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labradort
Asked: 2014-07-17 06:38:53 +0800 CST

KVM virtualization with two bridges, want routing to use each bridge as mapped in KVM

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I can't seem to find an existing question like my scenario. I'm using 2 public bridges for 4 VMs. Two VMs per bridge device. Interface stats show there is use of the assigned bridge for the VM on inbound traffic, but outbound is going through only the first bridge.

# cat /etc/network/interfaces 

# The loopback network interface
auto lo
iface lo inet loopback

pre-up iptables-restore < /etc/firewall-rules

auto br0
iface br0 inet dhcp
    bridge_ports    eth0
    bridge_stp      off
    bridge_maxwait  0
    bridge_fd       0

auto br1
iface br1 inet dhcp
    bridge_ports    eth1
    bridge_stp      off
    bridge_maxwait  0
    bridge_fd       0


#  brctl show
bridge name     bridge id               STP enabled     interfaces
br0             8000.a4badb4e3949       no              eth0
                                                        vnet0
                                                        vnet2
br1             8000.a4badb4e394a       no              eth1
                                                        vnet1
                                                        vnet3
# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         vlan-200.mydoma 0.0.0.0         UG    0      0        0 br0
XXX.YYY.200.0   *               255.255.248.0   U     0      0        0 br0
XXX.YYY.200.0   *               255.255.248.0   U     0      0        0 br1

The routing makes sense with what I'm seeing: all outbound traffic, unless for the 200 subnet, will use br0.

How can it be configured so that the KVM guests on br1 have their outbound traffic truly use br1 for their gateway? The current set up works fine, but I'd prefer to assign the bridges to VMs as their own full gateway so br1 is better utilized for TX packets.

linux

1 Answers

  1. Best Answer

    If the interfaces are on the same subnet, bond them. If they're not, unless the VMs have routes that traverse the second bridge, they're never going to use it. It looks like they are on the same subnet, in which case, follow this guide:

    https://wiki.debian.org/Bonding

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