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Reducing a /16 network to a /24

I have a live network that is in the range.  I am creating VLANS and subnets and moving most of the nodes out of the range all together.  I was wondering though, is there a way to create a vlan/subnet in the range and keep communications up until I can change the grandfathered network to the /24 range?  Right now I'm going to have to take the network down, change the masks change the grandfathered range to a 24 and then create the VLAN that I need.

Anyway to do this with a live network?  Working with a Cisco 6509...
1 Solution
I don't see how this would work. Longer prefix will be put in the routing table thus cutting off traffic flow to /16.
publicvoidAuthor Commented:
Thought so but I though maybe there was some ninja solution I didn't know about.
bbaoIT ConsultantCommented:
> a way to create a vlan/subnet in the range and keep communications up

there is NO problem for hosts with /16 mask to communicate with others with /24 mask, IF:

1. they are in the same phsicsl network, VLAN or broadcast domain


2. the /16 mask hosts are actually in the range of

e.g. can talk with., but cannot talk to (technically the latter can receive the former's packets but will reply to other subsets if a default gateway is available).

does it make sense?

therefore if you carefully plan the IPs, new hosts can communicate with SOME hosts on the grandfathered network, though not all of them.

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