics:

  • code=0 indicates that the Probe request completed without error.

  • state=0 indicates that the probed interface is active and resides on the proxy node.

  • active=1 indicates that the probed interface is active.

  • IPv4=1 and IPv6=1 indicates that both IPv4 and IPv6 addresses are configured and available on the probed node.

  • time=milliseconds ms indicates the time taken to receive the reply after the request is transmitted.

  • ttl is the IP time to live value, which is set to the maximum hop count..

Purpose

Use Case 3: Query for the status of the IPv4 or IPv6 address using the interface index of the probed interface. (Probing when the proxy node and the probed node are the same. Consider R0 as the probing node, R1 as the proxy and the probed node. Change the details of the interfaces and IP addresses to match your network configuration.)

Action

From operational mode, probe for the status of the IPv4 or IPv6 address using the by-index option to specify the interface index of the probed interface. The count 2 argument causes 2 probe request to be generated. In this example the R1 node functions as both the proxy and probed nodes.

user@R0>probe 10.0.1.10 by-index 333 count 2

Meaning

The proxy IP address, 10.0.1.10 displays the status of the probed interface using the Logical interface index-id, 333. The output is verified with the following probe packet statistics:

  • code=0 indicates that the request is completed without error.

  • state=0 indicates that the probed interface is active and resides on the proxy node.

  • active=1 indicates that the probed interface is active.

  • IPv4=1 and IPv6=1 indicates that IPv4 and IPv6 addresses are configured on the probed node.

  • time=milliseconds ms indicates the time taken to receive the reply after the request is transmitted.

  • ttl is the IP time to live value..

Purpose

Use Case 4: Query the proxy interface for information about the probed interface that reside on the proxy node. (Probing when the proxy node and the probed node are the same. Consider R0 as the probing node, R1 as the proxy and the probed node. Change the details of the interfaces and IP addresses to match your network configuration.)

Action

From operational mode, probe for the status of the probed IP address using the by-address option while specifying the proxy node by its IPv6 address. The count argument is used to set the probe count to 1.

user@R0>probe 2001:db8:1::11 by-address 10.0.12.1 count 1

Meaning

The proxy IP address, 2001:db8:1::11 displays the status of the probed IP address, 10.0.12.1 that resides on the proxy device. The output is verified with the following probe packet statistics:

  • code=0 indicates that the probe request completes with out error.

  • state=0 indicates that the probed interface is active and resides on the proxy node.

  • active=1 indicates that the probed interface is active.

  • IPv4=1 and IPv6=1 indicates that both IPv4 and IPv6 addresses are configured on the probed interface.

  • time=milliseconds ms indicates the time taken to receive the reply after the request is transmitted.

  • hlim is the IPv6 hop-limit which defaults to the maximum value.

Purpose

Use case 5: Query for the status of the probed interface using the interface name. (Probing when the proxy node and the probed node are the same. Consider R0 as the probing node, R1 as the proxy and the probed node. Change the details of the interfaces and IP addresses to match your network configuration.)

Action

From operational mode, probe for the status of the probed interface using the interface name ge-0/0/1.0 using the IPv6 address of the proxy node 2001:db8:1::11.

user@R0> probe 2001:db8:1::11 by-name ge-0/0/1.0 count 1

Meaning

The proxy node with IPv6 address, 2001:db8:1::11 returns the status of the specified interface ge-0/0/1.0. The output is verified with the following probe packet statistics:

  • code=0 indicates that the probe request completes without error.

  • state=0 indicates that the probed interface is active on the proxy node.

  • active=1 indicates that the probed interface is active.

  • IPv4=1 and IPv6=1 indicates that the IPv4 and IPv6 addresses are available on the probed interface.

  • time=milliseconds ms indicates the time taken to receive the reply after the request is transmitted.

  • hlim is the maximum IPv6 hop-limit-value.

Related Documentation