tracert lsp

Function

The tracert lsp command enables the system to trace the gateways along the BGP LSP from the source to the destination.

Format

Parameters

Parameter	Description	Value
-a source-ip	Specifies a source IP address of the MPLS Echo Request packet to be sent. If no source IP address is specified, the LSR-ID functions as the source address.	The value is in dotted decimal notation.
-exp exp-value	Specifies an EXP value of the MPLS Echo Request packet to be sent.	The value is an integer ranging from 0 to 7. The default value is 0.
-h ttl-value	Specifies a TTL value of the MPLS Echo Request packet to be sent. Carried in the IP header, the TTL field indicates the lifetime of the IP packet and specifies the maximum number of routers that the packet can pass through. The TTL value is set on the source and reduced by 1 each time the packet passes through one router. When the TTL value is reduced to 0, the packet is discarded. At the same time, a timeout packet is sent to notify the source.	The value is an integer ranging from 1 to 255. The default value is 30.
-r reply-mode	Specifies a mode in which the peer sends MPLS Echo Reply packets in response.	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. 3: reply with an IPv4 or IPv6 UDP packet that carries the Router Alert option. 4: reply through the control channel of the application plane.
-t time-out	Specifies a period of time for waiting for an MPLS Echo Reply packet.	The value is an integer ranging from 0 to 65535, in milliseconds. The default value is 2000.
-s size	Specifies a packet size.	The value is an integer ranging from 100 to 9600.
-g	Indicates MPLS packet fragmentation for an NQA test instance.	-
bgp destination-iphost	Specifies the destination IPv4 address or host name of a BGP LSP.	If the value is an IP address, it is in dotted decimal notation. If the value is a host name, it is a string of 1 to 255 case-sensitive characters, spaces not supported.
mask-length	Specifies the mask length of the destination address.	The value is an integer ranging from 0 to 32.
ip-address	Specifies the destination address in the IP header of an MPLS ping packet with the prefix of 127.0.0.0/8.	The value is in dotted decimal notation. The default value is 127.0.0.1.
detail	Displays details carried in MPLS Echo Reply packets.	-
nexthop next-address	Specifies a next hop address. In LSP load balancing scenarios, you can use this parameter to specify the next hop address to implement traffic forwarding.	The value is in dotted decimal notation.

Views

All views

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
tailmode1	execute

Usage Guidelines

Usage Scenario

The ping lsp command can be used to check the connectivity of LSPs on an MPLS network, and the tracert lsp command can be used to locate the faulty node.

The tracert lsp command uses MPLS Echo Request packets and MPLS Echo Reply packets to detect the connectivity of LSPs. Both Echo Request and Echo Reply packets are transmitted in the format of UDP packets through port 3503. The receiver distinguishes these two types of packets based on the port number. An MPLS Echo Request packet carries FEC information to be detected, and is sent along the same LSP as other packets carrying the same FEC information. In this manner, the connectivity of the LSP is checked. Echo Request packets are transmitted to the destination using MPLS, whereas MPLS Echo Reply packets are transmitted to the source using IP.

BGP LSP: You can run the tracert lsp bgp destination-iphost mask-length [ ip-address ] [ detail ] [ nexthop nexthop-address ] command on the ingress to initiate a tracert test to the egress to check the connectivity of a BGP LSP carrying IPv4 packets and locate the faulty node.

Prerequisites

Before initiating a trace test, ensure that the UDP module of each node works properly.
Ensure that the MPLS module of each node is enabled and works properly.
Ensure that the ICMP module of each node works properly. Otherwise, a message is returned, indicating the trace test times out.

Implementation Procedure

The process of the tracert lsp command is as follows:

The source sends an MPLS Echo Request packet with the TTL being 1. After the TTL times out, the first hop sends an MPLS Echo Reply packet to the source.
The source sends an MPLS Echo Request packet with the TTL being 2. After the TTL times out, the second hop sends an MPLS Echo Reply packet to the source.
The source sends an MPLS Echo Request packet with the TTL being 3. After the TTL times out, the third hop sends an MPLS Echo Reply packet to the source.
The preceding process proceeds until an MPLS Echo Request packet reaches the destination.
In each probe, when receiving an MPLS Echo Request packet, the device on the last hop replies with an MPLS Echo Reply packet, indicating that the trace test ends. In this manner, the result of each probe is displayed on the source, based on which you can find the path from the source to the destination.

Configuration Impact

To prevent the egress from forwarding a received MPLS Echo Request packet to another node, you can set the destination address in the IP header of the packet to a loopback address with the prefix being 127.0.0.0/8.

Example

# Initiate an LSP tracert test on an SR-MPLS TE policy tunnel.

<HUAWEI> tracert lsp sr-te policy policy-name test
LSP Trace Route FEC: Nil FEC, press CTRL_C to break.  
sr-te policy segment list:
Preference : 300; Path Type: main; Protocol-Origin : local; Originator: 0, 0.0.0.0; Discriminator: 300; Segment-List ID : 1;  Xcindex : 1
TTL   Replier            Time     Type       Downstream  
0                                Ingress    10.1.2.1/[13312 12]  
1     10.1.2.2           63 ms   Transit    10.1.2.2/[12 ]  
2     6.6.6.6            93 ms   Egress

sr-te policy segment list:
Preference : 400; Path Type: backup; Protocol-Origin : local; Originator: 0, 0.0.0.0; Discriminator: 400; Segment-List ID : 1;  Xcindex : 1
TTL   Replier            Time      Type       Downstream  
0                                Ingress    10.1.2.1/[13312 12]  
1     10.1.2.2           63 ms   Transit    10.1.2.2/[12 ]  
2     6.6.6.6            93 ms   Egress

# Initiate a general LSP tracert test.

<HUAWEI> tracert lsp general labels 20 40 -i Ethernet 0/1/1 nexthop 10.1.1.2
  LSP Trace Route FEC: Nil FEC , press CTRL_C to break.  
  TTL   Replier     Time    Type      Downstream  
  0                         Ingress   10.1.1.1/[20 40 ]  
  1     10.1.1.2    4 ms    Transit   10.1.1.2/[40 ]
  2     3.3.3.3     3 ms    Egress

# Initiate a tracert test on an SRv6 TE Policy manually configured.

<HUAWEI> tracert lsp segment-routing te ipv6 Tunnel 1 nli-fec
  LSP Trace Route FEC: SEGMENT ROUTING TE IPV6 SESSION QUERY Tunnel1 , press CTRL_C to break.
  TTL   Replier            Time    Type      Downstream
  0                                Ingress   2001:DB8::4:101:0:2
  1     2001:DB8:1::1            94 ms   Transit   2001:DB8::4:101:0:1
  2     2001:DB8:2::2            94 ms   Egress

# Initiate a tracert test on an SR-MPLS TE IPv4 tunnel dynamically created.

<HUAWEI> tracert lsp segment-routing auto-tunnel Tunnel10 version draft4
  LSP  Trace  Route  FEC: AUTO TE TUNNEL IPV4 SESSION QUERY Tunnel10 , press CTRL_C to break.
  TTL     Replier                   Time    Type      Downstream
  0                                         Ingress   10.1.1.2/[284688 ]
  1       10.1.1.2                  7 ms    Egress

# Trace the LSP to 1.1.1.1/32.

<HUAWEI> tracert lsp ip 1.1.1.1 32
  LSP Trace Route FEC: IPV4 PREFIX 1.1.1.1/32 , press CTRL_C to break.
  TTL    Replier            Time    Type      Downstream
  0                                 Ingress   10.1.1.1/[3 ]
  1      1.1.1.1            5       Egress

# Initiate a tracert test on an SR-MPLS TE IPv4 tunnel manually configured.

<HUAWEI> tracert lsp segment-routing te Tunnel10
  LSP  Trace  Route  FEC: AUTO TE TUNNEL IPV4 SESSION QUERY Tunnel10 , press CTRL_C to break.
  TTL     Replier              Time    Type      Downstream
  0                                    Ingress   10.1.1.2/[284688 ]
  1       10.1.1.2             7 ms    Egress

# Trace a TE tunnel.

<HUAWEI> tracert lsp te Tunnel 1
  LSP Trace Route FEC: TE TUNNEL IPV4 SESSION QUERY Tunnel1 , press CTRL_C to break.
  TTL    Replier            Time    Type      Downstream
  0                                 Ingress   10.1.1.1/[3 ]
  1      1.1.1.1            4       Egress

**Table 1** Description of the **tracert lsp** command output
Item	Description
Preference	Path preference.
Path Type	Path type: primary path/backup path.
Protocol-Origin	Protocol source: pecp. bgp. local. unknown.
Segment-List ID	Segment list ID.
Xcindex	Index of Xc.
TTL	TTL in an MPLS echo request packet. It indicates the number of hops of the tunnel, through which an echo request packet passes.
Replier	IP address of the node sending an MPLS echo reply packet.
Time	Round-Trip Time (RTT) value, in milliseconds.
Type	Type of a node. The value can be: Ingress. Transit. Egress.
Downstream	Address and label of a downstream device.
Originator	IP address of the end.
Discriminator	Identifier.