Catalyst 3524XL : mixing multi-VLAN and VLAN trunk

[6mmagenc]

A customer has a Catalyst 3524 XL with 3 "administrative" VLANs (let's call them Red,Blue,Green) and 2 multi-VLAN ports which both belong to VLANs Red,Blue and Green.

* On each multi-VLAN port an IP router is connected.

* On each VLAN port a station or server is connected.

* All routers, stations and servers run IP and have IP addresses into the SAME IP network (no subnet).

* All stations and servers use both routers.

This works well. Now, the customer bought another 3524XL in order to extend his LAN. He wants to interconnect both switches, have ports belonging to the 3 existing VLANs on both switches, allow any station or server to use both routers , and does'nt want to change the IP addressing scheme.

How could this achieved ?

Using a trunk (ISL or 802.1Q) between the switches is not compatible with having a multi-VLAN port AND a trunk port on the same switch .

If the routers support 802.1Q trunking, would it be possible to replace multi-VLANs ports by 802.1Q trunk ports between switch and router ? If so, how would such a router know the way it would tag frames whose destinations may be MACs belonging to any of the 3 "administrative" VLANs ?

Thanks in advance for any input.

Best regards, Michèle .

[ssymonds]

Hello Michele,

Apart from creating dedicated ports on each switch, for each VLAN, then cabling individual VLANs between switches (not exactly a scaleable solution) ...I cant think of any other options to acheive this requirement (without trunking or changing the IP addressing).

As you have suggested, a recommended option would to configure trunking between switches and the routers. In this case, you would need to configure a subnet per VLAN (in this way the router knows which MAC belongs to which VLAN ... i.e a L3 destination address corresponds to a VLAN, and ARP broadcast / response discovers MAC addr ). In this instance, ensure that the router can handle required levels of 'inter-subnet' traffic requirements (depends upon traffic characteristics).

rgds

steve