Secodary IP with different netmask

[Rick Morris]

Forgive my basic question!

I am migrating several networks into one.  As a part of doing this I want to have little to no disruption of service.  I am taking 5 SVI's and collapsing the networks into 1

VLAN 80 will be the one standing SVI with a /21

In each of the other SVI's, 81, 83, 85, and 87 each has a /23

Can I set up the secondary IP in the following"

Interface VLAN 80

ip address 192.168.80.1 255.255.248.0

ip address 192.168.81.1 255.255.254.0 secondary

ip address 192.168.83.1 255.255.254.0 secondary

ip address 192.168.85.1 255.255.254.0 secondary

ip address 192.168.87.1 255.255.254.0 secondary

The question is, does the netmask need to match the primary or can I use the netmasks as configured in the example above?  This will allow users who have the default-gateway configured statically to not have to change it night of cut.

Thanks,

Rick

[Richard Burts · Accepted solution]

Rick

There is no requirement for the netmask of a secondary address to match the netmask of the primary address. So from that perspective you have no problem with what you suggest.

HTH

Rick

[Rick Morris]

As always Rick, thanks for the assistance.  I could not find anything witha quick search and have never set it up that way before.  I figured it could be done but wanted someone much smarter than me to set me straight!

Thank you!

[Joseph W. Doherty]

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Posting

As Rick has also posted, secondary IP address masks don't have to match the primary IP address mask, but what you're doing, overlapping the interface address space, is just looking for issues.  I would suggest you migrate to a new non-overlapping address block.

I also wonder, you really want a single VLAN with a /21?