Layer 3 Switches, VLans and Multi Site

[KevinBugg]

Hi,

We are planning to implement vlans in our multi site organisation. We have a vpls network between sites and currently have cisco routers at each site for routing. However, we want to replace these with layer 3 switches and implement vlans with qos. Do you have to have a layer 3 switch at each end for it to work therefore all sites have to change at the same time to keep the network up and running or can you have a combination of layer 3 switchs and cisco routers? Im wasn't sure if they would be able to communicate and carry the qos between different devices.

Thanks
Kev

 

[ADB100]

Personally I would leave the routers in place (assuming they are capable of handling the throughput?) as you can configure much more granular QoS than on most of the Catalyst switches. You also have much more visibility of how your QoS policies are working. With most of the switches it can be difficult to see whats happening.

Use Layer-3 switches on your LAN where bandwidth is not usually an issue and then at your WAN edge implement the routers with your QoS policies. Have a read of the QoS SRND on CCO (

http://www.cisco.com/go/srnd)

HTH

Andy

 

[ADB100]

Just to add, implement QoS on your LAN switches with ingress edge marking policies on your access ports and queueing on all egress ports.

 

[VinceWhirlwind]

You probably don't have to have a layer 3 switch at each end for it to work and you can probably have a combination of layer 3 switches and cisco routers and your QoS will work.
It depends what routers you have. 1721s for example, you would throw in the bin, as they don't support VLANs.
On the whole, though, it will be easier to manage if you setup each site the same.
The important thing is to establish whether your VPLS provider supports classes-of-service and find out from them what tags they honour - They should offer you at least two classes offering EF and/or AF41 as well as "Best effort".
Then, you decide whether your voice devices should tag their own traffic (and configure the switches to "trust" that tagging) or you can configure the switches to re-mark on ingress all traffic depending on what IP address it comes from or what protocol it uses, etc....
Then, you will need to pass tagged traffic to the VPLS provider and then check that traffic at the remote site to see whether the tags have been stripped or not.

"show mls qos stats" (from memory).

 

[Viconsul]

^^Vince -- Cisco 1721 will support vlans and can still be used in a lab.

It depends what routers you have. 1721s for example, you would throw in the bin, as they don't support VLANs.

 

[VinceWhirlwind]

Ah, I must have remembered wrong.
I had a customer that had to throw out all their routers when implementing VoIP. On reflection it must have been 1720s.
I recall that any other router would support .1q & subinterfaces but not the ones they had, which was a bummer for them.

 

[ADB100]

I wouldn't use a 1721 to do inter-VLAN routing..... Performance?
Let your layer-3 switches route between your local VLANs and then connect your router(s) to a WAN handoff subnet, or even individual point-to-point subnets.

 

[Quadratic]

ABD100, true enough that router-on-a-stick is a legacy method of performing inter-vlan routing, but the question he's asking is whether or not they need to upgrade every site to L3 switches at the same time or if they can do it progressively. The answer is that he can do it progressively.

As for QoS, the VPLS provider will often overrite Ethernet CoS for their own use but preserve the IP ToS header (letting you control IP Precedence or DSCP). You'll have to confirm this with your provider.

CCNP, CCDP