Cisco – multiple subnets on the same cisco switch port

ciscosubnetswitchvlan

We have several servers on colocation and now trying to re-organize the network by utilizing Cisco ASA 5505 as a router and Cisco 3750x series switch.

Network topology is looking like that:

    uplink
      |
+----------+
| ASA 5505 |
+----------+
      |
      |(trunk vlan10,101,102)
      |
+-----------+
|   3750x   |
+-----------+
      |
      |
      |
+--------------------------+
| Server N                 |
| 192.168.10.10  : vlan10  |
| 192.168.101.10 : vlan101 |
| 192.168.102.10 : vlan102 |
+--------------------------+

The problem with 3750x configuration as we need to deliver three different subnets (vlan 10,101,102) to the "Server N".
"Server N" has multiple IPs from different subnets (vlan101 and 102) assigned to the same NIC. Plus, it has Base Motherboard Controller on board with another IP from vlan10. BMC shares the NIC – thus there is only one physical link from the server to switch.

Since 3750x doesn't allow having multiple vlans allowed on the same port with out trunking – what is the best way to configure the switch to allow this configuration?

UPDATE 2014-02-24:

The original question was asked a long time ago, so let me post the solution i found working for me with out messing with trunks and recompiling the system.

I used static routes to deliver traffic over a vlan to a server secondary addresses.

for the configuration above, the NIC has three subnets. Let's consider one of them as primary and include into VLAN configuration. Other two are going to be a routed subnets.

Here is the simple config:

    interface Vlan1
     ip address 192.168.10.1 255.255.255.0
    !
    ip route 192.168.101.0 255.255.255.0 192.168.10.10
    ip route 192.168.102.0 255.255.255.0 192.168.10.10

This way you can add multiple secondary subnets to your server.

However, i believe this is not the best way to configure it as it keeps secondary subnets out of VLANs – thus it's not as secure as we want it. But this is going my next questions to professionals.

Best Answer

Trunk the interface going to the server.

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