Creating VLANs in DD-WRT (Part 3)

In the second part of this post I completed the setup of VLANs on my WNR3500L router. To make them available to hosts (and VMs) I now have to configure my Cisco SLM2008 switches.

Fortunately that turns out to be fairly simple. The SLM 2008 has a web-based GUI that does the job nicely. Once logged in it’s a matter of opening the VLAN >> VLAN Settings page. Then just tap in the VLAN ID that you want to create and click “Add”.

This then drops you into an additional page where you choose which ports to associate the VLAN with. I picked all of the ports on this switch (where my ESX hosts are located). Then I clicked “Save”.

It’s just then a case of repeating for the other VLANs that are required. And that’s the switches done. The default configuration of them doesn’t require any further tweaking.

Within vSphere, the configuration required should be obvious. Here’s a screenshot from my ESX host with a portgroup called “Test” defined.

It has a VLAN ID of 6 and one VM in it with an IP Address of It can reach the router’s primary network, the internet and be contacted from my main network and wireless clients.

Exactly what I want for now.


Creating VLANs in DD-WRT (Part 2)

In the first part of this post I created some VLANs on my NetGear WNR3500L router that I’ve flashed with DD-WRT firmware. In this second part of the post I will be assigning IP address ranges to those VLANs and configuring the router’s firewall.

I want the VLANs that I setup previously to use separate IP Address ranges. To do this it’s back into to the telnet session and enter the following command:

[text]nvram set rc_startup=’
ifconfig vlan6 netmask
ifconfig vlan7 netmask
ifconfig vlan8 netmask
ifconfig vlan9 netmask
ifconfig vlan10 netmask
ifconfig vlan11 netmask
ifconfig vlan12 netmask
ifconfig vlan13 netmask
ifconfig vlan14 netmask
ifconfig vlan15 netmask

ifconfig vlan6 up
ifconfig vlan7 up
ifconfig vlan8 up
ifconfig vlan9 up
ifconfig vlan10 up
ifconfig vlan11 up
ifconfig vlan12 up
ifconfig vlan13 up
ifconfig vlan14 up
ifconfig vlan15 up

(There is actually a way to do this step through the router’s GUI too.)

Reboot the router again for the changes to take effect.

The final configuration that needs to be made is to the internal firewall of the router. With all of these new interfaces created, we need to define some rules to permit (or deny) traffic between them.

Now I could have just turned the firewall off but that wouldn’t be a very good idea. Instead I modified the rules. For a single VLAN (VLAN 6 for example) the following commands were required:

[text]iptables -I INPUT -i vlan6 -j ACCEPT
iptables -I FORWARD -i vlan6 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan6 -o ppp0 -m state –state NEW -j ACCEPT[/text]

The first line allows traffic from VLAN6 to talk to the router. The second line allows VLAN6 to talk to the default LAN network (VLAN1). The final line allows VLAN6 to access the WAN interface (internet).

There are two ways of applying these rules. The first is by executing the following on the router’s telnet interface:

[text]nvram set rc_firewall=’
iptables -I INPUT -i vlan6 -j ACCEPT
iptables -I FORWARD -i vlan6 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan6 -o ppp0 -m state –state NEW -j ACCEPT'[/text]

The other method is to use the GUI. Under Administration >> Commands there is a text are to enter the commands. Then all you need to do is click the “Save Firewall” button to have the commands take effect at the next reboot of the router. Additionally you can click the “Run Commands” button to execute them immediately. (Bear in mind though that commands run immediately are not persistent across a reboot.)

I thought that would sort everything out so I made the same changes for all of the VLANs. However, when it came to using those VLANs I discovered that although the could “talk” to the internet and to wireless clients, they could not “talk” to each other. This meant a revision to the firewall rules that I set out above was required.

Whilst working out what I needed, I discovered that a wildcard character exists and that what I wanted to achieve could be done in just 4 lines:

[text]iptables -I INPUT -i vlan+ -j ACCEPT
iptables -I FORWARD -i vlan+ -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan+ -o vlan+ -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan+ -o ppp0 -m state –state NEW -j ACCEPT[/text]

Line 1 accepts input from any of the VLAN interfaces into the router.

Line 2 allows any traffic coming from the VLAN interfaces to access the bridge (this is connected to the RJ45 ports and the wireless)

Line 3 allows traffic to come from any VLAN and go to any VLAN (this was the rule I was missing the first time around)

Line 4 allows traffic coming from any of the VLANs to go to the internet.

However, a quick word on the internet (WAN) interface, ppp0, and security in general. The WNR3500L router does not have an ADSL modem in it. (I have a separate one of those (Draytek Vigor 120)). Configuration of the WAN for my environment is therefore completed using the PPPoE protocol and hence the WAN interface gets called ppp0. If you use this router with cable broadband (e.g. Virgin Media) you may end up with a different WAN interface name. Not only will you have to adjust the rules above accordingly, you need to make sure that you don’t inadvertently open up a gaping security hole!

Which is why it might be best to stick the following rules into the router instead of the ones above:

[text]iptables -I INPUT -i vlan6 -j ACCEPT
iptables -I FORWARD -i vlan6 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan6 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan6 -o ppp0 -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan7 -j ACCEPT
iptables -I FORWARD -i vlan7 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan7 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan8 -j ACCEPT
iptables -I FORWARD -i vlan8 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan8 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan9 -j ACCEPT
iptables -I FORWARD -i vlan9 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan9 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan10 -j ACCEPT
iptables -I FORWARD -i vlan10 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan10 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan11 -j ACCEPT
iptables -I FORWARD -i vlan11 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan11 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan12 -j ACCEPT
iptables -I FORWARD -i vlan12 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan12 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan13 -j ACCEPT
iptables -I FORWARD -i vlan13 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan13 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan14 -j ACCEPT
iptables -I FORWARD -i vlan14 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan14 -o vlan+ -m state –state NEW -j ACCEPT
iptables -I INPUT -i vlan15 -j ACCEPT
iptables -I FORWARD -i vlan15 -o br0 -m state –state NEW -j ACCEPT
iptables -I FORWARD -i vlan15 -o vlan+ -m state –state NEW -j ACCEPT[/text]

Whilst it’s not as elegant a solution as the one with the wildcards, it is more specific and hence more secure and I’m not an iptables expert so I’m going for the safer option. Also note that in the above example, I’ve only given VLAN6 access to the ppp0 (internet / WAN) interface.

That’s just the simple firewall changes that can be made. More complex setups can be achieved but you need to know what you’re doing. There’s an introduction to IPTABLES that can be found on the DD-WRT site.

That’s it for the router’s configuration. In the third and final part of the post I describe how the VLANs are defined on the Cisco SLM2008 switches that I have connected to the router.


Creating VLANs in DD-WRT (Part 1)

I’m breaking this post up into 3 parts because it does go on a bit.

  • Part 1 – An overview of what I’m trying to do and creating VLANs on the router
  • Part 2 – Configuring IP ranges and the router’s firewall
  • Part 3 – Configuring VLANs on the SLM2008 switches

Recently I have flashed my home router (a NetGear WNR3500L) with DD-WRT firmware and performed some basic and intermediate configuration to connect it to the internet and direct DNS queries for my lab domain to the correct DNS server.

Now though I want to setup some VLANs. I want to be able to make use of some of the more advanced networking features in vSphere in my lab and this was one of the primary drivers for me selecting the router that I did.

I already have two Cisco SLM2008 smart switches in my lab. They are 8-port network switches that provide a number of useful features for the price. Simon Seagrave has a good description and review of the switches on his site, SLM2008 review. Upgrading and configuring my router to make better use of those features is what this post is about.

The standard DD-WRT interface allows you to assign single VLANs to individual ports but I want to go a step further than that and create 802.1q trunk ports. DD-WRT is capable of doing this but the configuration isn’t a point-and-click affair in the present build (so I understand).

Firstly, it might help to show the network topology that I’m aiming for here:

The rear of the NetGear router then looks like this:

The goal here is to create a small number of VLANs on the router and enable the two ports connected to the SLM2008 switches to carry 802.1q tagged packets. To do this we have to access the router via a telnet connection.

Enabling telnet on the router is fairly straightforward. On the Administration >> Management page, under Remote Access, it is simply a matter of enabling Telnet Management.

With that done you can use your favourite command line or terminal program to telnet to the router:

It’s worth noting that you have to login as “root” regardless of what you set the router’s username to be. The password will be whatever you set it to though.

The remainder of this article is based on the Switched Ports WIKI page on the DD-WRT site.

The first step is to examine the default VLAN configuration settings that are stored in NVRAM before we change them.

[text]nvram show | grep vlan.*ports[/text]

On the model of router that I’m using (WNR3500L in case you’d forgotten) you should get the following back:

[text]vlan2ports=0 8
vlan1ports=4 3 2 1 8*[/text]

(The results that you get back might vary if you have a different router.)

What this shows is that there are two VLANs in use by default. VLAN2 is assigned to the WAN port (port 0) and the internal CPU port (port 8). VLAN1 is assigned to all four LAN ports and the internal CPU port. The asterisk denotes that this is the default VLAN.

You’ll also want to run this command:

[text]nvram show | grep port.*vlans[/text]

That will return the following default settings:

[text]port5vlans=1 2 16

This shows that the LAN ports (1-4) are joined to VLAN1, the WAN port (0) is joined to VLAN2 and the internal CPU port (5 now and not 8 for some bizarre reason) is joined to VLANs 1 and 2 and is also Tagged (that’s what the 16 means).

And also this one:

[text]nvram show | grep vlan.*hwname[/text]



Some of these settings might need some further explaining. The switched ports page on the DD-WRT WIKI explains them fairly well.

In order to configure / change these settings though we need to “set” them and not just “show” them.

[text]nvram set vlan6ports="2t 1t 8"
nvram set vlan7ports="2t 1t 8"
nvram set vlan8ports="2t 1t 8"
nvram set vlan9ports="2t 1t 8"
nvram set vlan10ports="2t 1t 8"
nvram set vlan11ports="2t 1t 8"
nvram set vlan12ports="2t 1t 8"
nvram set vlan13ports="2t 1t 8"
nvram set vlan14ports="2t 1t 8"
nvram set vlan15ports="2t 1t 8"[/text]

These lines associate the VLANs 6 to 15 with ports 1 and 2 (as well as the internal CPU port) and, more importantly, adds the VLAN tags to packets on these ports.

[text]nvram set port1vlans="1 6 7 8 9 10 11 12 13 14 15 16"
nvram set port2vlans="1 6 7 8 9 10 11 12 13 14 15 16"
nvram set port5vlans="1 2 6 7 8 9 10 11 12 13 14 15 16"[/text]

These lines associate all of the VLANs (except VLAN2 – the WAN) with ports 1 and 2. All VLANS (including the WAN) are associated with the internal CPU port. All three ports are tagged.

[text]nvram set vlan6hwname=et0
nvram set vlan7hwname=et0
nvram set vlan8hwname=et0
nvram set vlan9hwname=et0
nvram set vlan10hwname=et0
nvram set vlan11hwname=et0
nvram set vlan12hwname=et0
nvram set vlan13hwname=et0
nvram set vlan14hwname=et0
nvram set vlan15hwname=et0[/text]

These lines simply associate the VLANs with the right hardware.

[text]nvram commit

Finally the changes are committed and the router rebooted.

(Note that unless specifically overwritten, the original settings that we saw earlier will remain in force. So ports 3 and 4 remain unchanged from their original configuration.)

In summary, what the commands above did is:

  • Created VLANs 6 to 15 inclusive
  • Tagged VLANs 1 and 6 to 15 on ports 1, 2 and 8 (the internal CPU port)

(I expected at that point to lose contact with my lab servers but it didn’t happen. It seems that DD-WRT enumerates the port numbers in reverse order to how they are labelled on the router. So the commands that I entered actually ran on ports 3 and 4! This I verified by re-patching my cables and losing connectivity.)

In the second part of this post I’m going to assign address ranges to my VLANs and configure the router’s firewall.