Thursday, May 5, 2011

802.1q and LACP Network Card Bonding with Xen Dom0

​As you may/may not know, bonding is the ability of taking two or more network cards and make them act as one. This not only improves fail over, but it also increases the amount of network throughput for the server. The following will show you how to set up such an environment. For this to work you must have a switch that is capable of combining multiple switch ports together. This can be done on either a single switch (which is still a single point of failure) or a switch that is stackable such as Cisco’s 3750 line of products.
There are six different kinds of NIC bonding in Linux, the one we will set up is mode 4 which follows the 802.3ad standard known as link aggregate control protocol. This allows for an active-active grouping of network cards and in testing resulted in zero ping drop, though I did see a momentary spike in response time (from 2ms to 20-30ms during convergence).
    First you need to check that your network card is capable of 802.1q VLAN tagging. You will need to research the capabilities of the card to make sure. Run ‘lspci | grep -i ethernet’ and note the response.
    Second, check to see if the 802.1q module is installed by running ‘lsmod | grep 8021q’.  If its not installed then run ‘yum install bridge-utils’
    Once those steps are done we can start configuring the network cards.  Go to /etc/sysconfig/network-scripts, in there you should see your network card configuration files; usually named ‘ifcfg-eth#’.  Write down or make a backup copy of the network information in your active NIC configuration file as you will need it later.
    Edit your first configuration file with the following
        DEVICE=eth0
        ONBOOT=yes
        BOOTPROTO=none
        USERCTL=no
        MASTER=bond0
        SLAVE=yes
    Your secondary card will contain the same information however the ‘DEVICE=eth#’ should match the name of the second card.
    Next we card the bonded interface, which then becomes the main device for the server. Create a new file named ‘ifcfg-bond0′:
        DEVICE=bond0
        BOOTPROTO=none
        ONBOOT=yes
        TYPE=Ethernet
        USERCTL=no
    We now create the configuration file which will handle the 802.1q jumbo frames. Note that the device is named ‘bond0.17′. This is important as the ’17′ is the VLAN ID which the server will listen on. Make sure you know which VLAN’s are in your environment! Create a file named ‘ifcfg-bond0.17′:
        DEVICE=bond0.17
        BOOTPROTO=static
        ONBOOT=yes
        VLAN=yes
        TYPE=Ethernet
        BRIDGE=xenbr17
   
    The ‘BRIDGE’ string is also important as this will tie the bond0.17 config file to the Xen bridge we are about to create. Repeat that step for every VLAN that you want your server to listen to.
    Next we will create the configuration file that the DomU will be given. Create a file called ‘ifcfg-xenbr17′ and place the following:
        DEVICE=xenbr17
        TYPE=Bridge
        BOOTPROTO=static
        ONBOOT=yes
        DELAY=0
        STP=off
   
    We will now create the management interface for the server. The management interface should have the same security restrictions as a management interface would have for a switch or any other network device. If someone compromises your Dom0, then all of your DomU’s are also compromised. ACL’s should be implemented for this network!
        DEVICE=xenbr192
        TYPE=Bridge
        BOOTPROTO=static
        ONBOOT=yes
        DELAY=0
        STP=off
        IPADDR=192.168.1.12
        NETMASK=255.255.255.0
        NETWORK=192.168.1.0
        BROADCAST=192.168.1.255
   
    Edit the /etc/modprobe.conf file and append the following:
        alias bond0 bonding
        options bond0 miimon=100 mode=4 lacp_rate=1
   
    That told the server what type of network bonding we will use. ‘mode=4′ tells the server that we want to use 802.3ad as our protocol for communication to the switch device.
    Edit the /etc/xen/xend-config.sxp file, change where it says ‘(network-script network-bridge)’ to ‘(network-script ‘network-bridge-bonding bridge=bond0 netdev=0′)’
    Now reboot the server
The next steps we will configure a Cisco switch, create the port channel, and configure it for LACP with 802.1q trunking.
    Log into your switch, go to the global configuration mode and create a port channel interface by typing ‘int port-c 1′
    Enter the following:
        switchport trunk encapsulation dot1q
        switchport mode trunk
   
    Now go to the actual switch interfaces and enter the following:
        switchport trunk encapsulation dot1q
        switchport mode trunk
        channel-group 1 mode active
   
    If the switch ports had originally been set up as an access interface, you can remove the configuration by entering:
        no switchport mode access
        no switchport access vlan VLAN ID
   
    Now save the configuration file
Installation of new DomU’s will be the same as before by giving them a ‘xenbr#’ interface