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Dell EMC Networking OS Configuration Guide for the S5048F–ON System 9.14.2.4

PDF

mtrace Scenarios

This section describes various scenarios that may result when an mtrace command is issued.

The following table describes various scenarios when the mtrace command is issued:

Table 1. Mtrace ScenariosVarious mtrace scenarios
Scenario Output
When you want to trace a route with the multicast tree for a source, group, and destination, you can specify all the parameters in the command. Mtrace will trace the complete path from source to destination by using the multicast tables for that group. 
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
------------------------------------------------------------------
You can issue the mtrace command specifying the source multicast tree and multicast group without specifying the destination. Mtrace traces the complete path traversing through the multicast group to reach the source. The output displays the destination and the first hop (-1) as 0 to indicate any PIM enabled interface on the node. 
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 via group 226.0.0.3
From source (?) to this node

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  0.0.0.0*         -->    Destination
 -1  0.0.0.0*         PIM       -             103.103.103.0/24      
 -2  2.2.2.1          PIM       -             103.103.103.0/24      
 -3  103.103.103.3    -->    Source
------------------------------------------------------------------
* - Any PIM enabled interface on this node
You invoke a weak mtrace request by specifying only the source without specifying the mulicast tree or multicast group information for the source. Mtrace traces a path towards the source by using the RPF neighbor at each node. 
R1>mtrace 103.103.103.3
Type Ctrl-C to abort.

Querying reverse path for source 103.103.103.3 via RPF
From source (?) to this node

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  0.0.0.0*         -->    Destination
 -1  0.0.0.0*         PIM       -             103.103.103.0/24      
 -2  2.2.2.1          PIM       -             103.103.103.0/24      
 -3  103.103.103.3    -->    Source
------------------------------------------------------------------
* - Any PIM enabled interface on this node

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

Querying reverse path for source 103.103.103.3 to destination 1.1.1.1 via RPF
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       -             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
------------------------------------------------------------------
You can issue the mtrace command by providing the source and multicast information. However, if the multicast group is a shared group (*,G), then mtrace traces the path of the shared tree until it reaches the RP. The source mask field reflects the shared tree that is being used to trace the path. The shared tree is used even in case where the source provided is not valid. 
R1>mtrace 3.3.3.3 1.1.1.1 226.0.0.3
Type Ctrl-C to abort.

Querying reverse path for source 3.3.3.3 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         -           shared tree          
 -2  12.12.12.1       PIM   Reached RP/Core   shared tree          
------------------------------------------------------------------
When you issue the mtrace command with the source and multicast group information, if a multicast route is not present on a particular node, then the NO ROUTE error code is displayed on the node. In this scenario, the Source Network/Mask column for that particular node displays the the value as default. 
R1>mtrace 6.6.6.6 4.4.4.5 234.1.1.1
Type Ctrl-C to abort.

Querying reverse path for source 6.6.6.6 to destination 4.4.4.5 via group 234.1.1.1
From source (?) to destination (?)

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  4.4.4.5          -->    Destination
 -1  4.4.4.4          PIM        -            6.6.6.0/24        
 -2  20.20.20.2       PIM        -            6.6.6.0/24
 -3  10.10.10.1       PIM    No route         default     
------------------------------------------------------------------
If you invoke a weak mtrace query (without the multicast group details) and the RPF neighbor on one of the nodes to the source is not PIM enabled, the output of the command displays a NO ROUTE error code in the Forwarding Code column. In the command output, the entry for that node in the Source Network/Mask column displays the value as default. 
R1>mtrace 6.6.6.6 4.4.4.5 
Type Ctrl-C to abort.

Querying reverse path for source 6.6.6.6 to destination 4.4.4.5 via group 234.1.1.1
From source (?) to destination (?)

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  4.4.4.5          -->    Destination
 -1  4.4.4.4          PIM        -            6.6.6.0/24        
 -2  20.20.20.2       PIM        -            6.6.6.0/24
 -3  10.10.10.1       PIM    No route         default     
------------------------------------------------------------------
If a multicast tree is not formed due to a configuration issue (for example, PIM is not enabled on one of the interfaces on the path), you can invoke a weak mtrace to identify the location in the network where the error has originated. 
R1>mtrace 6.6.6.6 4.4.4.5 
Type Ctrl-C to abort.

Querying reverse path for source 6.6.6.6 to destination 4.4.4.5 via RPF
From source (?) to destination (?)

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  4.4.4.5          -->    Destination
 -1  4.4.4.4          PIM                     6.6.6.0/24        
 -2  20.20.20.2       PIM                     6.6.6.0/24
 -3  10.10.10.1       PIM  Multicast disabled 6.6.6.0/24   
------------------------------------------------------------------
If the destination provided in the command is not a valid receiver for the multicast group, the last hop router for the destination provides the WRONG LAST HOP error code. If the last-hop router contains a path to the source, the path is traced irrespective of the incorrect destination. 
R1>mtrace 6.6.6.6 5.5.5.5 234.1.1.1
Type Ctrl-C to abort.

Querying reverse path for source 6.6.6.6 to destination 4.4.4.5 via group 234.1.1.1
From source (?) to destination (?)

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  5.5.5.5          -->    Destination
 -1  5.5.5.4          PIM    Wrong Last-Hop   6.6.6.0/24        
 -2  20.20.20.2       PIM                     6.6.6.0/24
 -3  10.10.10.1       PIM                     6.6.6.0/24
 -4  6.6.6.6          -->      Source
------------------------------------------------------------------
If a router in the network does not process mtrace and drops the packet resulting in no response, the system performs an expanding-hop search to trace the path to the router that has dropped mtrace. The output of the command displays a ‘*’ indicating that no response is received for an mtrace request. The following message appears when the system performs a hop-by-hop search: “switching to hop-by-hop:” 
R1>mtrace 99.99.99.99 1.1.1.1
Type Ctrl-C to abort.

Querying reverse path for source 99.99.99.99 to destination 1.1.1.1 via RPF
From source (?) to destination (?)
 * * * * switching to hop-by-hop:
-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  1.1.1.1          -->    Destination
 -1  1.1.1.1          PIM       -             99.99.0.0/16          
 -2  101.101.101.102  PIM       -             99.99.0.0/16                                                                                                                 
 -3  2.2.2.1          PIM       -             99.99.0.0/16          
 -4  * * * * 
------------------------------------------------------------------
If there is no response for mtrace even after switching to expanded hop search, the command displays an error message. 
R1>mtrace 99.99.99.99 1.1.1.1
Type Ctrl-C to abort.

Querying reverse path for source 99.99.99.99 to destination 1.1.1.1 via RPF
From source (?) to destination (?)
 * * * * switching to hop-by-hop:
-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0 1.1.1.1          -->    Destination
 -1  * * * * 
------------------------------------------------------------------
Timed out receiving responses
Perhaps no local router has a route for source, the receiver is not
a member of the multicast group or the multicast ttl is too low.
While traversing the path from source to destination, if the mtrace packet exhausts the maximum buffer size of the packet, then NO SPACE error is displayed in the output. You can initiate a new mtrace query by specifying the destination as the last IP address from the output of the previous trace query. 
R1>mtrace 99.99.99.99 1.1.1.1
Type Ctrl-C to abort.

Querying reverse path for source 99.99.99.99 to destination 1.1.1.1 via RPF
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       -             99.99.0.0/16          
 -2  101.101.101.102  PIM       -             99.99.0.0/16                                                                                                                 
 -3  2.2.2.1          PIM       -             99.99.0.0/16          
 .
 .
 .
-146  17.17.17.17      PIM  No space in packet 99.99.0.0/16
------------------------------------------------------------------
In a valid scenario, mtrace request packets are expected to be received on the OIF of the node. However, due to incorrect formation of the multicast tree, the packet may be received on a wrong interface. In such a scenario, a corresponding error message is displayed. 
R1>mtrace 6.6.6.6 4.4.4.5 
Type Ctrl-C to abort.

Querying reverse path for source 6.6.6.6 to destination 4.4.4.5 via RPF
From source (?) to destination (?)

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  4.4.4.5          -->    Destination
 -1  4.4.4.4          PIM                     6.6.6.0/24        
 -2  20.20.20.2       PIM                     6.6.6.0/24
 -3  10.10.10.1       PIM    Wrong interface  6.6.6.0/24   
------------------------------------------------------------------


R1>mtrace 6.6.6.6 4.4.4.5 
Type Ctrl-C to abort.

Querying reverse path for source 6.6.6.6 to destination 4.4.4.5 via RPF
From source (?) to destination (?)

-----------------------------------------------------------------
|Hop|    OIF IP     |Proto| Forwarding Code |Source Network/Mask|
-----------------------------------------------------------------
  0  4.4.4.5          -->    Destination
 -1  4.4.4.4          PIM                     6.6.6.0/24        
 -2  20.20.20.2       PIM                     6.6.6.0/24
 -3  10.10.10.1       PIM    RPF Interface    6.6.6.0/24   
------------------------------------------------------------------

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