Secondary VLAN IP address in same subnet as the primary IP - NO GO!

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Anyone have a clever way around this issue?

I am 90% migrated from an old Cisco environment. I had an issue where one of my vendors was running around setting the wrong gateway IP address on radiology equipment. To fix the issue on the Cisco stuff (many moons ago) I added that address as a secondary IP to the VLAN IP address.

Now - many years later I am trying to reproduce this on my Extreme environment but EXOS won't have it. It's telling me that my secondary IP address is in the same network as the primary IP address (which is true). But I sort of need that to work.

If anyone knows a neat trick around this - please share!  :-)
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Steve Ballantyne

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Posted 11 months ago

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Eric Burke

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Not 100% sure, but you may need to add a new virtual router in order to accomplish this. My sense is that you'd then have to do the same for your upstream network(s) too so likely not ideal in your example...
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Brandon Clay, Escalation Support Engineer

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I've seen VRRP used for this scenario. Just create a VRRP instance on the VLAN with the VIP set as the same address as the secondary IP on the Cisco.

Being the only VRRP router in the VLAN, it should always be master.

The only downside is periodic VRRP adverts, but you could turn up the advertisement interval to reduce that if you wanted to.
(Edited)
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Steve Ballantyne

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Thanks! This is the kind of silly solution I was looking for. I will give this a shot.
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Drew C., Community Manager

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That's disgustingly clever... I like it! haha
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Steve Ballantyne

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Hello folks, because I love to reply to my own threads - and because I am just now getting around to moving this VLAN 10+ months later, I decided I would drop a few lines for future readers on how it went down.

Using Brandon's suggestion, I threw in a new VRRP and gave it an IP address. And that was all there really was to it. Easy!

Here is what the config looked like ...

create vlan "Radiology" tag 172
configure vlan Radiology add ports 48 tagged
configure vlan Radiology ipaddress 172.21.114.1 255.255.255.0
enable ipforwarding vlan Radiology
enable bootprelay vlan Radiology
create vrrp vlan 172 vrid 1
configure vrrp vlan 172 vrid 1 add 172.21.114.201
enable vrrp vlan 172 vrid 1
In this example - I gave a VLAN called "Radiology" and it has a VLAN tag of 172. The actual gateway IP (aka the VLAN IP) ends in .1, but .201 is what some devices were randomly configured to use.

Thanks again Brandon!
(Edited)