I have a VLAN that is 10.0.0.0/16 based. I want to create another VLAN that is 10.0.1.0/24 based for migration purposes. Given that these will be on the same box I would guess bad things would happen. Would the switch even allow me (I am guessing not) to create the new VLAN? If so, what would happen if I did?
Sorry, forgot that minor detail. It is a 4510R running 12.2(20)EWA
Yes, migrating is always fun... ;)
The switch will not allow this... last time I had to do this I used a router, mainly because we were using extreme switches and they didn't support this at the time.
The IP range was, 10.10.10.0/24 and the gateway was 10.10.10.1. We ran out of IP space so we had to change the masks, it went rather smoothly by adding 10.10.10.1/16 as a secondary IP address and the VLAN's did not have to change. Just had to run around and change all the subnet masks on all of the servers at our leisure. Took about two weeks to change all of the masks, but there was zero downtime.
Wil my 3¢
Hark> I have a VLAN that is 10.0.0.0/16 based. I want to create another VLAN that
In article , Harkin wrote: :I have a VLAN that is 10.0.0.0/16 based. I want to create another VLAN that :is 10.0.1.0/24 based for migration purposes. Given that these will be on the :same box I would guess bad things would happen. Would the switch even allow :me (I am guessing not) to create the new VLAN? If so, what would happen if I :did?
It's going to depend on the switch software; you didn't happen to mention the manufacturer, model, or software version.
Some devices would notice the overlap, but some will not (e.g., PIX documentation prohibits it but the 6.3(*) software does not notice in the case where one is a proper subset of the other.)
Layer 2 switches aren't going to notice because they don't ascribe any layer 3 meaning to the VLANs: the VLANs just -are- as far as they are concerned.
Layer 3+ switches that don't notice the overlap might use longest- match routing. Or, as they say in comp.lang.c, they might provoke nasal demons.
In message , Harkin scribes
The whole point of a VLAN is that it separates layer 2 networks, unless it is a routing switch it won't give a monkeys about the IP address range you use on that network.
If you have a router between the two VLANs then that is a different storey. Over to the router chappies.
As long as the layer 3 device allows VLSM (Variable Length Subnet Masking) then you are set, wheter that device is a router or L3 switch. Otherwise, it won't work.
I attempted to add a 10.1.14.0/24 VLAN to discover the result. When I attempted to assign the 10.1.14.1/24 IP address to the interface I was informed that the address overlaps with the 10.1.0.0/16 VLAN and would not be allowed.
I guess that I need to just move into a different class C range (10.2.x.0/24) and migrate to that one, then dump the 10.1 network?
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