RHEL AS 4 U 4 and VLAN tagging (802.11q)

[Aly Dharshi]

Hello Folks,

	Okay to report back for completeness sake and so that if someone else 
is looking for this information in the mailing list they can get it.
	Firstly thanks to Ronan and Kevin for their postings and thoughts. We 
have a Cisco 4948 (access) switch. I think that 802.11q has been around 
on Cisco switches and routers long enough that I am pretty sure that 
anyone who works with them can set this up easily. My network people 
were able to do this easily enough.
	
	I followed the path of not giving the regular eth2 interface any IP or 
netmask, proceeded to create the vlan'ed sub-interfaces of eth2 as follows:

	vconfig add eth2 100
	vconfig add eth2 200

	These should yield via an ifconfig -a the sub-interfaces eth2.100 and 
eth2.200 as well as the parent interface eth2. So I setup in 
/etc/sysconfig/network-scripts/ifcfg-eth2 as follows:

DEVICE=eth2
BOOTPROTO=static
HWADDR=<MAC of this interface>
ONBOOT=yes
TYPE=ethernet

	You need this interface to be up in order for the sub-interfaces to work.

ifcfg-eth2.100 looks like:

DEVICE=eth2.100
BOOTPROTO=static
HWADDR=<MAC of eth2>
IPADDR=1.2.3.4
NETMASK=255.255.255.192
ONBOOT=yes
TYPE=ethernet
VLAN=yes                       <------ this is the important one

Replicate and change values to match for ifcfg.eth2.200 and you are set.

This should work, tweak your routes if required, and you are on for the 
races. Thanks for the info guys.

Cheers,

ASD.


	

Ronan Mullally wrote:
> On Thu, 24 Jul 2008, Aly Dharshi wrote:
> 
>> 	vconfig add eth2 100
>> 	vconfig add eth2 200
>>
>> 	ifconfig shows that I have 2 sub-interfaces eth2.100 and eth2.200 in
>> addition to eth2. The interface eth2 is already on vlan 200 with an IP
>> that is used on vlan 200. Can I use on eth2.200 in parallel with eth2 ?
>> Or will there be a conflict ? So can eth2 and eth2.200 use 192.168.100.2
>> for instance.
> 
> eth2 will work in "normal" mode, eth2.100 and eth2.200 will work in vlan
> mode - with a vlan header attached to the ethernet frame.  This is akin to
> "native" and "trunk" mode on a cisco switch or "tagged/untagged" on a
> Foundry or (IIRC) Extreme.
> 
> You won't be able to give two different interfaces the same IP address.
> I'm not sure off the top of my head what happens if you put both eth2 and
> eth2.200 in the same vlan and subnet.  The kernel will probably select one
> interface for sending traffic and the switch on the other end do likewise.
> They might not choose the same, so you might have traffic in one direction
> taking using eth2 and the other using eth2.200.
> 
> The safest bet is to just run everything on vlans and not assign an IP
> address to eth2.  Likewise, when you're configuring your switch port run
> it as a trunk (cisco speak) or a tagged port (foundry/extreme) and don't
> configure a native / untagged vlan on the port.
> 
> 
> -Ronan

-- 
Aly S.P Dharshi
aly.dharshi at telus.net
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