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Community Member

VLAN communication in between WAN.

Hi,

I have 2 Routers are connected in WAN like R1 and R2. Both having 3 VLANs,like VLAN 1, VLAN 2an VLAN 3.Am using OSPF for routing in both routers.And for inter VLAN communication happends through the FastEthernet of Router,which is connected with switch.

here my question is that how will be the communication between VLANs (eg: R1 VLAN 1 <==> R2 VLAN 1)...? is it possibile...?

-Siyadh

8 REPLIES
Hall of Fame Super Blue

Re: VLAN communication in between WAN.

siyadh2020 wrote:

Hi,

I have 2 Routers are connected in WAN like R1 and R2. Both having 3 VLANs,like VLAN 1, VLAN 2an VLAN 3.Am using OSPF for routing in both routers.And for inter VLAN communication happends through the FastEthernet of Router,which is connected with switch.

here my question is that how will be the communication between VLANs (eg: R1 VLAN 1 <==> R2 VLAN 1)...? is it possibile...?

-Siyadh


Siyadh

If vlan 1 on R1 and vlan 1 on R2 are both usiing the same IP addressing/subnet then no they won't be able to communicate across a routed link. If the vlan number was the same but the IP subnet different then you would be fine.

If you need the vlan 1 to use the same subnet on both routers then you can L2TPv3 which allows you to extend a L2 vlan across a L3 routed link -

http://www.cisco.com/en/US/customer/docs/ios/12_3t/12_3t2/feature/guide/gtl2tpv3.html

Do you actually need them to be the same subnet ?

Jon

Community Member

Re: VLAN communication in between WAN.

Thanks Jon,

We cannot use same IP addressing/subnet in both Routers,am i rit...? So it should be different subnet.

But again one more important thing is that for both subnet the IPs produced from single DHCP server, which is located in either R1 or R2 place.

Siyadh.

Re: VLAN communication in between WAN.

That's not a problem, you can place the DHCP server in the back of R1, and have R2 forward the DHCP requests coming from it's LAN clients to DHCP server.

You just have to configure on R2 interface facing LAN, ip helper-address IP_DHCP_SERVER


Of course, R2 should know how to reach IP_DHCP_SERVER.

Cheers,

Calin

Community Member

Re: VLAN communication in between WAN.

Calin,

So let me conclude this topic as below:

1. Configured both router with OSPF (R1 & R2).

2. Each router has 3 VLANs (VLAN 1,VLAN 2 & VLAN 3 ).

3. ip helper-address IP_DHCP_SERVER will provide the IPs to all the systems ( both locations).

4. Each router will do the Inter VLAN routing,the IPs which is under the same router (FastEthernet port of both Router with SubInterface).

Am i rit...?

-Siyadh.

Re: VLAN communication in between WAN.

Here it is:

1. Correct

2. 3 SVI (L3 vlan interfaces) with IP address that will be the gateway for clients in VLAN 1 (I would suggest not to use VLAN 1, due to its default native status), For example, you have clients in VLAN 2, then you have to configure interface vlan 2, with an IP adress of 192.168.0.1 netmask 255.255.255.0, and all the clients in VLAN 2 will have IP addresses from 192.168.0.2 - 254 with gateway on 192.168.0.1 (IP addresses are just example to understand better). This subnet has to be advertised into OSPF. Also the subnet has to be configured in your DHCP server if you want dynamic IP allocation

3. ip helper-address IP_DHCP_SERVER has to be configured only on the oposite side where your DHCP server is located. For example, if your server is behind R1 in the LAN, then you need to configure this command only on R2 interface facing LAN (e.g. interface vlan 2)

4. Exchange information for hosts on different VLANs will be done at L3 on the router side.

Cheers,

Calin

Community Member

Re: VLAN communication in between WAN.

Thank you Calin.

This helps me a lot.

-Siyadh.

Re: VLAN communication in between WAN.

Hello Siyadh,

If I understood correctly, you have 2 routers interconnected over a WAN connection. In this case you need to use a QinQ technology to be able to allow communication to devices in the same VLAN. QinQ preserves original VLAN tag in communication over WAN. This is if you want to avoid routing and you really need to have devices in the same VLAN.


Be aware that QinQ is not supported on all devices. You need a L2/L3 switch to support QinQ. For me it's a little bit confusing because you said that you have 2 routers and then you add that each has VLANs. From my knowledge only routers with swich cards (e.g. Cisco 3725, Cisco 3640) support VLAN configuration. So, what devices you have there exactly?

If you still want to go on with QinQ, here is an example how you have to configure it:

http://www.cisco.com/en/US/docs/ios/lanswitch/configuration/guide/lsw_ieee_802.1q.html

If you want a solution that is more simple to achieve: use routing. You have some clients with network subnets in the back of R1, then some clients with (another) network subnet in the back of R2. Then you establish a dynamic routing protocol between R1 and R2 (I see you already did this with OSPF) and advertise the LAN subnets into this routing protocol. In this way you assure communication between LAN's devices.

Let me know if this helps or you had something different in your mind. Some more details would help!

Cheers,

Calin

Community Member

Re: VLAN communication in between WAN.

Thank you Calin,

I could find the solution in QinQ technology.thank you for this information.

And 1800 router will support interVLAN routing.

- Siyadh

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