VLAN & Internet Access

[rsabapathee]

Guys,

My network has 2 VLANs at the moment, planning to add more.Lets say for now vlan 1 & 2. My internet router is found in VLAN 1. Inter-VLAN routing has been configured on a Cisco 1710 and works fine in our network.

1) How to make those in VLAN 2 access the internet through ADSL router in VLAN 1? What ip route to configure?

(Just a quick note, some other ports we should enable for internet access: pop3 110, smtp 25)

2) Would it be easier to shift the ADSL router to a different VLAN as I add vlan 3, 4 ,etc?

rgs

roghen

[Anand Narayana]

Hi,

In ADSL router you need to specify route "192.168.2.0 255.255.255.0 192.168.1.1" same for vlan 3 route "192.168.3.0 255.255.255.0 192.168.1.1"

hope this helps.

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[Richard Burts]

The statement that no routing is needed in the ADSL router is bad advice and is not true. The ADSL router certainly does need to do some routing. No doubt the ADSL router has a default route pointing out into the Internet. And the ADSL router has in interface in network 192.168.1.0 so it can route to that network. But how will the ADSL router get to the network in VLAN 2 which is 192.168.2.0? The ADSL router must have a route identifying that 192.168.2.0 is reachable through the address on the 1710.

HTH

Rick

[rsabapathee]

What happens to VLAN 2 broadcast when I add the route described above? Will it be forwarded to VLAN 1?

ip route 0.0.0.0 0.0.0.0 192.168.1.26 ??

[Richard Burts]

Roghen

The VLAN 2 broadcasts are not forwarded to VLAN 1. One of the principles of layer 3 routing is that it establishes a boundary for layer 2 broadcasts. So any broadcast in VLAN 2 is forwarded to every device in VLAN 2 but is not forwarded to any device in VLAN 1.

If you did want broadcasts to be forwarded there is the ip helper-address command which can forward some broadcasts. But by default there is not forwarding of broadcasts from one VLAN to another VLAN.

HTH

Rick