Switching in software on Linux is one of the important parts when using virtualization technologies like KVM or LXC. Typical hosts do not provide one or more physical adapters for each NIC of a virtual machine in KVM or per container when using LXC. Something else must take the part to interconnect the virtual network interfaces.
The software switching classical tool is the linuxbridge, which is available in the Linux kernel for a long time. The frontend to manage the linuxbridge isbrctl. The newer tool is the Openvswitch (athttp://openvswitch.org/). The main frontend isovs-vsctl.
In this post I will show multiple solutions to interconnect Linux namespaces using a software based switch. A performance analysis of these solutions will be discussed in another article later. Starting with network namespaces helps to understand the more complex situations when using KVM or LXC.
tap interfaces
Linux tap interfaces created with ip tuntap cannot be used to attach network namespaces to linuxbridges or the openvswitch.
veth pair
The simple solution to connect two network namespaces is the usage of one veth pair. This has been discussed in a previous artice.
Connecting namespaces using a veth pair
The command sequence has been discussed in a previous article, but we show the commands here again
veth pair
# add the namespaces
ipnetnsaddns1
ipnetnsaddns2
# create the veth pair
iplinkaddtap1typevethpeernametap2
# move the interfaces to the namespaces
iplinksettap1netnsns1
iplinksettap2netnsns2
# bring up the links
ipnetnsexecns1iplinksetdevtap1up
ipnetnsexecns2iplinksetdevtap2up
# now assign the ip addresses
linux bridge and two veth pairs
When more than two network namespaces (or KVM or LXC instances) must be connected a switch should be used. Linux offers as one solution the well known linux bridge.
Connecting namespaces using a linux bridge and two veth pairs
We need for this setup one switch, and two connectors. In this setup we use a linuxbridge and two veth pairs.
The commands to create this setup are:
linuxbridge and two veth pairs
# add the namespaces
ipnetnsaddns1
ipnetnsaddns2
# create the switch
BRIDGE=br-test
brctladdbr$BRIDGE
brctlstp$BRIDGEoff
iplinksetdev$BRIDGEup
#
#### PORT 1
# create a port pair
iplinkaddtap1typevethpeernamebr-tap1
# attach one side to linuxbridge
brctladdifbr-testbr-tap1
# attach the other side to namespace
iplinksettap1netnsns1
# set the ports to up
ipnetnsexecns1iplinksetdevtap1up
iplinksetdevbr-tap1up
#
#### PORT 2
# create a port pair
iplinkaddtap2typevethpeernamebr-tap2
# attach one side to linuxbridge
brctladdifbr-testbr-tap2
# attach the other side to namespace
iplinksettap2netnsns2
# set the ports to up
ipnetnsexecns2iplinksetdevtap2up
iplinksetdevbr-tap2up
#
openvswitch and two veth pairs
Another solution is to use the openvswitch instead of the „old“ linuxbrige. The configuration is nearly the same as for the linuxbridge.
Connecting namespaces using the openvswitch and two veth pairs
We need for this setup one switch, and two connectors. In this setup we use an openvswitch and two veth pairs.
The commands to create this setup are:
openvswitch and two veth pairs
# add the namespaces
ipnetnsaddns1
ipnetnsaddns2
# create the switch
BRIDGE=ovs-test
ovs-vsctladd-br$BRIDGE
#
#### PORT 1
# create a port pair
iplinkaddtap1typevethpeernameovs-tap1
# attach one side to ovs
ovs-vsctladd-port$BRIDGEovs-tap1
# attach the other side to namespace
iplinksettap1netnsns1
# set the ports to up
ipnetnsexecns1iplinksetdevtap1up
iplinksetdevovs-tap1up
#
#### PORT 2
# create a port pair
iplinkaddtap2typevethpeernameovs-tap2
# attach one side to ovs
ovs-vsctladd-port$BRIDGEovs-tap2
# attach the other side to namespace
iplinksettap2netnsns2
# set the ports to up
ipnetnsexecns2iplinksetdevtap2up
iplinksetdevovs-tap2up
#
openvswitch and two openvswitch ports
Another solution is to use the openvswitch and make use of the openvswitch internal ports. This avoids the usage of the veth pairs, which must be used in all other solutions.
Connecting namespaces using the openvswitch and two openvswitch ports
We need for this setup one switch, and two connectors. In this setup we use an openvswitch and two openvswitch ports.
The commands to create this setup are:
openvswitch and two openvswitch internal ports
# add the namespaces
ipnetnsaddns1
ipnetnsaddns2
# create the switch
BRIDGE=ovs-test
ovs-vsctladd-br$BRIDGE
#
#### PORT 1
# create an internal ovs port
ovs-vsctladd-port$BRIDGEtap1--setInterfacetap1type=internal
# attach it to namespace
iplinksettap1netnsns1
# set the ports to up
ipnetnsexecns1iplinksetdevtap1up
#
#### PORT 2
# create an internal ovs port
ovs-vsctladd-port$BRIDGEtap2--setInterfacetap2type=internal
# attach it to namespace
iplinksettap2netnsns2
# set the ports to up
ipnetnsexecns2iplinksetdevtap2up
Performance
In another article I will show some performance numbers for the four presented solutions. There are noticeable differences with respect to throughput and CPU usage.