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how to connect two networks together

Medium Priority
Last Modified: 2012-05-06
i want to connect the two networks belong
clients in 172.x.x.x needs to be connected to 192 network

it is possible to create a vlan in the 3750 switch, and clients 172.x.x.x can point there gateway to vlan

i want to implement connectivity without changing the gateway,
is it possible to use a firewall with 2 network cards? or a router? i havent seen a router with 2 ethernet interface
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Absolutly. The way you layed it out in your diagram would be one way to accomplish this.

Configure two VLANs on the 3750 and then connect each network to the VLANs. You can then allow or deny traffic between the two if you want. Then they will  both share the same Internet connection.

Create VLAN 192 and 172. Assign ports to each VLAN then connect each network to the respected VLAN ports. Then set the VLAN IP on the 3750 as the default gateway for all devices of that network.

Make sense?


attached new diagram

i cant do any changes in TEST1 network, ie: clients gateway

all what i got is a ethernet cable from TEST1 network

im thinking by connecting the cable to TEST2 layer 3 switch is it possible to route? or using a firewall with 2 NIC?

Yes, it is surely possible to connect both IP subnets with router, for example with simple windows machine with two network cards (need not be Win Server, sufficient is WXP, but need simple registry adjustment to do routing).
Then must be set proper configuration for clients to reach target through your added router.
It can be handled in general by two ways:
1. Router settings on the and which can to redirect client's request back to your router. But only of you can configure routers and
2.  Set routing tables in clients, for example with logon script, or I think also there is possible to add multiple default gateways on clients.

what  model is the test1 switch?

If the test 1 switch is a managed layer 2 switch it will be able to handle the separation of the two networks. Just connect the 3750 to it and set that link up as a trunk. You can then handle the routing on the test1 firewall.

If it is a 3750 or layer three switch then you can use my first comment to accomplish this.

On the 3750:

vlan 10
 name test2- network
vlan 20
 name test1- network

interface Vlan10
 ip address (or what ever IP is free on the subnet)
interface Vlan20
 ip address (or what ever IP is free on the subnet)
 ip dhcp-helper x.x.x.x (ip address of your DHCP server)
interface g0/"whatever number connects to test1"
 switchport mode access
 switchport access vlan 20

ip route
On the firewall you make a static route pointing /24 to

And you would detach the test1 firewall from the test1 switch so you use the firewall of test2
Also I would recommend not using network (unless you own them).

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