traceroute mpls lsp

traceroute mpls lsp [lsp_name | any host | prefix ipNetmask] {reply-mode [ip | ip-router-alert]} {{from from} {ttl ttl} {next-hop hopaddress}}


Traces the path an LSP takes for the specified FEC.

Syntax Description

lsp_name Specifies the LSP on which to send the MPLS echo request.
any Allows the echo request to be sent over any available LSP.
host Specifies the FEC using an ipaddress or hostname.
prefix Specifies a prefix.
ipNetmask Specifies the prefix address.
reply-mode Specifies the reply mode for the MPLS echo response.
ip Requests an IP UDP reply packet. This is the default mode.
ip-router-alert Requests an IP UDP reply packet with the IP Router Alert option.
from Specifies the IP address to be used as the source address in the MPLS echo request.
ttl Specifies the starting TTL hop value. The range is from 1 - 30. The default is 1.
hopaddress Specifies the next-hop address.


The maximum time-to-live value is 30 seconds.

Usage Guidelines

This command traces the path an LSP takes for the specified FEC. The traceroute command, with the mpls keyword option, works by repeatedly sending an MPLS echo request (or “MPLS Ping”). The TTL value is incremented for each successive MPLS echo request sent. The sending LSR waits 5 seconds before sending the next MPLS echo request. This operation continues until either the egress LSR for the FEC is reached, the maximum TTL value is reached, or the operation is interrupted. For each response received, the following information is displayed on the console:
  • IP address of the replying LSR
  • Return code
  • Indication of an MPLS echo reply timeout if no response was received

The FEC can be specified using the ipaddress or hostname via the host parameter. If the optional next-hop is specified, the MPLS echo request is sent along the LSP that traverses the specified node. This option is useful for tracing a specific LSP when multiple LSPs exist to the specified FEC. The lsp keyword may be used to specify a named LSP to trace. The selected LSP is specified by the lsp_name parameter. The any keyword indicates that the switch can trace any available LSP to the specified host.

The optional reply-mode keyword is used to specify the reply mode for the MPLS echo response. When the ip option is specified, the MPLS echo reply is routed back to the sender in a normal IPv4 packet. When the ip-router-alert option is specified, the MPLS echo reply is routed back to the sender in an IPv4 packet with the Router Alert IP option set. Additionally, if the ip-router-alert option is specified and the reply route is via an LSP, the Router Alert Label is pushed onto the top of the label stack. If the reply-mode is not specified, the reply-mode ip option applies.

The optional ttl keyword specifies the starting TTL value in the MPLS echo request packet. Within each router along the path, the TTL value is decremented. When the TTL value reaches zero, the LSR drops the packet and replies with a TTL-expired ICMP message. The originating LSR responds by displaying the hop for which the TTL expired. To discover all hops to a destination, the originating router repeats the MPLS echo request and increments the TTL start value by one each time until the destination is reached. The maximum TTL is 30, so the traceroute command terminates if the destination is not reached in 30 hops.

If the ttl keyword is omitted, the starting TTL value is 1. If you specify a larger starting TTL value, initial hops are excluded from the traceroute display. For example, if you specify a start TTL value of 5, the TTL value does not decrement to 0 at the first four routers, so the fifth hop router is the first to appear in the traceroute command display.

The from keyword is used to specify the source IP address used in the MPLS echo request. This is the IP address used by the target LSR to send the MPLS echo reply. If not specified, the OSPF router ID is used.


The following example shows a sample display for the traceroute command:

# traceroute mpls lsp prefix
traceroute to, 30 hops max
1                                 5 ms        5 ms        2 ms
2                                2 ms        1 ms        2 ms
# traceroute mpls lsp lsp598
traceroute to lsp598, 30 hops max
1                                 6 ms        1 ms        5 ms
2                                 3 ms        2 ms        2 ms
3                                 3 ms        4 ms        3 ms


This command was first available in ExtremeXOS 11.6.

Platform Availability

This command is available only on the platforms that support MPLS as described in the ExtremeXOS and Switch Engine 31.7 Feature License Requirements document.