Flat & Switched Network to Routed Network with Vlan's

[raju]

Hello ,

It's simple question. We have a process Network which is a flat, Switched Network with FDDI backbone and it is an isolated Network using public IP scheme

155.222.0.0/255.255.0.0 . We are planning to change to Gigabit Backbone based on 6509 with MSFC2 and introduce Layer-3 Vlan's to limit broadcasts . The current IP address scheme can't be changed as it requires reconfiguration of cluster servers which are very critical. The servers have the IP addresses like 155.222.5.10 /255.255.0.0 , 155.222.6.10 /255.255.0.0 , 155.222.7.10/255.255.0.0 without Gateway since it's a purely Switched NW . I'm trying to simulate 6509 setup in offline with 3750 Switch by creating Vlan's and assigning IP addresses . For example Vlan 2 will have an interface IP address as 155.222.5.1/16 , Vlan 3 will have 155.222.6.1/16 , vlan 4 will have 155.222.7.1/16 etc and but it gives overlapping . Instead , I can go for 155.222.5.1/24 , 155.222.6.1/24 , 155.222.7.1/24 and in that case it's requires change of mask which I need to change on all server side while configuring Gateway address in servers .

Any other idea pls ...

Regards,

Raju

[Georg Pauwen]

Hello Raju,

you can use a mask of 18 (255.255.192.0) or higher to get 4 subnets. I am afraid that in your production environment, you have no choice but to change the mask and default gateway reflecting any change in your addressing scheme.

Regards,

GP

[raju]

Thanks gpauwen .

Well, I need more subnets becoz apart from servers , PLC devices and Automation system workstations are in different subnets . In current environment ,these devices are located in different subnets (not really subnets because of it's switched ) from 155.222.1.0/16 , 155.222.2.0/16 like until 155.222.20.0/16 means I have to keep all subnets in new Vlan environment in 6509 to reflect (maintain) same IP addresses . Apart , I need one subnet exclusively for Management Vlan and keep some subnets (say 10) reserved for future use. While considering all these , what is the best subnet mask ?

Thanks again..

Raju

[Georg Pauwen]

Hello Raju,

every bit added to the mask doubles the amount of subnets:

155.222.0.0/17 --> 2 subnets

155.222.0.0/18 --> 4 subnets

155.222.0.0/19 --> 8 subnets

155.222.0.0/20 --> 16 subnets

and so on. Just be aware that (obviously) for each subnet you cannot use the first address (network) and the last address (broadcast) for host addressing.

Does that answer your question ?

Regards,

GP

[raju]

Thanks GP. Obiviously, I can't use first and last addresses for host's as it's reserved for Network and broadcast.That's ok.

I'll go for 155.222.0.0/24 sothat I can have 256 subnets and each subnet will have 254 (256-2) addresses for host's assignment.Am I right ?

Regards,

Raju

[Georg Pauwen]

Hello Raju,

you are exactly right, 155.222.0.0/24 will give you 256 subnets with 254 hosts each.

Regards,

GP

[raju]

Hello GP ,

Thanks a lot and appreciated. So, there is no way to carry over the same mask which is in Switched Network to Routed Network (Vlan's ) like 155.222.1.0/16 , 155.222.2.0/16 -- 155.222.256.0/16

Regards,

Raju

Regards,

Raju

[Georg Pauwen]

Hello,

if you want all devices to talk to each other and just subnet them, you have no other choice but changing the mask. There is a feature called Private VLANs, wich allows you to isolate ports within a VLAN and to ensure that only those ports can talk to each other, but I guess that won't help you much...

Regards,

GP