Secondary IP address on VLAN interface

[davidhvoss]

We are migrating our IP design from 192.168 to 10.2 networking. I would like to make the transition seamless while supporting both networks at the same time. Can I support 2 networks on the same vlan?

int vlan 101

ip address 192.168.1.1 255.255.255.0

ip address 10.2.1.1 255.255.255.0 secondary

It accepts this change, but I just want to make sure I'm not bumping into hidden issues. I plan to do the same thing to over 5 vlan interfaces.

int vlan 102

ip address 192.168.2.1 255.255.255.0

ip address 10.2.2.1 255.255.255.0 secondary

int vlan 103

ip address 192.168.3.1 255.255.255.0

ip address 10.2.3.1 255.255.255.0 secondary

int vlan 104

ip address 192.168.4.1 255.255.255.0

ip address 10.2.4.1 255.255.255.0 secondary

int vlan 105

ip address 192.168.5.1 255.255.255.0

ip address 10.2.5.1 255.255.255.0 secondary

[xephael]

Did you ever get a reply to this, or did it work for you?

[davidhvoss]

No reply yet, but I just posted it. The command works (the switch accepts it) but I'm concerned about hidden issues. Wondering if anyone else has tried this.

Although the subnets above our not our actual network design, I think people will get the idea of what I'm shooting for.

[jgross]

Hi,

do you use DHCP for the clients ? Do you have a helper-address configured on the vlans.

If so, you migth get trouble with DHCP because the router uses his primary address as source when he forwards a dhcp request. If you migrate it will work fine, but then clients cant renew their dhco lease. One day when the dhcp lease time is over your clients will have trouble to get a new ip address.

Bye

Jo

[davidhvoss]

Thanks. Yes we use DHCP and helper-address command, but only for users and printers.

I think what I can do is:

make 10.2 address primary address for non-DHCP subnets

When we are ready to migrate the DHCP subnets, we will make 10.2 address primary and activiate the new DHCP scope at the same time.