wan connection

[#1]

HI All,

I have some network experience, which is mainly L2. I have a BT Business broadband line and I would like to use a 3750 L3 switch to create multiple vlans with the routing and use the BT line as the internet connection with the default route pointing to the BT Hub. The BT hub from what I have read will not support NATing for the vlans and I would require a router that would. I have a spare Cisco 1800 router with an adsl port on it but not sure if this is suitable so I am looking for some general advise. Would the 1800 be suitable for my needs and would I place it between the BT hub and the L3 swtich or replace the BT altogther. Apologies for the vagueness of the question.

Many thanks in advance

Gary

[Julio E. Moisa]

Hi Gary,

Yes, your scheme should work: Switch - Router - ISP.

The router, firewalls and some switches like 6500 support NAT, you should configure the following on the router, not sure how is represented the ASDL interface but we will take dialer 1 as reference

interface dialer 1
description TO-ISP
ip nat outside

interface g0/1   
description TO-SW
ip nat inside

ip access-list standard PRIVATE-NETS
permit 192.168.0.0 0.0.0.255
permit 192.168.1.0 0.0.0.255
permit 192.168.2.0 0.0.0.255
.
:
:

ip nat inside source list PRIVATE-NETS interface dialer 1

ip route 0.0.0.0 0.0.0.0 <ISP IP next hop> name TO-INTERNET

ip route 192.168.0.0  255.255.255.255 <IP of Switch - Point-to-Point>
ip route 192.168.1.0  255.255.255.255 <IP of Switch - Point-to-Point>
ip route 192.168.2.0  255.255.255.255 <IP of Switch - Point-to-Point>

On the switch if you are using the 3750 as Layer 3, you should create a default route pointing to the router. 

Hope it is useful

:-)

[#3]

Hi Julio,

Many thanks for the advice! I may pick your brains again if possible. I will give this a go and let you know. It might be a few days before I get onto it though.

Many thanks and kind regards

Gary

[Julio E. Moisa]

Hi Gary,

You are welcome, remember to enable ip routing on the 3750 switch to support static routing or routing protocols. 

It should be like:

Switch

ip routing

interface f1/0/24
description TO-ROUTER
no switchport
ip address <IP address / subnet mask - Point to Point with Router>

ip route 0.0.0.0 0.0.0.0 <next hop IP (Router Interface)

:-)

[Joseph W. Doherty]

A small router might be suitable for your NATing needs, although they usually only have capacity for low bandwidth (compared to LAN bandwidths).  If such a router doesn't have two Ethernet ports, you might be able to trunk it to your L3 switch, and provide an "external" VLAN for your BT hub connection.