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design/performance question

Good Day,

This question involves wireless, but I think it is fundamentally one of switching.

I manage the network in a large college residence hall. At present, the resident rooms are connected through wired connections to 2 6509s (sup2 layer 2 only).

Each 6509 is configured for three vlans which are trunked to a 2960G-24TC-L located in a central wiring closet where the six are trunked together on out to campus.

We are rolling out a wireless network that will involve approx 20 aps connetcted to each 6509. We will be using a WLC 4402 (2 gig ports)to manage the wirless and this is located in the central closet with the 2960G-24TC-L .

Because we have extra fiber runs from each 6509 to the central wiring closet, I can connect the WLC directly to each of the 6509s and thereby localize the traffic between the ap's and the WLC. Allowing the 6509s to do the "heavy lifting" here appeals to me as it distributes the load between several devices.

On the other hand, simply adding the vlan carrying the traffic between the ap's and the wlc to the existing trunk ports between the 6509s and the 2960G and then connecting the WLC to the 2960G has the appeal of simplicity.

So the crux of the question would be whether I would see an decline in perfomance, or any other downside, by adding the traffic between the WLC and 40 ap's with up to 450 wireless clients to the load on the 2960G (forwarding rate 35.7 mpps)

thanks

1 REPLY
Hall of Fame Super Silver

Re: design/performance question

Hello Bill,

here is a link to best practices for WLC 4400

http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a0080810880.shtml#topic2

be aware that if you use LWAPP L3 encapsulation you will need multiple vlans:

one management to reach the APs and some clients VLans: in your case you could use 1 mgmt vlan and 3 clients vlans

having 40 APs and 450 users all in the same IP subnet can be a problem with the level of broadcast traffic that can reduce performances (wireless lan is not full duplex)

on the other end if you use L3 encapsulation you need some L3 device to perform routing to client vlans

the client vlans with L3 encapsulation are not seen on the wired L2 switches but are terminated directly at the distribution layer

We have a campus with 160 APs using L3 LWAPP with WISM WLCs the WLC modules for C6500.

Being your C6500 switches layer2 only you can have the management vlans on the fiber links the AP that encapsulate client packets into LWAPP IP packets to /from the controller

But the controller needs also to connect to the core/distribution for example to provide internet access to wireless users

About just adding the vlan between APs and WLC to C2960 you can take a network baseline of current usage over one week using tools like MRTG or other to understand if the 2960 has enough resources to support the wireless lan traffic of APs and end users.

Probably it is better to offload using the additional fibers in order to leave the 2960 for the wired access.

A mixed way could be that of using the 2960 as a L2 device for the new Vlan terminating on the core (no L3 services on the 2960) but this would require to extend l2 topology to the core and you probably have L3 links to the core from 2960.

Hope to help

Giuseppe

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