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Implement VLAN's over an existing large B Class

Occasional Visitor

Implement VLAN's over an existing large B Class

i have purchased a new HP 5308XL for my company.
Now the internal LAN are a large class B network, and all client and server are on the class :


Now i want to implement VLAN to reduce broadcast that is too high.
I think to modify the large class B into more small VLAN like this :


but my question is:

is possible to implement this VLANs that are part of the existing class B ?
Machine on the old class B can be co-exist with the new VLANs?
I can't migrate all the machine in one time, but periodically.
Thanks a lot for support.
Have the best time.
Matt Hobbs
Honored Contributor

Re: Implement VLAN's over an existing large B Class

Yes, you should be able to do this by enabling the proxy-arp feature on each VLAN.

ProCurve Switch 5300(vlan-1)# ip proxy-arp
Mohieddin Kharnoub
Honored Contributor

Re: Implement VLAN's over an existing large B Class


Additional to Matt's suggestion, Routing feature between the Vlans should be enabled on the 5300 Switch.

Good Luck !!!
Science for Everyone
Trusted Contributor

Re: Implement VLAN's over an existing large B Class

How many hosts do you have?

Since you only have one subnet, I assume you have noo router on your premisses, except for the internet router. In order to use more subnets in your LAN and have computers from various subnets communictae to each other, you will have to have an inter-VLAN router (which can be Layer 3 switch), that can perform routing at high speeds.

You could use another private class B network for subnetting: like; - these will give you 254 hosts per subnet (or; - which will give you 510 hosts per subnet) to make your change. Just define these scopes in your DHCP server, define the new VLANS and associate one IP subnet from the above to VLAN interfaces, and then progressively move hosts from your original subnet into these new subnets.

I would further suggest to plan your subnets for these needs:
1. management 254-host subnet for your switches (I would use VLAN1 of all switches for this)
2. printer 254-host subnet, in which to put all printers and print servers (to minimize routing traffic in the inter-VLAN router)
3. one or more 254-host subnets for company-wide servers, for all servers you may have (to be able to control access to your servers) - this may require to re-assign IPs for your servers, but you might want to keep for this purpose, since it will not have so many broadcasts once you managed to move all other devices in their respective subnets
4. one or more subnets for your PCs (you might want to use 510-host subnets for this, to minimize your work on future Access Control Lists and DHCP settings, since broadcasts in 510-client segments is totally acceptable
5. one 254-host subnet for direct internet access and no access to your internal LANs (for the guests your company may have that require only internet access)

Also you could use subnets to keep different departmets of the company, since Finance and Engineering departments of your company might have differing requirements. To minimize inter-VLAN traffic you could put departmental servers in the department's subnet. This might work well if you have managed switches in which you can define VLANs in all your wiring closets.
Trusted Contributor

Re: Implement VLAN's over an existing large B Class

And since you are from Europe, I could help you practically in implementing this.
Occasional Visitor

Re: Implement VLAN's over an existing large B Class

hi ,thanks.
with the ip proxy-arp command, now inside the small VLANS i can see the old big class B's ok!!!
but some servers in class B (like mail server) don't see machines on your class B network. His arp cache not have the right arp address of some machine...but take the arp address of my switch hp 5308xl and is no good.

When i disable ip proxy-arp on switch, on my VLANS i can't communicate.

any suggestions?