Вот нашел здесь:
http://www.cisco.com/en/US/products/hw/routers/ps274/products_qanda_item0900aecd802a9470.shtmlтипа, больше 15 vlan'ов на 2821 никак не получить?
VLANs
Q. What is the VLAN database?
A. The VLAN database is a file that resides on the compact flash memory of the Cisco integrated services routers. This file contains detailed information needed to identify individual VLANs to the system, so that traffic to and from those VLANs can be properly identified. A VLAN must be created in the VLAN database before it can be used, even though interfaces can be assigned to it. If interfaces are assigned to a VLAN not present in the VLAN database, traffic does not flow properly. In order to ensure correct working of VLANs, the compact flash memory must be installed securely. You cannot swap it with another compact flash memory and expect VLANs to work. The Cisco EtherSwitch Service Module contains its own VLAN database, stored in NVRAM on the module. It has no dependency on the compact flash memory, nor does it have access to the vlan.dat file.
Q. Can I remove the compact flash memory from the routers while they are running?
A. Do not remove the compact flash memory during network operation. Removing this memory from the router during network operation can result in unpredictable behavior in the platforms. The vlan.dat file, along with several other files, are written to and stored on the compact flash memory. If the flash memory is removed during operation and the router needs to access those files, it may react unpredictably, including not forwarding packets. At that point, a power reset may be required.
Q. Can I create VLANs in the VLAN database from config mode?
A. No, VLANs can be created only directly in the VLAN database. Configuration lines in the global config mode will not create entries in the file.
Q. How many VLANs are supported on the Cisco EtherSwitch modules?
A. Table 4 shows the number of VLANs supported per platform by the Cisco EtherSwitch modules. When a Cisco EtherSwitch HWIC is included in the stack, the maximum allowed number of VLANs is 15, regardless of platform capacity.