Creating two SVI Interface on MSFC with same IP range Concept

[ambivert skill]

Hello Experts ,

I have one question regarding the InterVLAN routing concept of L3 devices for a specific scenario.

Suppose we create 4 SVI Interfaces with the following details on MSFC.

1.VLAN 10 with IP Address : 192.168.10.10

2.VLAN 20 with IP Address : 192.168.20.20

3.VLAN 30 with IP Address : 192.168.30.30

4.VLAN 40 with IP Address : 192.168.10.20

So by the InterVLAN routing traffic move from one VLAN to another.

Now suppose if I configure 2 Pc's(A&B) for VLAN 10 with default gateway : 192.168.10.10

and configure another 2 Pc's(X&Y) for VLAN 40 with default gateway : 192.168.10.20.

Will PC A will communicate with PC X through intervlan routing however they are in same IP subnet.

Regards

Ambivert SKill

[InayathUlla Sharieff]

Hi Ambivert,

You will get the following error when you try to configure the same subnet address on the vlan interface.

Vlan10                 192.168.10.10   YES manual up                    up

Vlan20                 192.168.20.20   YES manual up                    up

Vlan30                 192.168.30.30   YES manual up                    up

Vlan40                 unassigned      YES unset  up                    up

SwitchA(config-if)#ip address 192.168.10.20 255.255.255.0

% 192.168.10.0 overlaps with Vlan10

2-

I may be wrong if you have already configured it. If yes then kindly share the config so that we see they way you have configured.

HTH

Regards

Inayath

[aras.sepehri]

You cannot assign two IP addresses within a same subnet to two interfaces.  

[Bilal Nawaz]

Hello, Cisco IOS does not allow you to configure ip addresses within the same subnet on two different interfaces by default.

However, this is achievable with the use of VRF's - (rarely used, perhaps for advanced routing)

your PCs that are in vlan 10 and 40, on the same subnet will need to be within the same vlan in a normal case to be able to communicate properly.

To get to anything else, it will be routed via the default gateway.

You could make the subnet smaller so instead of using a mask of 255.255.255.0 a /24 you could use 255.255.255.240 /28 which will give you address space from 192.168.10.0 - .15 which allows for 14 hosts within this network.
And likewise same for this 192.168.10.16 - .21
Example:
Interface vlan 10
IP address 192.168.10.1 255.255.255.240

Interface vlan 40
IP address 192.168.10.17 255.255.255.240

Hope this helps

Sent from Cisco Technical Support iPhone App

[ambivert skill]

Bilal actually I need to clear this for the deployment of FWSM in transparent mode,Please check thees two PDFs.

The information mention in them are as follow.

PDF1:  I have create one design in which I put inside interface of FWSM into  public VLAN 170 and I think that internal traffic should move like this.

7613(G9/5)  --> 6513(G10/4) --> ISA (Internal Int.) [NATing] (ISA External  Int.) -->6513(G9/45){This is L2 port in VLAN 170} --> VLAN 170(SVI  Int,IP:192.168.40.20) --> Inside Interface of FWSM and we will do  bridging on FWSM to connect Inside and outside Interface of FWSM.

Problem : I am not very much clear regarding traffic movement from External Interface(FWSM) to Gi9/44 will it move ?

FYI : I am planning to move Gi9/44 to VLAN 120 currently it is in VLAN 170 as no FWSM is configured right now.

PDF2:  I think that if we will create another SVI Interface ie VLAN 120 with  IP 192.168.40.60 will this config work for passing traffic through FWSM.

I  am concern that will it by pass the FWSM if we will create another SVI  of same subnet i.e192.168.40.60 and please let me know will the concept  of VRF fit in this scenario.

Regards

Ambivert Skill