Re: status of VLAN support in Debian/Linux in general
1.) VLAN is an IEEE Standard. (802.1q).
But there are two kind of VLAN: tagged VLAN and untagged ones.
a.) The untagged ones work only "within one switch", i.e. the switch
is able to 'partition' itself into several logical switches. This is not
what you want.
b.) The tagged one are 802.1q. This is what you are looking for. All
frames are tagged with a VLAN Header, which is 4 byte long. That makes
Ethernet-frames with vlan 1504 bytes long altogether (layer 2 -> no
While the kernel itself has no problems with 1504 byte frames, some of
the ethernet drivers had. This is what the patches on the candelatech
page are for (Thanks Ben Greer!). They fix several drivers in 2.4 series
(in my case I had to patch the tulip driver - many 4 port cards use
tulip. NB: The tulip patch does not apply tp 2.6 series)
Other cards don't need patches (I can confirm: yukon/marvell (sk98lin)
rtlXX and intel working). I don't know if they fixed up all drivers in
2.6 series (Anyone knows??)
2.) For those who were afraid about mixing VLAN-capabale swicthes of
- Basically VLAN is 100% compatible, we run D-Link, Allied Telesyn,
3COM, Cisco, and some no-namers togther with extensive VLAN usage.
- Vendors tend to use differnet approches and terminology for the config
interfaces (egress, forbidden, PVID, VID, group etc...)
- Many switches have a limited range of VLAN IDs. Normally it's up to
4096 possible IDs. Some D-Link only accept up to 512, 3 COM Superstack
even less, some have 1024 or 4072.
3.) If you want to 'cascade' switches or run tagged frames through
non-managebale swicthes you have to press thumbs that the cheap ones
support 1504 byte frames. Many do. Test your setup with with a crossover
4.) Hint: If you setup VLAN with /etc/network/interfaces please keep in
mind that the physical interface has to be up in order to create VLANs
on it, i.e. you have to set somme (dummy?) IP to ethX in order to create
5.) For those using a catalyst switch to terminate the vlan - there is a
confirmed bug in the cisco asic. Don't wonder why the error LEDs blink.
Mr. Sascha Pollok wrote a patch that add a padding to the frames so the
cisco gets more happy.
6.) To our experience the usage of VLAN does not cause siginifcant CPU
load on linux.
Tel: +49 69 85700331
Adrian 'Dagurashibanipal' von Bidder wrote:
I've some questions regarding VLAN support in Debian and in Linux. First: is
<http://www.candelatech.com/~greear/vlan.html> still the main page? Google
makes me think so, but there are some references to 2.2 kernels and none to
2.6 kernels, so I'm a bit unsure.
2.6 kernels: are they ready in general? The kernel.org and/or the debian
kernels? kernel-patch-vlan is only in woody, so I guess recent 2.4 kernels
don't need patches.
Which ethernet cards are working? I'm interested in both fast ethernet and
VLAN is an IEEE standard - is it a real standard, or is it a 'it may work
with some switches and not work with others'? (The simple format of the
VLAN tag in the ethernet header makes me hope for the former...)
Debian: Ok, I see there's the package 'vlan', so I guess it contains all I
(Yes, some of the questions could be solved by experimenting - however, I
don't have a VLAN capable switch yet. In fact, all I have is a 5 port 10M
hub, an a couple of Realtek 10M network cards. Go figure...)