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Configuring  2 or more IP's on virtual interface

Posted on 2014-07-24
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Last Modified: 2014-09-25
Is it possible to have a virtual interface on a layer 3 switch have more than 1 IP assigned to it?

For example, I'm merging multiple VLAN's together to be 1 VLAN, but a couple of these VLAN's have some devices that are set statically. I'm changing the IP ranges these networks were on so that the new subnet includes all of the old addresses.

For example, one vlan was 192.168.10.1 / 24 and another one was 192.168.11.1 / 24

I'm changing my addressing so I will now have 192.168.8.1 / 22, but I have devices statically assigned in the 11.1 /24 subnet that have a gateway of 11.1. I'm keeping the 192.168.10.1 network / vlan, I'm just chaning it's mask to a /22 rather than /24. So my new range will be 192.168.8.1 - 192.168.11.1. I was going to leave the gateway as it was on that virtual interface so it will stay the same at 192.168.10.1, and I just have to update my DHCP scope with the new mask. However, I have quite a few static devices on 11.1 / 24 currently that point to 11.1 as their gateway. When I modify this virtual interface to go from 192.168.10.1 /24 to /22 is there a way I can have a second IP on that virtual interface as 11.1 so my devices in that IP range will continue to work until we are able to get to all of them to change the gateway?

Or is there a easier way to do this and I'm over thinking guess? I'm just trying to figure out what's the easiest way to allow my devices with static IP's to continue to work till we can change their gateway?
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Question by:themightydude
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Expert Comment

by:Sid6_7
ID: 40218498
I am wondering if this could work with subinterfaces on the switch. If the switch has that option. I think i tried doing this a long time ago, but dont recall if it was successful or not. Any other expert can shed some light?
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by:themightydude
ID: 40218504
If this helps any, our virtual interfaces are all setup on our core switch which is a Brocade FastIron SX800.
The IDF switches are the FastIron GS series switches.
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Accepted Solution

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Sandeep Gupta earned 500 total points
ID: 40218632
Yes you can put second IP address on virtual interface as 'secondary'

int vl 1
ip address <<primary ip>> <<mask>>
ip address <<secondary ip >> <<mask>> secondary

remember: DHCP will only switch on to secondary when primary hosts are exhausted..or else you completely remove primary.
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Author Comment

by:themightydude
ID: 40219564
Ok cool..so I should be able to to have my primary IP of 192.168.10.1 /22 as the IP for that virtual interface, then have 192.168.11.1 / 22 as a secondary IP on that same virtual interface.
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Expert Comment

by:Sandeep Gupta
ID: 40238490
your

192.168.10.1 /22  & 192.168.11.1 /22 falls int the same subnet of 192.168.8.0 /22 then what makes sense to have primary or secondary..if you have only primary 192.168.10.1 /22 it will automatically takes IPs till 192.168.11.0 /22
see this:

Calculation results

Address

192.168.8.1

11000000.10101000.00001000.00000001


Netmask

255.255.252.0 = 22

11111111.11111111.11111100.00000000


Wildcard

0.0.3.255

00000000.00000000.00000011.11111111

 

Network

192.168.8.0/22

11000000.10101000.00001000.00000000

Class C


Broadcast

192.168.11.255

11000000.10101000.00001011.11111111


First IP

192.168.8.1

11000000.10101000.00001000.00000001


Last IP

192.168.11.254

11000000.10101000.00001011.11111110


Hosts/Net

1022

nnnnnnnn.nnnnnnnn.nnnnnnhh.hhhhhhhh
Private
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Author Comment

by:themightydude
ID: 40344918
Sorry for staying away from this for so long.

I was able to do the primary and secondary on the core swithces and it worked perfectly.
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