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Old 07-19-2014, 05:29 AM   #1
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Registered: Jun 2011
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Bridge filters DHCP traffic

On a virtualization host system I have created a bridge (using NetworkManager) for a bunch of VMs.

VM1 is a DHCPv4 and DHCPv6 server with static IPv4/IPv6.
VM2 is supposed to receive it's IPv4 and IPv6 addresses from that server.

When using tcpdump on the bridge from the host system, I can see VM2 sending DHCP requests.
When using tcpdump on VM1, nothing comes in.

The host system has all policies set to accept in ebtables.
The VM1 system has its firewall disabled.

I'm missing something really obvious as this happens on multiple Linux distributions and regardless of whether I use NetworkManager or command line brctl to set up the bridge. Why is the bridge not forwarding DHCP traffic?

Last edited by hooba; 07-19-2014 at 05:35 AM.
Old 07-21-2014, 07:54 AM   #2
Registered: Feb 2008
Distribution: Fedora,RHEL,Ubuntu
Posts: 661

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Does the host system traffic reaching to VM1? Also verify MAC address of VMs which must be unique.

Old 07-21-2014, 08:00 AM   #3
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Registered: Jun 2011
Posts: 3

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The host system can communicate with the VMs and their MAC is all different.

While I was verifying this I noticed that DHCP started working after I cleared iptables on the host. Apparently broadcast traffic on the bridge was blocked through iptables.


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