VLAN Support in Linux
The typical configuration of a Linux box as a firewall/gateway is to have two physical interfaces, with one connected to the Internet router (public side) and the other connected to the internal LAN switch (private side), as shown in Figure 3.
But, what if the Internet router and switch/patch panel are inside a wiring closet where there is no room to install a Linux box, and every possible location to put it has only a single jack/cable?
VLANs make this no problem. Instead of installing the Linux box physically in between the public and private networks, you can install a small off-the-shelf VLAN switch, configured with two VLANs (VIDs 1 and 2).
Configure one port as a member of both VLANs with Tagging on. You'll plug the Linux box in to this port. This should be the only port configured with Tagging, because it's the only port that will talk to another VLAN device (the Linux box). Every other port will be set to Untagged.
Configure another port of the switch as a member of VLAN 2 only (Untagged, PVID set to 2). You'll plug the Internet router in to this port.
Leave the rest of the ports on VLAN 1 only (Untagged, PVID set to 1). These are the ports for all the hosts on the private network. If there are more hosts than ports, you can plug in another switch or switches (non-VLAN) to any of these VLAN 1 ports to service the rest of the hosts.
The Linux box needs only one physical interface (eth0). Run these commands to configure the VLANs:
ip link set eth0 up vconfig add eth0 1 ip link set eth0.1 up vconfig add eth0 2 ip link set eth0.2 up
Just like in the first example, you now would configure your IP addresses and firewall normally, using eth0.1 as the interface on the private network and eth0.2 as the interface on the public network (Figure 4).
As in the first example, because there is only one physical interface in the Linux box, there is no need to define a bridge.
The VLAN switch ports in this example are acting like interfaces of the Linux box. You easily can extend this concept for other applications and scenarios. Using a 24-port VLAN switch, you could have the equivalent of 23 Ethernet interfaces in a Linux box if you created 23 separate VLANs. The 24th port would be used to connect the Linux box to the switch and would need to Tag all the packets for the 23 VLANs.
You can use tcpdump to see Tagged and Untagged packets on the wire and to make sure traffic is showing up on the expected interfaces. Use the -e option to view the Ethernet header info (which shows 802.1Q Tags) and the -i option to sniff on a specific interface. For example, run this command to show traffic for VLAN 10:
tcpdump -e -i eth0.10
You should see normal traffic without VLAN Tags. If VLAN 10 contains more than a few hosts, you should at least start seeing ARP and other normal broadcast packets (like any switched network, you won't see unicast packets not addressed to your host/bridge).
If the eth0.10 VLAN interface is working correctly above, you should see the Tagged 802.1Q packets if you look at the traffic on the underlying physical interface, eth0:
tcpdump -e -i eth0
If you run this command at the same time as the eth0.10 capture, you should see the Tagged version of the same packets (as well as packets for any other VLAN interfaces set up on eth0).
802.1Q VLAN Implementation for Linux (vlan package): www.candelatech.com/~greear/vlan.html
IEEE 802.1Q-2005—Virtual Bridged Local Area Networks: standards.ieee.org/getieee802/download/802.1Q-2005.pdf
IEEE 802.1D-2004—Media Access Control (MAC) Bridges: standards.ieee.org/getieee802/download/802.1D-2004.pdf
Henry Van Styn is the founder of IntelliTree Solutions, an IT consulting and software development firm located in Cincinnati, Ohio. Henry has been developing software and solutions for more than ten years, ranging from sophisticated Web applications to low-level network and system utilities. He is the author of Strong Branch Linux, an in-house server distribution based on Gentoo. Henry can be contacted at www.intellitree.com.
Fast/Flexible Linux OS Recovery
On Demand Now
In this live one-hour webinar, learn how to enhance your existing backup strategies for complete disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible full-system recovery solution for UNIX and Linux systems.
Join Linux Journal's Shawn Powers and David Huffman, President/CEO, Storix, Inc.
Free to Linux Journal readers.Register Now!
|Working with Command Arguments||May 28, 2016|
|Secure Desktops with Qubes: Installation||May 28, 2016|
|CentOS 6.8 Released||May 27, 2016|
|Secure Desktops with Qubes: Introduction||May 27, 2016|
|Chris Birchall's Re-Engineering Legacy Software (Manning Publications)||May 26, 2016|
|ServersCheck's Thermal Imaging Camera Sensor||May 25, 2016|
- Secure Desktops with Qubes: Introduction
- Secure Desktops with Qubes: Installation
- Download "Linux Management with Red Hat Satellite: Measuring Business Impact and ROI"
- CentOS 6.8 Released
- The Italian Army Switches to LibreOffice
- Linux Mint 18
- Working with Command Arguments
- ServersCheck's Thermal Imaging Camera Sensor
- Chris Birchall's Re-Engineering Legacy Software (Manning Publications)
- Petros Koutoupis' RapidDisk
Until recently, IBM’s Power Platform was looked upon as being the system that hosted IBM’s flavor of UNIX and proprietary operating system called IBM i. These servers often are found in medium-size businesses running ERP, CRM and financials for on-premise customers. By enabling the Power platform to run the Linux OS, IBM now has positioned Power to be the platform of choice for those already running Linux that are facing scalability issues, especially customers looking at analytics, big data or cloud computing.
￼Running Linux on IBM’s Power hardware offers some obvious benefits, including improved processing speed and memory bandwidth, inherent security, and simpler deployment and management. But if you look beyond the impressive architecture, you’ll also find an open ecosystem that has given rise to a strong, innovative community, as well as an inventory of system and network management applications that really help leverage the benefits offered by running Linux on Power.Get the Guide