What is vlan mapping and how can I apply it to my network?

[alanchia2000]

Hi,

Does anyone here know what is vlan mapping and how can I apply it to my network? I been trying to figure out what the Cisco press book for BCMSN is writing.

[paddyxdoyle]

Hi,

Is it talking about VMPS?

This is where you create a text file on a TFTP server containing host MAC addresses and map them to a specific VLAN.

You then set the switch ports to be dynamic and when you enable VMPS the switch downloads the table from the TFTP server and loads in into memory.

Once a client connects to the port its MAC address is sent to VMPS and the connection is either permitted or disabled.

This way you can control which VLAN a host is in if that host moves around your network.

I don't think VMPS is supported on all switches plus i heard Cisco were going to pull support for it.

HTH

Paddy

[alanchia2000]

Hi,

Thanks for being helpful but I was not referring VMPS.

What I meant what mapping from 802.1Q to ISL VLANs? Is there any purpose in it?

[Georg Pauwen]

Hello,

check this explanation from CCO:

´The valid range of user-configurable ISL VLANs is 1-1000. The valid range of VLANs specified in the IEEE 802.1Q standard is 0-4095. In a network environment with non-Cisco devices connected to Cisco switches through 802.1Q trunks, you must map 802.1Q VLAN numbers greater than 1000 to ISL VLAN numbers.

IEEE 802.1Q VLANs in the range 1-1000 are automatically mapped to the corresponding ISL VLAN. IEEE 802.1Q VLAN numbers greater than 1000 must be mapped to an ISL VLAN in order to be recognized and forwarded by Cisco switches.´

Have a look at this link:

Mapping 802.1Q VLANs to ISL VLANs

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_5_5/sw_cfg/vlans.htm#xtocid2080214

HTH,

GP

[alanchia2000]

Hi,

That is the part which I don't understand and was added to the Cisco press book without any explanation.

Why do you want to do vlan mapping when one is already sufficient? Is there any purpose in mapping 802.1q VLANs to ISL VLANs. The keyword here is rationale. What is the rationale of doing it?

[Georg Pauwen · Accepted solution]

Hello,

I think it works like this: you have an 802.1Q trunk with another external (e.g. non-Cisco) device. Let´s say the VLAN number is 1078. Within your network, you are running ISL only. Without the mapping, the 802.1Q VLAN would be dropped as soon as it gets on an ISL trunk, because ISL does not support VLAN number 1078. With the mapping, the 802.1Q VLAN is translated to a VLAN that ISL can handle, and hence forwarded over the trunk.

HTH,

GP