Month: January 2010

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VLAN Tagging in Linux

Recently I have been doing some reworking on networking at work. One of the new requirements is that everything be network connection be a tagged VLAN. This is a pretty simple process in Red Hat Linux with multiple paths. Test files are my favorite way to make these changes so lets assume that I want the VLAN to be 455 with the nic eth0.

  • Navigate to your networking scripts:  /etc/sysconfig/network-scripts
  • Copy your current eth0 configuration cp ifcfg-eth0 ifcfg-eth0.455
  • Open the file:
DEVICE=eth0
IPADDR=192.168.10.10
NETMASK=255.255.255.0
BOOTPROTO=static
HWADDR=00:e0:4c:87:e2:36
MTU=1500
ONBOOT=yes
BROADCAST=192.168.10.255
NETWORK=192.168.10.0
DNS1=192.168.10.1
  • Modify the device name to read eth0.455
  • Add the line VLAN=yes to the end of the file
  • Save and exit
  • Shutdown the old interface (make sure your on console)
  • ifdown eth0
  • Bring up new VLAN
  • ifup eth0.455
  • Delete old interface rm ifcfg-eth0

That’s all you have to do and your Operating system will be tagging all outbound traffic with VLAN 455 and only reading traffic from 455.

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Mounting via labels in fstab

An issue I have run into on Solaris is the dreaded device rename during a reboot. This can wreak havoc on your system during booting making it unable to boot. This problem was addressed in multiple ways in Linux. One of the most common methods is via labels. This allows you to write a string name to the disk and mount the disk via the string name. I find this particularly useful when using hot swappable drives in my PC. To see the current label on a disk:

[root@linuxmonkey ~]# e2label /dev/sda1
/boot

so the label on disk /dev/sda1 is /boot

To set a label type
[root@linuxmonkey ~]# e2label /dev/sda1 label_name

In order to mount via label instead of the traditional /dev/sda1 in fstab use a

LABEL=/boot

And you have a mount that is not effected by reboots.