On Fri, Feb 5, 2010 at 05:12, Brad Edgeworth <[email protected]> wrote: > Can someone explain to me internal VLANS. I thought they were like > extended VLANs but it doesn’t seem to match up. I’ve looked over this > document but cannot find anything definitive.. > > http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.1E/native/configuration/guide/vlans.html#wp1032562 > > Is this something tied to the 6500 architecture for supporting various mods > (CSM, ACE, PIX, etc.)?
Some platforms (notably 6500/7600) use VLANs for "just about everything". For example, when you declare physical port to be a layer 3 port, the switch will create internal VLAN to represent this port. Think of it as a hidden SVI. Furthermore, when you create new VRF, internal VLAN will be created to represent that VRF. There are few other examples, but these two are the most common. On lower platforms, like 3560, internal VLANs are not consumed by VRFs, but they are consumed by L3 interfaces. You can see internal VLAN allocation by typing "show vlan internal usage". The display will contain the list of VLAN IDs used internally and what they are used for. There is limited control over which VLANs are used for these purposes. You can configure the 6500/7600 switch to start descending or ascending through the extended range, but on 3560 you are stuck with ascending. P.S. This can be real pain in production networks when you have box with a lot of VLANs and you are desperately trying to find available one on 5 of those ;-). You see, if VLAN is allocated for internal use, there is no easy way to de-allocate it, other than to reboot and let the box rearrange things... -- Marko Milivojevic - CCIE #18427 Senior Technical Instructor - IPexpert Mailto: [email protected] Telephone: +1.810.326.1444 Fax: +1.810.454.0130 Community: http://www.ipexpert.com/communities _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
