Help with VSS Design

Answered Question
Aug 18th, 2010

Hi Team

I need your help with the following design:

Right now we are working in a design for one of our customers, and we want to offer them 2 6504-E, with the Virtual Switching Technology.

These are the components:

-    (2) Switches 6504-E, each switch includes: (1) VS-S720-10G-3C and (1) WS-X6708-10G-3C
-    (9) Switches WS-C3750X-24P-L

The 9 3750X Switches are going to be divided in 3 groups of 3 Switches 3750X(see attached diagram). We want to stack the 3 3750X Switches using the Stackwise technology that these switches support.

Like the diagram shows, we also want to connect the first 3750X of each group to VSS Switch 1, and the last 3750X of each group to VSS Switch 2. The connection will be using the WS-X6708-10G-3C cards.

The idea is to have redundancy using Multichassis Etherchannel (MEC), from the VSS Switch 1 and VSS Switch 2 to the Switches in the stack. Is possible to have this type of redundancy? If VSS Switch 1 or the first switch in the stack fails, then VSS Switch 2 will keep communication with the last switch of the stack.

If you have any comments or suggestions, please let me know.

Thanks a lot for your help.

Regards,

Annya

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Correct Answer by Giuseppe Larosa about 3 years 8 months ago

Hello Annya,

LACP is supported on the cross stack etherchannel

Actually also PAGP is supported, what is not supported is Enhanced PAGP that would be required to implement dual active detection with the help of a third party switch.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/vss.html#wp1063735

As I wrote in my previous post I prefer to have a dedicated direct link between the two VSS members rather then relying on a third party switch.

In your case if PAGP+ is not supported on the C3750X you need to use BFD or fast hello

PAGP and LACP are both supported in C3750 stacks, but LACP can be preferred as being standard based

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_53_se/configuration/guide/swethchl.html#wpxref31717

see the section named etherchannels and stacks

Hope to help

Giuseppe

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Giuseppe Larosa Wed, 08/18/2010 - 08:50

Hello Annya,

the proposed design can work as C3750 stacks support cross stack etherchannels that are similar to MEC on VSS so the connections can work as intended.

my personal opinion is that however, for dual active detection I would use dedicated links on the two C6500 chassis instead or relying on PAGP+ on the MEC.

You need to provide for dual active detection on VSS that has to be avoided you can use simple GE links for this and not 10GE ports.

These links are different from those used for the VSL bundle.

you can use BFD on one additional GE link and IP fast hellos on a second additional link.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/vss.html#wp1063892

Hope to help

Giuseppe

annya.martinez Wed, 08/18/2010 - 10:09

Thanks Giuseppe for your quick response.

Excellent suggestion, we will add another link between the 2 C6500 using BFD or Fast Hello.

My doubt is about providing redundancy to the access layer, that is composed of 3 group of 3-Stacked C3750 Switches, using MEC. Will both links seen as one (20GE), even if those links come from 2 different stacked C3750 Switches using MEC to VSS Switch 1 and VSS Switch 2?  I was reading that there are some features that are not supported on the 3750 Switches in stack, for example PagP is not supported in the cross-stack. Could this affect the solution that we want to offer?

Thanks,

Annya


Correct Answer
Giuseppe Larosa Wed, 08/18/2010 - 12:08

Hello Annya,

LACP is supported on the cross stack etherchannel

Actually also PAGP is supported, what is not supported is Enhanced PAGP that would be required to implement dual active detection with the help of a third party switch.

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/vss.html#wp1063735

As I wrote in my previous post I prefer to have a dedicated direct link between the two VSS members rather then relying on a third party switch.

In your case if PAGP+ is not supported on the C3750X you need to use BFD or fast hello

PAGP and LACP are both supported in C3750 stacks, but LACP can be preferred as being standard based

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_53_se/configuration/guide/swethchl.html#wpxref31717

see the section named etherchannels and stacks

Hope to help

Giuseppe

SaeedBakh_2 Fri, 09/10/2010 - 05:29

hI ,

we are planning to have two 6509E with VSS and firewall and ACE modules, and the access switch we have 3COM switches support LACP can we have MEC between the 3com access switch and the two 6509EVSS core.

Regards

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Posted August 18, 2010 at 8:39 AM
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