Description

This article provides steps to troubleshoot the L2 multicast not working on the same vlan.
Consider the following topology

Src-------------ge-0/0/0-EX4300--ge-0/0/1-------------Downstream

Both ge-0/0/0 and ge-0/0/1 are in the same vlan.

{master:0}
labroot@EX43K> show vlans

Routing instance        VLAN name             Tag          Interfaces


default-switch          VLAN1360              1360
                                                           ge-0/0/0.0*
                                                           ge-0/0/1.0*

labroot@EX43K> moniter interface traffic

Interface    Link  Input packets        (pps)     Output packets        (pps)
 ge-0/0/0      Up      273892216       (1000)           155783          (1)
 ge-0/0/1      Up           2194          (0)           155802          (1)

 

Symptoms

When the traffic is send from the Src on ge-0/0/0 the traffic is seen on the interface incoming but it is not forwarded towards the ge-0/0/1 interface.
The interface ge-0/0/0 on which the multicast traffic is received is configured as a untagged port and it is part of vlan 1360.
On checking the interface statistics of ge-0/0/0 we can see the following 

MAC statistics:                      Receive         Transmit
 Total octets                      35998500             1167
 Total packets                        23999               13
 Unicast packets                          0                0
 Broadcast packets                        0                0
 Multicast packets                    23999               13
 CRC/Align errors                         0                0
 FIFO errors                              0                0
 MAC control frames                       0                0
 MAC pause frames                         0                0
 Oversized frames                         0
 Jabber frames                            0
 Fragment frames                          0
 VLAN tagged frames                   24000   >>>>>>>>>> vlan tagged frames received on the interface
 Code violations                          0

Since the tagged frames with wrong vlan tag were received on the ge-0/0/0 , the packets were dropped on ge-0/0/0 and not forwarded/flooded to ge-0/0/1.

Solution

So in these cases the solution would be to either remove the vlan tag from the source traffic or correct the vlan tag on the incoming packets so that it is processed correctly and forwarded to the downstream interfaces.

Modification History

2024-03-13 : Article Created