Change of IP range in same VLAN - Cisco Catalyst 3750 Stack

I need to change the IP range that I'm currently using in my LAN.
The issue here is that I need both IP ranges to coexist at least for a week until all the old IP addresses are cleared.

What are the steps to add the second IP range to my VLAN?

I'm thinking on adding a secondary IP address to the VLAN, and then add some routing between them.

Am I in the right track?
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Don JohnstonInstructorCommented:

ip address x.x.x.x y.y.y.y secondary

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cargexAuthor Commented:
So, right now I have this

interface Vlan1
 ip address

after I add the secondary IP address I will have this

interface Vlan1
 ip address
 ip address secondary

And will both networks coexist in the same VLAN?
Just like that?
Don JohnstonInstructorCommented:
Yes.  Sometimes things are easy... sometimes.
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Presumably, you will change the allocation scope on the vlan on the DHCP side.  If you are using a DHCP server, you would also need to change/update the ip helper configuration to reference the new ip segment to match the scope on the DHCP server to the new segment.
cargexAuthor Commented:
Good morning Don,
I just added the secondary IP, but from a test PC configured with an IP of the new range ( I can't connect to a device in the other range (

I can connect to other vlans, though.

What am I missing here?
Don JohnstonInstructorCommented:
You're not missing anything. It should work the same for the local addresses as the non-local addresses.

From a device on the network, can you successfully ping the address?

From a device on the network, can you successfully ping the address.
cargexAuthor Commented:
No, I can't.


Pinging with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Qualcomm Atheros AR8162/8166/8168 PCI-E F
ast Ethernet Controller (NDIS 6.30)
   Physical Address. . . . . . . . . : 08-9E-01-D1-E2-51
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   Link-local IPv6 Address . . . . . : fe80::818e:9b9f:6ce:286d%4(Preferred)
   IPv4 Address. . . . . . . . . . . :
   Subnet Mask . . . . . . . . . . . :
   Lease Obtained. . . . . . . . . . : Monday, July 27, 2015 9:07:11 AM
   Lease Expires . . . . . . . . . . : Tuesday, July 28, 2015 9:07:11 AM
   Default Gateway . . . . . . . . . :
   DHCP Server . . . . . . . . . . . :
   DHCPv6 IAID . . . . . . . . . . . : 252222977
   DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-19-83-F7-8C-08-9E-01-D1-E2-51

   DNS Servers . . . . . . . . . . . :
cargexAuthor Commented:
But from the device in the
I can ping the Cisco Stack
and I can ping ips in other vlans
Don JohnstonInstructorCommented:
There's your problem:

Default Gateway . . . . . . . . . :

According to your previous post, the (primary) IP address of the VLAN 1 interface is  

Change the default gateway to and you should be okay.
The addition of secondary IP range to a VLAN only competes that task, your issue is likely related to ACLs that restrict what traffic and to where is permitted to and from each VLAN and to the Internet.

What is on ip

Double check your 172.27.187 scope definition on the DHCP server and look at the options you are setting this is where the default IP and name servers you are pushing.
cargexAuthor Commented:
You are right, I can ping from a PC in to another PC in
But I still can't ping from the same PC ( to

I have a firewall on
That's our Internet access.
cargexAuthor Commented:
I think I have to add a new route to my firewall so that it knows where the is.
But it is requesting me to restart and I will need a window for that.

I will leave this question open until I can restart the firewall.

In your comment, your secondary VLAN IP is
I think to you are confusing the question. You need to post what IP and the information the segment ip is allocated and its settings.
Not sure where the segment is coming from.
Don JohnstonInstructorCommented:
If the default gateway is NOT the SVI, then the firewall will need a route to the secondary network.  And you may need to modify ACL's or any other permissions.
cargexAuthor Commented:
I added the route to the in the firewall ( and it started working.

Right now I have both networks
working together on the same Vlan1 and I can assign IPs of any of these ranges to any device and it can connect without any issues.
Exactly what I wanted.

Thank you very much guys, your help is greatly appreciated!
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