Dell EMC Configuration Guide for the S4048T–ON System 9.14.2.4

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Printing Multicast Traceroute (mtrace) Paths

Dell EMC Networking OS supports Multicast traceroute.

MTRACE is an IGMP-based tool that prints the network path that a multicast packet takes from a source to a destination, for a particular group. Dell EMC Networking OS has mtrace client and mtrace transit functionality.

MTRACE Client — an mtrace client transmits mtrace queries and print the details from received responses.
MTRACE Transit — when a Dell EMC Networking system is an intermediate router between the source and destination in an MTRACE query, Dell EMC Networking OS computes the RPF neighbor for the source, fills in the request, and forwards the request to the RPF neighbor. When a Dell EMC Networking system is the last hop to the destination, Dell EMC Networking OS sends a response to the query.

To print the network path, use the following command.

Print the network path that a multicast packet takes from a multicast source to receiver, for a particular group.

EXEC Privilege mode

mtrace multicast-source-address multicast-receiver-address multicast-group-address

From source (?) to destination (?)

----------------------------------------------------------------------------------------
|Hop|     OIF IP              |Proto|   Forwarding Code            |Source Network/Mask|
----------------------------------------------------------------------------------------
  0    “destination ip(to)” -->    Destination
 -1    “Outgoing intf addr”   “Proto”   “Err/fwd code if present”   “Src Mask”
 -2    “Outgoing intf addr”   “Proto”   “Err/fwd code if present”   “Src Mask”
            .
            .
-“n”  “source ip(from)” -->  Source
-----------------------------------------------------------------------------------------

The mtrace command traverses the path of the response data block in the reverse direction of the multicast data traffic. 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

Example of the mtrace Command to View the Network Path

The following is an example of tracing a multicast route.

R1>mtrace 103.103.103.3 1.1.1.1 226.0.0.3
Type Ctrl-C to abort.

Querying reverse path for source 103.103.103.3 to destination 1.1.1.1 via group 226.0.0.3
From source (?) to destination (?)

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  1.1.1.1          -->    Destination
 -1  1.1.1.1          PIM   Reached RP/Core   103.103.103.0/24      
 -2  101.101.101.102  PIM       -             103.103.103.0/24      
 -3  2.2.2.1          PIM       -             103.103.103.0/24      
 -4  103.103.103.3    -->    Source
------------------------------------------------------------------

The following table explains the output of the mtrace command:

Table 1. mtrace Command Output — Explainedmtrace Command Output — Explained
Command Output	Description
Querying reverse path for source 103.103.103.3 to destination 1.1.1.1 via group 226.0.0.3	mtrace traverses the reverse path from the given destination to the given source for the given group
From source (?) to destination (?)	In case the provided source or destination IP can be resolved to a hostname the corresponding name will be displayed. In cases where the IP cannot be resolved, it is displayed as (?)
0 1.1.1.1 --> Destination	The first row in the table corresponds to the destination provided by the user.
-1 1.1.1.1 PIM Reached RP/Core 103.103.103.0/24	The information in each of the response blocks is displayed as follows: o (-1) Hop count is always a negative number to indicate reverse path o (1.1.1.1) Outgoing interface address at that node for the source and group o (PIM) Multicast protocol used at the node to retrieve the information o (Reached RP/Core) Forwarding code in mtrace to denote that RP node is reached o (103.103.103.0/24) Source network and mask. In case (*G) tree is used, this field will have the value as (shared tree). In case no value is noted in the record or in case of error like No Route or Wrong Last Hop the value (default) will be displayed
-4 103.103.103.3 --> Source	The last line in the table corresponds to the source address provided by the user.