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New Contributor II

KVM Bridges, Multicast Traffic, and Traffic Explosions!

Hello all!

I have a strange issue I wanted to get some opinions on.  I have some KVM hosts with bridge interfaces configured that connect to a NetVanta 1544.  Most of these hosts are configured as trunk ports since KVM guests need to be able to reach the various networks configured on the switch. Each KVM host is configured identically to all the others in the network.  On the KVM host in question when I set my trunk port on the Adtran, and set the native VLAN multicast traffic goes crazy. After a few minutes random hosts within various VLANs start dropping, and are unable to ping their gateways (the L3 in this case).  This does not happen to all the hosts, just a random few.  I find this very strange.  I have disabled STP on the bridge interface, checked ARP, and do not see anything wrong on the KVM host side.

When I set the port to an access port everything works perfectly fine. There is only one other VLAN configured on the KVM host, but that really should not matter. When I TCPDUMP the br0 interface on the KVM host I do not see anything out of the ordinary.


interface gigabit-switchport 0/18

  description KVM LAB

  spanning-tree edgeport

  no shutdown

  switchport trunk vlan 80

  switchport trunk native vlan 80

giga-swx 0/18 is UP, line protocol is UP

  Description: KVM LAB

  Hardware address is 00:A0:C8:44:67:36

  RJ-45 Shielded

  1Gb/s, negotiated full-duplex, configured full-duplex

  input flow control is disabled, 0 pause frames received

  ARP type: ARPA; ARP timeout is 20 minutes

  Last clearing of "show interface" counters: never

  30 second input rate 6848 bits/sec, 8 packets/sec

  30 second output rate 6840 bits/sec, 8 packets/sec

    2 total jumbo frames

    78894 packets input, 21249824 bytes

    48497 unicasts, 7672 broadcasts, 22725 multicasts input

    0 unknown protocol, 84 discards

    0 input errors, 0 runts, 0 giants

    0 alignment errors, 0 crc errors

    3436861 packets output, 317186411 bytes

    294544 unicasts, 1931717 broadcasts, 1210600 multicasts output

    0 output errors, 0 deferred, 379 discards

    0 single, 0 multiple, 0 late collisions

    0 excessive collisions

Thank you!

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4 Replies
Not applicable

Re: KVM Bridges, Multicast Traffic, and Traffic Explosions!


Thank you for asking this question in the support community.  At this point, I will need a little more information to assist you further.  Is it possible you could reply to this post and attach the ADTRAN's configuration (please, remember to remove any information that may be sensitive to the organization), as well as any additional information you have about the network topology and design?

The configuration snippet you posted does not show the port as a trunk port, because it isn't configured with the switchport mode trunk command.  Based on the input/output you showed, there is a lot of broadcasts as well, so again, I'd like to see the rest of the configuration and understand the how the network is designed to work.


Not applicable

Re: KVM Bridges, Multicast Traffic, and Traffic Explosions!


I went ahead and flagged this post as "Assumed Answered." If any of the responses on this thread assisted you, please mark them as Correct or Helpful as the case may be with the applicable buttons. This will make them visible and help other members of the community find solutions more easily. If you still need assistance, we would be more than happy to continue working with you on this - just let us know in a reply.



Not applicable

Re: KVM Bridges, Multicast Traffic, and Traffic Explosions!


What was the answer?  We have a similar issue with a KVM setup.  lots of multicast output.



New Contributor II

Re: KVM Bridges, Multicast Traffic, and Traffic Explosions!

There really wasn't one.  After enganging AdTran support, they were under the impression it was the KVM host causing the issue. However, support was not able to explain why the identical setup was working with other bridged interfaces. As for the Linux side, I tried a variety of things.  From tweaking the bridge interface, to rate limits, to STP adjustments, to Kernel sysctls. The firmware was one release behind on the AdTran 1544, I have since upgraded, and have not tried again using a trunk port.  Right now its an access port.

It was noted to me that there were a couple of bugs in the firmware that *could* potentially effect multicast in the firmware i was running. its about time to try this again.  What specifically is your setup, and how are your bridge interfaces configured?