Using Catalyst 3560/3750 in a WAN/MAN environment & QoS?

Unanswered Question
Jun 20th, 2008

Generally if strict QoS control is required in a WAN/MAN environment I would recommend 'real' routers (2800, 3700 etc). The reason being is you can apply ingress & egress QoS policies to strictly control the traffic and ensure SLA's are adhered to etc. Ethernet WAN services are now cheaply available so most customers get 10 or 100Mbps LES circuits instead of traditional WAN links (like 2Mbps E1 links etc). Since a LAN switch will inevitably be purchased to support LAN clients many customers want to simply terminate the Ethernet WAN onto the switch (typically a 3560 or 3750) to avoid the additional cost of a router. Even with the IP Base image on a Catalyst 3560 we can route over a LES circuit,the 3560 effectively being a 'router'. Generally this is fine as we can strictly queue any VoIP using the strict-priority queue, however if anything more 'clever' is required we are a bit stuck since this platform doesn't support egress QoS policies; just queueing based on DSCP or CoS.

If anything more clever is required a 'real' router will do the trick and I would generally recommend this option. Unfortunately even a 2800 will struggle with a 10Mbps link that was highly utilised (if it was hit with lots of small packets). A Catalyst 3560 would easily cope with this traffic though? Which has caused a bit of a dilema.

I hope I have explained the dilema and am after other peoples solutions/ideas.



I have this problem too.
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Edison Ortiz Mon, 06/23/2008 - 11:20

10Mbps WAN connection on a 3560 should be fine.

Think of this way, would you ask that question if you were uplinking this 3560 to a Core switch at 10Mbps? :)

The QoS limitation is the deal breaker for placing this switch as a WAN switch, but you know that already.



andrew.butterworth Mon, 06/23/2008 - 11:34

Thanks for the reply Edison. You are correct; there would be no dilema if the 3560 was just an access switch in a campus, however the traffic patterns between a WAN Aggregation switch/router and a Campus Access switch are typically much different. In the WAN we ideally want as much control of the bandwidth as possible, in the LAN its not usually a big deal.

My issue is if we want to put a router on the WAN circuit (10 or 100Mbps Ethernet) then we need a pretty powerful router - it is looking like 3800 sized boxes which is going to get expensive. A Cat 3560 won't have any issues with these forwarding rates, however we loose some control through not having the QoS features available....


Edison Ortiz Mon, 06/23/2008 - 11:38

however the traffic patterns between a WAN Aggregation switch/router and a Campus Access switch are typically much different

Correct. That's the reason you never see a 3560 as a WAN switch. Not because the transfer rate will overwhelm the switch, but because the limitation on other features/services (QoS, for instance).

I see this dilemma all the time. You now see these switches that can almost do anything at a reasonable price until you hit the QoS wall :)



Collin Clark Mon, 06/23/2008 - 12:51

What about the 3560-E or ME series switches? I thought they (especially the Metro Ethernet) provided enhanced QoS features (still downloading the QoS SRND).

andrew.butterworth Mon, 06/23/2008 - 13:13

I have looked into this before and the Metro 3750 has two Enhanced Services SFP ports that you can apply egress service-policies on, so it looks like it should work. Unfortunately the ES ports only operate at 1Gbps, unlike the 'regular' SFP ports that can work at 10/100/1000 depending on the installed SFP.

If the ES ports worked at 10/100/1000 then this would be an option, however there are only two per switch, plus the Metro 3750 isn't stackable (it has the stack ports but they are not functional apparently?)


andrew.butterworth Tue, 06/24/2008 - 01:10

I hadn't noticed the other Metro switches before (ME 3400 & ME 2400). Looking at the documentation it states:

'If the switch is running the metro base or metro access image, only four ports on the switch can be configured as NNIs at one time, but all ports on the switch can be configured as UNIs or ENIs. Starting with Cisco IOS release 12.2(25)SEG, if the switch is running the metro IP access image, there is no limit to the number of NNIs that can be configured on the switch.'

So we could have a 24-port 10/100 Metro switch (ME-3400-24TS-A) with the IP Access IOS image with all ports doing what we want? This is a bit more expensive than a 24-port 10/100 3560 (about $2k) however its cheaper than a router plus interfaces.

If anyone has any experience with the ME 3400 I would be grateful of any experiences?



Joseph W. Doherty Mon, 06/23/2008 - 19:44

". . . have explained the dilema and am after other peoples solutions/ideas."

Since there's no "inexpensive" totally integrated Cisco routing platform that offers high (e.g. gig and better) L3 bandwidth and full IOS feature richness, I sometimes suggest using both a "small" L3 switch (or EtherSwitch Service Module) and a "right sized" software router.

My experience with the "little" routers, e.g. 2800 series, can handle multiple "increments" of 10 Mbps bandwidth. Assuming a 100 Mbps WAN handoff isn't really providing the full 100 Mbps capacity and assuming any local LAN routing is being handled by a L3 switch, using the combo of L3 switch and small router often works well at an attractive price point vs. larger router. E.g. the 1841 or 28xx and 3560/3750, or 28xx (2811 or higher) with a EtherSwitch Service Module, etc., vs. 3800 or 7200 used for both LAN and WAN routing.

As the WAN bandwidth increases, you either need to up the WAN router model to match the capacity, or do away with the WAN router and rely just on the L3 switch. Of course, you lose features having just the L3 switch, but the additional WAN bandwidth, hopefully, negates the features need as some of the latest application/WAN accelerators might too.


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