[HOWTO] VLANs in a Snap with Gentoo

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

I've been meaning to figure this out, so today I did and it's so easy I thought I'd post a guide so people don't put it off like I did thinking it complicated.

First, let me explain the differences between the Linux and Cisco implementations of 802.1q. 802.1q is the standards-based trunking protocol, meaning it allows the carrying of multiple VLANs. Cisco has another protocol that they used first, but most devices can use both. Being OSS fans, we like the standards so we'll stick with 802.1q.

Cisco uses one port to communicate with all VLANs in an 802.1q trunk. Linux splits this task, one VLAN per virtual NIC. Gentoo will setup these Virtual NICs for you once you tell it what to expect.

Assumptions
I'm assuming that your switches already have VLANs setup and that you simply want to add Linux to the mix. I also assume that your using the cisco port FastEthernet 0/1, that your linux box is using eth1 for this exercise and that you have 3 vlans setup on the Cisco device with the IDs, 1 2 3.

Cisco VLAN Setup

Setup the Cisco port for an 802.1q trunk first if that is what is on the other end. If a Linux device, just do the Linux side twice. If you have a different VLAN capable device, you'll have to consult your vendor's documentation and get back to us with a comment here to tell us how to do it.

For the 2900XL, Log into the IOS and type the following commands:

Strenuus · n00b Joined: 27 Jan 2004 Posts: 26 Location: Texas

Thank you so much flickerfly, I too have been putting this off for a while now and didn't think it would have been that simple. Thank you for the simpe howto.

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

My pleasure, I figured there had to be at least one other person out there waiting for this.
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Strenuus · n00b Joined: 27 Jan 2004 Posts: 26 Location: Texas

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

Apparently the Linux CDP project died due to lack of interest. I hear that Ethreal supports the sniffing of CDP though. I haven't played with that yet.
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UberLord

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

What is the benefit of the new ones? I don't see any change outside the variable name. What do I gain?
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ali3nx · Posted: Sat Oct 30, 2004 7:18 am Post subject:

nice

I'll be making use of this in short order at the isp i work for! Thanks
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UberLord · Posted: Sat Oct 30, 2004 11:09 am Post subject:

GentooBox · Veteran Joined: 22 Jun 2003 Posts: 1168 Location: Denmark

what ! is there a CDP for linux ?

thats awsome.

nice guide BTW.
and thanks for useing dot1q instead of ISL.

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

Thanks to UberLord and GentooBox for providing improvements to the original guide. I've integrated your additions above.
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flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

UberLord

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

UberLord

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

I'm going to need a quick tutorial on unmanking that package. I know how to do it the old way, but haven't fully understood the new method yet.
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UberLord · Posted: Wed Nov 10, 2004 5:07 pm Post subject:

tecknojunky · Posted: Thu Nov 11, 2004 7:26 pm Post subject:

I have many difficulties. I always wondered why Gentoo has to complicate things by abstracting the network configuration.

I simply want to route traffic between two vlans. Following your howto, compared to when I do a manual configuration, I end up with eth0 having an ipv6 address, unable to define a default gateway and with SIOCSIFMTU error, probably due to the mtu 1504 defined in your wiki. I also have to spoof the mac address.

So here is how I configured /etc/conf.d/net

flickerfly · l33t Joined: 08 Nov 2002 Posts: 677 Location: Lanham, MD

gtsquirrel · Posted: Thu Nov 11, 2004 11:32 pm Post subject: Adding VLAN options

Hey,

Thanks for posting this! I was about to add my own /etc/init.d/vlan script to handle this apart from the regular Gentoo network initialization. I did have a few questions, though.

vconfig has lots of different options, so I'm wondering how to customize that in the /etc/conf.d/net file. How can I specify a PER_DEVICE or a PER_KERNEL bind-type? And how can I specify a naming scheme to use? (VLAN_PLUS_VID, VLAN_PLUS_VID_NO_PAD, DEV_PLUS_VID, DEV_PLUS_VID_NO_PAD)

I took a brief look at the code in /etc/init.d/net.eth0, but didn't really see anything that looked to be for this.

Thanks!
chris

tecknojunky · Posted: Fri Nov 12, 2004 1:44 am Post subject:

Well, I finaly got fed up learning stuff way too off and complicated. I decided to simply put the ifconfig and route commands directly into the net.eth0 script. Suddenly, life became much simpler.
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UberLord · Posted: Fri Nov 12, 2004 10:54 am Post subject: Re: Adding VLAN options

gtsquirrel · Posted: Fri Nov 12, 2004 9:59 pm Post subject:

Actually, it appears as though PER_DEVICE and PER_KERNEL support has been stripped from vconfig 1.8. I wonder what else they've changed ...

Thanks!
chris

tecknojunky · Posted: Sat Nov 13, 2004 4:23 am Post subject:

Bummer, another tile fell on my head.

iptables do not support aliases or vlans. So, I've put in a second nic.

The downside is that it's connected to the same switch, so I'm using two ports. Kinda dumb when you know the switch and Linux can both talk vlan.

It would seem that iptables2 could do that, but it looked radically different in terms of commands, and I need a router now, not in two months.
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