[c-nsp] multiple vlans on a port

[Cord MacLeod]

Thank you everyone for your replies.  Fantastic information.


On Jul 13, 2009, at 3:38 PM, Matthew Huff wrote:

> Yes, the machine will need to speak 802.1q. Most modern OS have no  
> trouble with that. Windows, Linux, Solaris, etc.. work fine with  
> 802.1Q.
>
> One thing more, unless Linux has started speaking Cisco DTP (which I  
> doubt), you want to disable DTP messages from sending to the host.  
> Dynamic Trunking Protocol (or DTP) is used to negotiate trunking  
> protocols (ISL or 802.1q), etc... Since you know you want to do  
> 802.1Q and you want to always trunk, you will want to add  
> "switchport nonegotiate" to the interface. This keep cisco from  
> sending a DTP frame every 30 seconds. Those frames won't hurt  
> anything, but can show up on port statistics as bad packets on the  
> host.
>
> Also, with 802.1q framing, you might run into fragmentation on the  
> non-native VLANs. You may want to adjust the MTU on the virtual  
> machines if Linux doesn't do it automatically.
>
>
> interface GigabitEthernet0/15
>   switchport access vlan 120
>   switchport trunk native vlan 120
>   switchport trunk allowed vlan 100,120,231,321
>   switchport mode trunk
>   switchport nonegotiate
> end
>
>
> ----
> Matthew Huff       | One Manhattanville Rd
> OTA Management LLC | Purchase, NY 10577
> http://www.ox.com  | Phone: 914-460-4039
> aim: matthewbhuff  | Fax:   914-460-4139
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net 
> ] On Behalf Of A.L.M.Buxey at lboro.ac.uk
> Sent: Monday, July 13, 2009 6:15 PM
> To: Cord MacLeod
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] multiple vlans on a port
>
> Hi,
>
>> I realize this is impossible, at least I have read it is on an access
>> port.  So if I sent up a trunk port with the machine, does the  
>> machine
>> need to speak 802.1q as well?
>>
>> interface GigabitEthernet0/15
>> switchport access vlan 120
>> switchport trunk native vlan 120
>> switchport trunk allowed vlan 100,120,231,321
>> switchport mode trunk
>> end
>>
>> The purpose of this is that the machine in a Linux machine running  
>> Xen,
>> so the cloud will decide what machines and vlans it needs to spin  
>> up at
>> what time.  Meaning this port will need access to these vlans.  This
>> being the case, will I need to configure the Linux machine for 802.1q
>> trunking as well?  I found this article that seemed to suggest,  
>> yes, but
>> I wanted a second opinion.  http://www.linuxjournal.com/article/7268
>
> Linux very happily talks 802.1q.  yes, if you want to feed multiple
> networks to the Xen host you need to send it a trunk feed... or invest
> in multiple NICs and assign NICs to virtual hosts. our Xen boxes
> get trunk feeds and /sbin/ifconfig lists all the pvlanXXX and  
> xenbrXXXX
> and xenbrtrunk etc.  VMWare has the virtual switch technology so  
> currently
> is _slightly_ ahead of Xen on that point...
>
> alan
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