Multiple subnetworks in VLAN

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Jun 18th, 2009
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can someone help me with this problem?:

I have c6500 with 2 vlans.

First: vlan10 is using ip subnet are using default gateway

Second Vlan20 use subnet space gateway is

In vlan10 will be SAN network with IP space and in vlan20 SAN with subnet I need these subnets 172.16.x.x will be visible and SANs can be replicated. How to configure c6500 to allow comunication???.


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lubosbella Thu, 06/18/2009 - 06:04
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maybe better will be to see problem on picture (in attachment).

Sites are interconected by one wire in vlan20. So i cant create new VLAN there.

So how to setup switches that SANs can comunicate?.

lubosbella Thu, 06/18/2009 - 07:19
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this procedure is best, but im not sure if a switch in building B is managable and support to create VLANs.

If not, is possible to create in interface vlan20 second ip space/secondary ip address (ip address secondary) and in interface vlan10 secondary ip address ?

Then these subnets will be directly connected to c6500 and will be visible...

It is a good alternative idea?

lubosbella Thu, 06/18/2009 - 07:29
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Here is it:

IOS (tm) s72033_rp Software (s72033_rp-PK9SV-M), Version 12.2(18)SXD7b, RELEASE SOFTWARE (fc1)

ROM: System Bootstrap, Version 12.2(17r)S4, RELEASE SOFTWARE (fc1)

BOOTLDR: s72033_rp Software (s72033_rp-PK9SV-M), Version 12.2(18)SXD7b, RELEASE SOFTWARE (fc1)

Supervisor Engine 720 (Active) WS-SUP720-3B

lubosbella Thu, 06/18/2009 - 07:52
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and can you help me how to configure this routing? ....

- So we have:

interface Vlan10

ip address

interface Vlan20

ip address

- then i can add new VLANs:

interface Vlan30

ip address

interface Vlan40

ip address

But how to route them and assign them to interface?

When you create the VLAN - you also need to create the VLAN SVI.

Building B would be

interface vlan 40

ip address

ip route 192.168.100.x

Building A

interface vlan 30

ip address

ip route 192.168.101.y

x=4th octect of vlan interface in Building A

y=4th octect of vlan interface in Building B

lubosbella Thu, 06/18/2009 - 10:28
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Thank you very much Andrew.

Maybe some questions:

- i dont need to put this vlan 30 and 40 on same physicall interface? ... so physical interface where is connected building B to c6500 will be unchanged?

interface GigabitEthernet1/4

no ip address


switchport access vlan 20

switchport mode access

no cdp enable

spanning-tree portfast

- there are no others configuration changes for this routing except "ip routing"?

Only the interfaces on the respective sites that connect to the SAN need to be in the VLANs.

The VLAN/physical connection that connects the 2 buildings together does not need to be touched.

I would imagine that you already have "ip routing" enabled. so other than the static routes I posted earlier, no more routing config needs to be applied.


lubosbella Thu, 06/18/2009 - 11:19
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so one SAN interface which is connected to LAN is in building A. Here is SAN connected with one port to c6500. So config of this physical interface on c6500 will be:

interface GigabitEthernet1/5

no ip address


switchport access vlan 30 ???

switchport mode access

But if switch in building B is unmanagable then i cant configure this switch and i must to plug cable to this switch only....? but what than with vlan40?

Many thanks.

lubosbella Thu, 06/18/2009 - 11:40
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Ok if switch will be unmanagable then is better to buy new managable switch in building B...:)

Last question:

if i do a trunk link between buildings, is better to put SAN in building A in vlan 30 and put SAN in building in VLAN 40 or is better to use one VLAN (f.e.: 50) and put both SANs to this VLAN (in building A and B)?



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