Cross-Stack 10-Gigabit EtherChannel on 3750E/3750-X/2960-S

[shillings]

According to the following Cisco webpage, cross-stack 10-Gigabit EtherChannel is possible on the 3750 with up to two 10-Gigabit modules, using LACP: http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_example09186a00806cb982.shtmlhttp://

However, the webpage doesn't confirm if this functionality is restricted to a particular 3750 model, such as 3750E, or if it applies to all models. It also doesn't specify any particular IOS feature set. I've tried Cisco Software Advisor but it doesn't list this feature on either the 3750E or 3750-X. Can anyone help?

Next question, does anyone know if this is possible on the 2960-S switches (i.e. cross-stack 10gig EtherChannel)?

[johnnylingo]

Once a stack is created, both sides only "see" one switch, so Cross-Stacking doesn't require any additional configuration.  If your switch supports PAgP or LACP, you should be good to go.

[shillings]

Thanks Johnny.

Pretty sure PAgP doesn't support the 'cross-stack' element though, unless Cisco has added it recently.

[johnnylingo]

Yes, looks like it.  I do not know why LACP and PAgP would be different to stacking, but that's what the doc says:

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_example09186a00806cb982.shtml#lacp

[shillings]

Since confirmed via Cisco webpage that the 2960-S can do cross-stack EtherChannel, but it doesn't say if it can do 10-Gigabit EtherChannel, or just 1Gbps.

Still can't find out if the model or feature set is important on the 3750 product.

[shillings]

Our Cisco distribution partner has confirmed that cross-stack 10-Gigabit EtherChannel is compatible with 3750E, 3750-X and 2960-S. They said it is not dependant upon the IOS feature set, so IP Base (3750) and LAN Base (2960-S) will both work fine.

[Leo Laohoo]

Confirm that you can configure Etherchannel on multiple 1Gbps OR 10 Gbps links from a stacked 2960S to a stacked 3750E/3750X.  IOS version or feature set not important.

Whether or not a stacked 2960S can push 10Gbps or not is another question. 

[shillings]

Thanks leolaohoo.

Ref the 2960-S pushing 10Gbps, it has a forwarding bandwidth of 88Gbps (half duplex), so do you mean the FlexStack technology for linking them?

If so, the FlexStack data sheet says they can push 10Gbps and another 10Gbps in the opposite direction. I guess I need to get my head around the FlexStack data flow, but any tips/hints are very welcome ;o)

[Leo Laohoo · Accepted solution]

Ref the 2960-S pushing 10Gbps, it has a forwarding bandwidth of 88Gbps (half duplex), so do you mean the FlexStack technology for linking them?

The FlexStack can push 10 Gbps, full duplex.  SO you if have, say three 10 Gbps links then the other two would be beneficial if you consider it as a backup link only.  If you plan to use it to aggregate the links to push >10Gbps data down then it's a waste of money.

[shillings]

OK, thanks.

I thought maybe a 2975 would do instead of the 2960-S, but no 10Gbps connectivity looking at the data sheet.

More 3750s then!

[shillings]

I've been re-reading the data sheet and giving this more thought.

To quickly summarise, I want to use cross-stack 10-Gigabit EtherChannel between two stacked 3750s and two stacked 2960-S switches - i.e.run two 10Gbps fibre uplinks between the two stack pairs.

The 2960-S data sheet suggests a stacked pair of 2960-S switches can have two FlexStack 10Gbps connections between them with each FlexStack connection running at full duplex. To my mind, this suggests 20Gbps (2 x 10Gbps) is feasible because there are two FlexStack links, and not just 10Gbps as previously suggested.

However, I wonder if FlexStack would even need to push more than 10Gbps in my scenario. Let's say 10Gbps of traffic ingress switch 'A' via normal 1Gbps switchports. Switch 'A' has its own 10Gbps fibre uplink to a directly connected 3750, so whilst EtherChannel load balancing may attempt to send some sessions via the FlexStack module to Switch 'B', the remaining sessions can simply egress the local 2960-S via its 10Gbps uplink to a directly connected 3750.

And the same for Switch 'B' if it has another 10Gbps of ingress traffic via normal switchports. This would mean the FlexStack module would only ever see 10Gbps, because the EtherChannel load balancing would send the other 10Gbps via locally connected fibre uplinks to 3750s.

The data sheet says FlexStack is based on 'Stackwise Plus' (not 'Stackwise'), so in therery it can switch across the local fabric without needing to utilise the FlexStack module for all traffic.

Thoughts anyone?

[Leo Laohoo]

The 2960-S data sheet suggests a stacked pair of 2960-S switches can have two FlexStack 10Gbps connections between them with each FlexStack connection running at full duplex. To my mind, this suggests 20Gbps (2 x 10Gbps) is feasible because there are two FlexStack links, and not just 10Gbps as previously suggested.

Unless specified, the so-called "20 Gbps" is expressed in, surprise, HALF duplex.

[shillings]

I don't understand how two 10Gbps full duplex StackWise connections can be viewed that way.

The FlexStack page say this:

A single FlexStack connection between two members is a full duplex 10Gbps connecton. Each Cisco Catalyst 2960-S member supports two FlexStack connections. Each FlexStack member can simultaneously send and receive Ethernet traffic over both stack links at line rate, effectively giving 20Gbps of stack bandwidth per member.

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/white_paper_c11-578928.html

[Leo Laohoo]

I don't understand how two 10Gbps full duplex StackWise connections can be viewed that way.

You mean the statement of "20 Gbps" is not being specified as half or full duplex?

[shillings]

leolaohoo wrote:
I don't understand how two 10Gbps full duplex StackWise connections can be viewed that way.
You mean the statement of "20 Gbps" is not being specified as half or full duplex?

I mean that Cisco state full duplex, so why do you think half duplex?

Agreed it's not a single 20Gbps full duplex connection, but instead, a pair of 10Gbps full duplex connections.

Either way, I still wonder if just 10Gbps full duplex is sufficient for the scenario in question.