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Thread: Dot1q module

  1. #1
    Join Date
    Sep 2012
    Beans
    2

    Dot1q module

    I'm setting up a GNS3 lab at work on Ubuntu Server 12.04 x64. I have a few questions on how the dot1q module works along with the /etc/network/interfaces file.

    What I'm trying to accomplish:
    • The trunk interface and all it's sub interfaces (eth6) should not have an IP - just a layer 2 interface.
    • The interface i use for SSH (eth2) to connect to the box shouldn't be trunking.
    • The MTU on the trunk interface should be 1536. This gives me enough overhead to do qinq.


    The problem I'm having is that when using 'inet static' in /etc/network/interfaces it doesn't seem to like that I'm not specifying an IP address. Yes, I could always set this use a 127.0.0.8/8 address but I'm trying to keep it a layer 2 only interface if possible. Also, the MTU size doesn't seem to stick, but I'm pretty sure this is because it errors out when there is no ip assigned. As for the dot1q module, it is only loaded when I speficy a sub interface, correct? For example, I have an eth6.99 interface that should be trunking but I don't want eth2 to be doing so.

    /etc/network/interfaces
    Code:
    # The loopback network interface
    auto lo
    iface lo inet loopback
    
    # The primary network interface
    auto eth2
    iface eth2 inet dhcp
    
    #Trunk interface to Lab Switches
    auto eth6
    iface eth6 inet static
    mtu 1536
    
    #VLAN 99 on eth6
    auto eth6.99
    iface eth6.99 inet static
    mtu 1536
    /etc/modules
    Code:
    #/etc/modules: kernel modules to load at boot time.
    #
    # This file contains the names of kernel modules that should be loaded
    # at boot time, one per line. Lines beginning with "#" are ignored.
    loop
    lp
    rtc
    #Load 802.1q module for breakout switch
    8021q

  2. #2
    Join Date
    Sep 2012
    Beans
    2

    Re: Dot1q module

    I found the answer.

    I was right that when using 'static' in /etc/network/interfaces you MUST specify an IP address. The trick is to set it to 'manual'

    /etc/network/interfaces
    Code:
    # The primary network interface
    auto eth2
    iface eth2 inet dhcp
    
    #dot1q interface
    auto eth6
    iface eth6 inet manual
    What I needed to do was add another script to do the heavy lifting for all my sub interfaces attached to eth6.

    /home/nuul/GNS3/VLANup.sh (this has to be run with elevated privileges obviously)
    Code:
    # Bring up the physical interface
    ifconfig eth6 up
    ifconfig eth6 mtu 7000
    
    # Add subs
    ip link add link eth6 name eth6.101 type vlan id 101
    ip link add link eth6 name eth6.102 type vlan id 102
    
    # Bring up subs
    ifconfig eth6.101 up
    ifconfig eth6.102 up
    
    # Set MTU on subs
    ifconfig eth6.101 mtu 1536
    ifconfig eth6.102 mtu 1536

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