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New Member

VLAN Overlapping - Don't Get it

Ok, I have a 1700 Switch with the FastEthernet 0/0 set as 10.10.10.1

If I create various VLANs, they give me the "hey buddy, it overlaps with Fastethernet 0/0" error if they are in the same

10.10.10.X range.

Naturally, I could define each of the VLANs and FastEthernet ports as 10.10.11.X and 10.10.12.X nets, but isn't there some way to have one or two of the FastEthernet ports in my basic 10.10.10.X networking scheme on this thing?

Clearly, I need some very basic knowledge here, but I don't understand why the additional VLANS couldn't be defined as unique 10.10.10.X addresses.

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Re: VLAN Overlapping - Don't Get it

that is correct ...

such as

10.10.10.0 255.255.255.192

host 1 -62, 63 broadcast

10.10.10.64

host 65 - 126 , 127 broadcast

10.10.10.128

host 129 -190 , broadcast 191

11 REPLIES

Re: VLAN Overlapping - Don't Get it

Rage,

Note that a router does not allow ip addresses to over lap on more than one interface. Your fastE interface and software interfaces such as Vlan 1,2,3 etc all are individual interfaces to the router's software. So it wont allow any set of overlapping between the subnets.

If 10.10.10.X has been assigned to fastE interface, you cannot assign an address to any other interface of the same router.

PS: There is no 1700 switch. Are you having a switch wic card on the 1700.

New Member

Re: VLAN Overlapping - Don't Get it

Yes, sorry... I was speaking generally.

This is a 1751V router with a WIC4ESW card

in it.

Purple

Re: VLAN Overlapping - Don't Get it

You can have other 10.10.10.X addresses in diferent vlans as long as the space is broken up with the correct netmask . You don't mention what mask you are using . It depends on how many host addresses you need in each subnet as which mask you'll use.

New Member

Re: VLAN Overlapping - Don't Get it

Ahhhh, I think that flicking little bulb

above my head is dimly lighting.

So, if I understand correctly, I can spread

the 10.10.10.X pie around the various VLANS

and the only real differentiation I need to

make, is that the subnet mask itself has to

preclude any overlap in the VLANS with regard to the actual IPs being utilized on those?

Purple

Re: VLAN Overlapping - Don't Get it

that is correct ...

such as

10.10.10.0 255.255.255.192

host 1 -62, 63 broadcast

10.10.10.64

host 65 - 126 , 127 broadcast

10.10.10.128

host 129 -190 , broadcast 191

New Member

Re: VLAN Overlapping - Don't Get it

Oddly enough now though, I see the Fastethernet 0/0 port is not tied to ANY vlan, nor does it offer me the "switchport" command in the configuration.

So I don't know how I would tie it to any

VLAN.

Our earlier discussed method would allow me to tie the fastethernet 0/1- 0/4 interfaces to

a defined VLAN, but can the built in 0/0 port be tied to one, and if so...how?

Re: VLAN Overlapping - Don't Get it

fa0/0 is a layer 3 port (router's built in port) and it cannot be tied to any vlan. Only fa0/1 through fa0/4 can be assigned to a vlan or make them a layer 3 port by using the command "no switchport".

int fa0/0

ip add 10.10.10.1 255.255.255.0

int fa0/1

ip add 10.10.20.1 255.255.255.0

no switchport

int fa0/2

switchport access vlan 3

int fa0/3

switchport access vlan 3

int fa0/4

switchport access vlan 3

int vlan 3

ip add 10.10.30.1 255.255.255.0

Now you have three subnets 10.10.10.0, 10.10.20.0 and 10.10.30.0.

The first subnet is tied to fa0/0 (router';s built in port)

The second subnet is tied to fa0/1 (the port fa0/1 has been made a layer 3 port using "no switchport" command)

The third subnet is tied to fa0/2,3 and 4 using a Layer 3 SVI interface (Vlan 3).

You should be able to route between these interface as long as PCs or other devices in each subnet are set with the right default gateway.

HTH

New Member

Re: VLAN Overlapping - Don't Get it

Sounds like this would be a resolution to

my problem alright...

However, when I attempt to do your suggestion

of int fa0/1

ip add 10.10.20.1 255.255.255.0

it responds

%IP addresses may not be configured on L2 links.

But I have indeed entered the

"no switchport" command on the fa0/1 entry....

so what's the deal with that? :-)

Thanks again for any advice.

New Member

Re: VLAN Overlapping - Don't Get it

Any further input on this

thisisshanky?

Still don't seem to be able to configure in

your suggested way after monkeying with it

all weekend.

New Member

Re: VLAN Overlapping - Don't Get it

Oddly enough now though, I see the Fastethernet 0/0 port is not tied to ANY vlan, nor does it offer me the "switchport" command in the configuration.

So I don't know how I would tie it to any

VLAN.

Our earlier discussed method would allow me to tie the fastethernet 0/1- 0/4 interfaces to

a defined VLAN, but can the built in 0/0 port be tied to one, and if so...how?

Purple

Re: VLAN Overlapping - Don't Get it

Don't think you have that option , it looks like that is a routed port only and you cannot tie it to SVI which you use to configure vlans on your 4 port switch module.

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