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Category: Network

Fixing strange device names using Ubuntu templates on VMware ESX or vSphere

If you regularly deploy Ubuntu VM templates on your VMware ESX(i) or VMware vSphere boxes you will probably run into strange network device numbers. This is caused by a udev rule. This problem has been confirmed to exist in Ubuntu 9.04, 9.10 and 10.04. I haven’t had the time to check out other versions of Ubuntu. It’s also still existing in RHEL 6 and Scientific Linux 6.

As you can see below we have two ethernet devices: eth4 and eth5 instead of the usual eth0
and eth1.

root@box:~# ifconfig | grep Link
lo        Link encap:Local Loopback  
eth4  Link encap:UNSPEC  HWaddr  
eth5  Link encap:UNSPEC  HWaddr  

Lucky for us it’s very simple to persistenly assign the correct device names to the corresponding mac address.

root@box:~# grep eth4 /etc/udev/rules.d/70-persistent-net.rules 
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", 
ATTR{address}=="00:11:22:33:44:55", ATTR{dev_id}=="0x0", 
ATTR{type}=="1", KERNEL=="eth*", NAME="eth4"

Use your favorite editor to edit /etc/udev/rules.d/70-persistent-net.rules.
Replace NAME=”eth4″ with NAME=”eth0″ and do the same with eth5.
Save the config file, reboot and you’re done!

After writing this guide I’ve also found this issue to exist on other udev-based distro’s (e.g. OpenSUSE) and other VMware products too (e.g. Fusion and Workstation). The same fix applies, so no worries there.

Using expect scripts to backup your Cisco configuration

In this short howto I’ll explain how to use expect scripts with Cisco devices. In this example I’m going to use it to backup the current running configuration.


  • A working tftp server
  • Expect
  • Lucky for us both requirements are available in all major distro’s.

    The Debian/Ubuntu way:

    sudo apt-get install tftp tftpd expect

    Next on our todo list is configuring the tftp server. This should also be fairly easy:

    # cat /etc/xinetd.d/tftp
    service tftp
        protocol        = udp
        port            = 69
        socket_type     = dgram
        wait            = yes
        user            = nobody
        server          = /usr/sbin/in.tftpd
        server_args     = /tftpboot
        disable         = no

    Restart your xinetd server when done.

    # /etc/init.d/xinetd restart

    Make sure the /tftpboot folder exists and is owned by user and group nobody:

    # chown -R nobody:nobody /tftpboot

    You should also create an empty file where you’d like to save your configuration and rerun the above command to adjust permissions.

    # touch /tftpboot/config
    # chown -R nobody:nobody /tftpboot

    You should also create an empty file where you’d like to save your configuration and rerun the above command to adjust permissions.

    # touch /tftpboot/config
    # chown -R nobody:nobody /tftpboot

    We can now test our newly configured tftpd server:
    Create a new file in your home dir called config and put some random text in it.

    # cat /home/user/config
    test 12
    # tftp
    tftp> open localhost
    tftp> put config
    Sent 146 bytes in 0.0 seconds
    # cat /tftpboot/config
    test 12

    Excellent! We’re ready to receive config files from the Cisco device.

    Below you will find an example script:

    ## TomDV
    # ---------------- configuration ---------------- #
    set device    # cisco device
    set tftp      # tftp server
    set user someuser           # username
    set pass ultrasecret        # password
    set config                  # config destination
    set timeout 60
    # -------------- do not edit below -------------- #
    spawn telnet $device
    expect "Password:"
    send "$pass\n"
    expect ">"
    send "en\n"
    expect "Password:"
    send "$pass\n"
    send "copy running-config tftp://$tftp/$config\n\n"
    expect "$tftp"
    send "\n"
    expect "$config"
    send "\n"
    send "exit\n"

    Save it anywhere you like and run it from the shell. You’ll see something like this in your logs:

    user in.tftpd[22304]: connect from (
    user tftpd[22305]: tftpd: trying to get file: config
    user tftpd[22305]: tftpd: serving file from /tftpboot

    That’s it. Your current Cisco config has been saved to /tftpboot/config.

    I wouldn’t recommend using this into production without proper firewalling. You can get the same results by using snmp. But that’s however a subject for another howto.