tracert vc

Function

The tracert vc command checks the status of a PW or locates a faulty node on a PW in the Down state.

Format

tracert vc vc-type pw-id [ peer-address ] [ -exp exp-value | -f first-ttl | -m max-ttl | -r reply-mode | -t timeout-value | -g ] ^* label-alert [ no-control-word ] [ full-lsp-path ] [ pipe | uniform ] [ detail ] [ bypass -si { interface-name | interface-type interface-number } ]

tracert vc vc-type pw-id [ peer-address ] [ -exp exp-value | -f first-ttl | -m max-ttl | -r reply-mode | -t timeout-value | -g ] ^* control-word [ remote remote-ip-address ] [ full-lsp-path | ptn-mode ] [ pipe | uniform ] [ detail ] [ bypass -si { interface-name | interface-type interface-number } ]

tracert vc vc-type pw-id [ peer-address ] [ -exp exp-value | -f first-ttl | -m max-ttl | -r reply-mode | -t timeout-value | -g ] ^* normal [ no-control-word ] [ remote remote-ip-address ] [ full-lsp-path ] [ pipe | uniform ] [ detail ] [ bypass -si { interface-name | interface-type interface-number } ]

Parameters

Parameter	Description	Value
vc-type	Specifies the encapsulation type of a local PW.	Encapsulation types supported: Other encapsulation types: cep: This encapsulation type is used for CEP services. ethernet: This encapsulation type is used when Ethernet packets do not carry VLAN information. ip-interworking: This encapsulation type is used for interworking between Huawei devices. ip-layer2: This encapsulation type is used for interworking between Huawei devices and non-Huawei devices. vlan: This encapsulation type is used when Ethernet packets carry VLAN information.
pw-id	Specifies the ID of a local PW.	The value is an integer ranging from 1 to 4294967295.
peer-address	Specifies the peer LSR ID of the local PW.	The value is in dotted decimal notation.
-exp exp-value	Specifies the EXP value in the outer label of an MPLS echo request packet.	The value is an integer ranging from 0 to 7. The default value is 0.
-m max-ttl	Specifies the maximum TTL.	The value is an integer ranging from 1 to 255, and must be greater than the value of first-ttl. The default value is 30.
-r reply-mode	Specifies the mode in which the peer returns MPLS Echo Reply packets.	The value is an integer ranging from 1 to 4. The default value is 2. 1: no reply. 2: reply with an IPv4 or IPv6 UDP packet carrying the router-alert option. 3: reply with an IPv4 or IPv6 UDP packet carrying the router-alert option. 4: reply through the control channel of the application plane.
-t timeout-value	Specifies the period of the time to wait for an MPLS echo reply packet.	The value is an integer ranging from 0 to 65535, in milliseconds. The default value is 2000.
-g	Indicates MPLS packet fragmentation for an NQA test instance.	-
detail	Displays details carried in MPLS echo reply packets.	-
-f first-ttl	Specifies the first TTL value.	The value is an integer ranging from 1 to 255.
label-alert	Indicates that the router alert label is encapsulated into the MPLS echo request packet.	-
no-control-word	Indicates that the control word is not encapsulated into the MPLS echo request packet.	-
full-lsp-path	Displays the responses from all nodes along the LSP through which the MPLS echo request packets. If this parameter is not specified, only the responses from the PW nodes along the LSP are displayed.	-
pipe	Specifies the pipe mode. When a probe packet passes through the MPLS domain, the ingress reduces the IP TTL value in packets by one and sets the MPLS TTL to a specific value. Transit nodes only process the MPLS TTL. When the egress receives the packets, it removes the MPLS label carrying the MPLS TTL from each packet and reduces the IP TTL value by one.	-
uniform	Specifies the uniform mode. When IP TTL of the probe packet enter the MPLS network, the ingress reduces the IP TTL value by one and copies the IP TTL value to the MPLS TTL field. Each transit node only processes the MPLS TTL. The egress reduces the MPLS TTL by one, compares the MPLS TTL with the IP TTL, and obtains the smaller value to map it to the IP TTL.	-
bypass	Forwards packets through a specified public bypass LSP of a PW. If an inbound interface is specified in CLI mode to perform bypass LSP detection, the packets from the initiator are forwarded through a public bypass LSP. In a hybrid load balancing scenario, if multiple bypass LSPs exist, packets are forwarded through a randomly selected LSP rather than any specified bypass LSP. For the transmission of reply packets, the PEs at both ends of a PW must have protection paths configured. Otherwise, when the peer PE does not have any public bypass LSP, PW tracert reply packets cannot be returned.	-
-si interface-name	Specifies the name of a simulated inbound interface. The inbound interface of MPLS Echo Request packets is configured to simulate packet sending on the remote device and check whether the forwarding path of packets entering from the inbound interface is faulty.	-
interface-type	Specifies the type of a simulated inbound interface. The inbound interface of MPLS Echo Request packets is configured to simulate packet sending on the remote device and check whether the forwarding path of packets entering from the inbound interface is faulty.	-
interface-number	Specifies the number of a simulated inbound interface. The inbound interface of MPLS Echo Request packets is configured to simulate packet sending on the remote device and check whether the forwarding path of packets entering from the inbound interface is faulty.	-
control-word	Indicates that the control word is encapsulated into the MPLS echo request packet.	-
remote remote-ip-address	Specifies the remote IP address. By default, the system searches for the IP address of the next hop based on the PW ID on the local PE. If label-alert is configured, you can specify the IP address or the destination for any switch node.	The value is in dotted decimal notation.
ptn-mode	Specifies the PTN-Interworking mode.	-
normal	Indicates the normal mode where the router alert label and control word are not encapsulated into the MPLS echo request packet.	-

Views

All views

Default Level

0: Visit level

Task Name and Operations

Task Name	Operations
sla	execute

Usage Guidelines

Usage Scenario

If a fault occurs on the PW, the ping vc command can be used to check the connectivity of the network, and the tracert vc command can be used to locate the fault and provide information for fault diagnosis. If a PW is Up, the ping vc command can be used to locate a fault on the PW, such as an incorrect or dropped forwarding entry. If a PW is down, the tracert vc command must be used to locate the faulty node on the PW.

You can run the tracert vc command to check the PW in the following scenarios:

VLL networking
In the PWE3 VLL networking, a PW tracert is initiated to view information about SPEs and Ps along the path that the packet travels on, from source to destination. The PW tracert is used to check the connectivity of the PW and locate any faults on the network.
The PWE3 VLL PW tracert can be performed in control word, label alert, or TTL mode. The default mode is label alert.
To locate a fault on a VLL network by sending probe packets encapsulated with the control word, you can run the tracert vc pw-type pw-id control-word command.
To locate a fault on a VLL network by sending ordinary probe packets that are not encapsulated with the control word or router alert label, run the tracert vc pw-type pw-id command.
The TTL value of the PW Tracert Request packet is incremented by 1. Each time the switch node (P node) receives an echo request packet after the TTL value of the packet expires, it sends the echo request packet to the LSPV module.
VPLS networking
TheLDP VPLS PW tracert only supports the label alert mode. If an optional PW ID is configured and specified, the PW corresponding to the PW ID is monitored. If the PW ID is not specified, the PW corresponding to the VSI ID is monitored.

Prerequisites

Ensure that the UDP module of each node is working properly; otherwise, the tracert operation will fail.
Ensure that the MPLS module of each node is enabled and is working properly.
Ensure that the ICMP module of each node works properly; otherwise, "timeout" is displayed.

Implementation Procedure

The execution process of the tracert vc command is as follows:

1.The source sends an MPLS Echo Request packet with TTL 1. After the TTL times out, the first hop sends an MPLS Echo Reply packet to the source.

2.The source sends an MPLS Echo Request packet with TTL 2. After the TTL times out, the second hop sends an MPLS Echo Reply packet to the source.

3.The source sends an MPLS Echo Request packet with TTL 3. After the TTL times out, the third hop sends an MPLS Echo Reply packet to the source.

4.The preceding steps continue until the MPLS Echo Request packet reaches the destination.

When the device on the destination hop receives the MPLS Echo Request packet, it will respond with an MPLS Echo Reply packet, indicating that the tracert test ends. The purpose behind this is to record the source of each ICMP timeout packet to provide a trace of the path the packet took to reach the destination.

Configuration Impact

In control word mode, if a switch node receives an MPLS Echo Request packet whose TTL does not time out, it does not send the packet to the CPU. In this mode, the source obtains only a little PW information and cannot obtain information about the downstream of the transit node.

In router alert mode, a transit node sends the received MPLS Echo Request packets to the CPU. In this mode, the source obtains a lot of PW information. This mode, however, affects the device performance when the traffic volume is heavy.

Precautions

When the probe packet reaches the egress or the TTL reaches the upper threshold, the PW tracert is terminated.
You can press Ctrl+C to terminate the execution of the tracert vc command.
In the scenario where a PE is single-homed to an SPE and two multi-hop PWs are deployed for PW redundancy, end-to-end detection cannot be performed for the secondary PW if services are transmitted over the primary PW, or for the primary PW if services are transmitted over the secondary PW.
.

Example

# Run the tracert vc command to check the connectivity of the bypass LSP of the PW of simulated inbound interface GigabitEthernet 0/1/1.1.

<HUAWEI> tracert vc vlan 100 control-word bypass -si GigabitEthernet0/1/1.1
PW Trace Route : FEC 128 PSEUDOWIRE (NEW). Type = vlan, ID = 100, press CTRL_C to break
TTL    Replier            Time    Type      Downstream
0                                 Ingress   10.1.1.1/[321542 321543 33106 33249 65557 ]
4      1.1.1.9            3ms     Egress

**Table 1** Description of the **tracert vc** command output
Item	Description
PW Trace Route : FEC 128 PSEUDOWIRE (NEW). Type = x, ID = x, press CTRL_C to break	Return value of the PW trace test.
Type	Node type: Ingress. Transit. Egress.
TTL	TTL value in an echo request packet. It represents the number of hops of the tunnel an echo request packet passes.
Replier	IP address of the node sending MPLS echo reply packets.
Time	Time taken to process a packet.
Downstream	IP address and label of the downstream node.