Dell Command Line Reference Guide for the S4048–ON System



Trace a multicast route from the source to the receiver.

mtrace [vrf vrf-name] {source-address/hostname} [destination-address/hostname] [group-address/hostname]
vrf vrf-name
Enter the keyword vrf followed by the name of the VRF. If VRF name is not mentioned, the default VRF will be used. Mtrace is not supported for management VRF.
source-address/ hostname
Enter the source IP address in dotted decimal format (A.B.C.D). This is a unicast address of the beginning of the path to be traced.
destination-address/ hostname
Enter the destination (receiver) IP address in dotted decimal format (A.B.C.D). If omitted, the mtrace starts from the system at which the command is typed.
Enter the multicast group address in dotted decimal format (A.B.C.D). If group address is not given then software shall invokes a weak mtrace. A weak mtrace is one that follows the RPF path to the source, regardless of whether any router along the path has multicast routing table state
Command Modes
EXEC Privilege
Command History
Re-introduced the mtrace command on the Dell EMC Networking OS.
Expanded to support originator.
Expanded to support the intermediate (transit) router.
Usage Information

Mtrace is an IGMP based protocol that provides a multicast trace route facility and is implemented according to the IETF draft “A trace route facility for IP Multicast” (draft-fenner-traceroute-ipm-01.txt). Dell EMC Networking OS supports the Mtrace client and transit functionality.

As an Mtrace client, Dell EMC Networking OS transmits Mtrace queries, receives, parses, and prints out the details in the response packet received.

A transit or intermediate router, forwards mtrace requests to the RPF neighbor after appending its response block to the packet. In case it is the first hop router, it sends a response.

As an Mtrace transit or intermediate router, Dell EMC Networking OS returns the response to Mtrace queries. After receiving the Mtrace request, Dell EMC Networking OS computes the RPF neighbor for the source, fills in the request and the forwards the request to the RPF neighbor.

Type Ctrl-C to abort.

Querying reverse path for source to destination via group
From source (?) to destination (?)

|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
  0          -->    Destination
 -1          PIM   Reached RP/Core      
 -2  PIM       -         
 -3          PIM       -         
 -4    -->    Source
The mtrace command traverses the path of the response data block in the reverse direction of the multicast data traffic. The mtrace command traverses the reverse path to the source from the destination. As a result, the tabular output of the mtrace command displays the destination details in the first row, followed by the RPF router details along the path in the consequent rows, and finally the source details in the last row. The tabular output contains the following columns:
  • Hop — a hop number(counted negatively to indicate reverse-path)
  • OIF IP — outgoing interface address
  • Proto — multicast routing protocol
  • Forwarding code — error code as present in the response blocks
  • Source Network/Mask — source mask

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