Exposing multiple VLANs to host

The wise Adam Przestroga enlightened me with:

- Make sure your host understands VLANS.

- Make sure you are using dot1q encapsulation on your trunk

- Make sure you are not not pruning vlans (when using VTP that is)

- Check the spanning tree state for the port

Greetz

Mark

Mark, wow I did not expect response within such short time! The trunk port is configured to use the dot1q encapsulation. Not sure regarding the remaining items though. How can I check and make my host VLAN aware? How to check the spanning tree state of the port? Finally, what is VLAN pruning and how to check this?

Regards, AP

if you don't know how to do that, I suppose that is the problem :-) The operating system on that host has to know how to deal with the dot1q encapsulation/understand VLAN's. This differs per operating system. Don't even ask me how to do it on Windows, I remember reading that only a part of the drivers understand it and I've never really investigated it, since I'd use Linux or FreeBSD for any decent work on networks (even troubleshooting).

So... check the manual or newsgroups on that OS.

Mark

I think that I did not make myself clear in the first post. I do not want the attached host to be aware of many VLANs on that port at the same time. All I want is to be able to attach say one host with IP address space of VLAN X and after disconnecting it another host with IP address of VLAN Y. I do not know whether there is anything special that I need to configure on the switch side to make it possible. I have configured the switch port as trunk with dot1q, but after connecting a host and configuring it for say VLAN X I was not able to ping the gateway IP address.

I don't think you understand what trunks and vlans do :-) I'd say: investigate a little bit. Trunking will tag the packets with a vlan tag. It's not a matter of 'accepting multiple ip ranges on one port'. The hosts will send untagged packets, and the only VLAN that it will work for is the VLAN you configured as 'native', default vlan 1. Actually: every packet sent by any of your hosts will arrive in the native vlan since it will be untagged. The return traffic will be tagged, so your host will not listen to them since it is not configured for tagged packets.

Mark

Adam, please chek this url:

url:

I don't think that you can do what you describe - other than by physically connecting the vlans with wires of course.

You plan violates the whole concept of VLANS and that is why there is no provision for it.

If you explain the problem that you are trying to solve then maybe someone can come up with another method to achieve it. The normal way to comunicate between VLANS is to use a router (or L3 switch - amount to the same thing).

Investigate - Dynamic VLANs, VMPS.

AFAIR you can rely on MAC Authentication Bypass (MAB) on a 3750 switch making RADIUS requests to a Cisco ACS server (this server will allocate a VLAN id to the port according to the MAC-address of the connected device). This is a workaround when deploying NAC on a network where some devices like printers that can't use 802.1X to authenticate.

Anyway, deploying MAB is probably a bad answer for this particular need. As per Mark's message, you should consider 802.1Q trunk ports on the switch, and 802.1Q on the server's NICs.

Maybe EEM (Embedded Event Manager) scripts can be another alternative to perform dynamic VLAN allocation on a Cat3750 or Cat4500 switch.

Regards,

- Ludal -

John Agosta wrote: