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New Member

2 Switch stack Design for redundancy

Hi Everyone,

I need to connect 2 switches in stack which will connect to 2 servers.

Each server will habe 12 NICs.

So for Redundancy purposes i can connect 6 ports from server A to Switch 1

                                                               6 Ports from server A to Switch 2

Same way i can do

6 ports from Server B to Switch 1

6 ports from Server B to switch 2

IF i go with above design and in case say switch 2 dies then stack will have single switch will it cause any outage?

Regards

Mahesh

8 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Super Gold

2 Switch stack Design for redundancy

The Nexus solution will work on this scenario, Mahesh.

I wouldn't recommend the "traditional" 2960S/X, 3750/G/E/X, 3650 or 3850 because the interface buffers will get overwhelmed.

VIP Super Bronze

2 Switch stack Design for redundancy

Hi Mahesh,

What type of switch are you going to use?  If you use 3750X, LACP supports up to 16 ports, but the limit is 8 ports active and 8 ports on hot stand-by.  So, in your case the first 8 ports from the first server will be active and the other 4 will be on hot stand-by mode.  If you use the Nexus series switches, the limit is 16 with all 16 as active.

From your post, it apears you are using 3750s.

HTH

Reza

Highlighted
Cisco Employee

2 Switch stack Design for redundancy

Yeah, I would use 2x 10G adaptor and connect the server to a 10G switch using VPC for a better solution. This is an overkill. I would waste my my 24 ports switch just to address 1 server. What if I need to connect more devices..oh noo....Nexus is much better with 10G ports on host.

VIP Super Bronze

2 Switch stack Design for redundancy

  Hi Mahesh,

Ok, since you are using 3750G, than I am assuming these are all 1Gig copper interfaces. It will work, but you have to test the version of the IOS you have to see if it supports 16 ports with 8 active and 4 stand-by.  I did this with 3750X and it worked fine. I had a stack of 5 switches and each switch had 2 1Gig uplinks for a total of 10 ports all in one Portchannel.  So, 8 stayed active and 2 on stand-by.  When the ports are on stand-by, the light is orange and not green.  As soon as I pulled out one of the other 8 active cables, the 9th ports went active (green).

HTH

Reza

VIP Super Bronze

2 Switch stack Design for redundancy

Hi Mahesh,

No, since you are going to stack them, they are going to look as one switch (logically). So, out of 12 ports, 8 will be active and 4 stand-by.  Again, test with your switch and the IOS you are using to make sure it is supported because this is a new feature and was not available in earlier versions of IOS. In the earlier versions the max was 8.  If this is not supported by your IOS and/or switch, you would need to divide the ports and put 6 in one Portchannel and the other 6 in another Portchannel or 8 in one Portchannel and 4 in the other one.

The other solution would be instead of using all 12 NIC on the server, you just use 8 and put them all in one portchannel.

Ask the server guys if they really need that type of bandwidth with 12 NIC, because a lots of times 8 ports can be more than enough.

Reza

VIP Super Bronze

2 Switch stack Design for redundancy

Hi Mahesh,

So, I found this.  As long as you are running 12.2(25) or later verion you are good to go.

PAgP cannot be enabled on cross-stack EtherChannels while LACP is supported on cross-stack EtherChannels from Cisco IOS Software Release 12.2(25)SEC and later. Switch interfaces exchange LACP packets only with partner interfaces with the active or passive mode configuration. You can configure up to 16 ports to form a channel. Eight of the ports are in active mode, and the other eight are in standby mode. When any one of the active ports fails, a standby port becomes active. Interfaces with the on mode configuration do not exchange PAgP or LACP packets.

link:

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

HTH

Reza

Super Bronze

Re: 2 Switch stack Design for redundancy

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

IF i go with above design and in case say switch 2 dies then stack will have single switch will it cause any outage?

It depends.

One of your two switches will run in the role of switch master, and if that switch fails, there's a brief impact as control plane function are taken over by the second switch.  Whether this control plane switch over causes any impact to the server hosts depends on switch configuration and how (via L2 or L3) the hosts are communicating to other hosts.  For example, if you're running default, regarding master switch MAC persistence, that MAC will change, which I understand, will drop Etherchannel.

Silver

2 Switch stack Design for redundancy

Mahesh,

Now as you have issued the command the stack MAC address of the previous master will be used until you enter the

no stack-mac persistent timer command, which changes the stack MAC address to that of the current master. If you do not enter this command, the stack MAC address does not change and it will keep on working without any issues.

So the bundle should remain up.

Thanks

Ankur

"Please rate the post if found helpful"

13 REPLIES
Hall of Fame Super Gold

2 Switch stack Design for redundancy

The Nexus solution will work on this scenario, Mahesh.

I wouldn't recommend the "traditional" 2960S/X, 3750/G/E/X, 3650 or 3850 because the interface buffers will get overwhelmed.

Highlighted
Cisco Employee

2 Switch stack Design for redundancy

Yeah, I would use 2x 10G adaptor and connect the server to a 10G switch using VPC for a better solution. This is an overkill. I would waste my my 24 ports switch just to address 1 server. What if I need to connect more devices..oh noo....Nexus is much better with 10G ports on host.

VIP Super Bronze

2 Switch stack Design for redundancy

Hi Mahesh,

What type of switch are you going to use?  If you use 3750X, LACP supports up to 16 ports, but the limit is 8 ports active and 8 ports on hot stand-by.  So, in your case the first 8 ports from the first server will be active and the other 4 will be on hot stand-by mode.  If you use the Nexus series switches, the limit is 16 with all 16 as active.

From your post, it apears you are using 3750s.

HTH

Reza

New Member

2 Switch stack Design for redundancy

Hi REza,

I am using 3750G  switch which has 24 ports.

We are not using Nexus for now.

So will this work ok with 3750G  switch?

Regards

MAhesh

VIP Super Bronze

2 Switch stack Design for redundancy

  Hi Mahesh,

Ok, since you are using 3750G, than I am assuming these are all 1Gig copper interfaces. It will work, but you have to test the version of the IOS you have to see if it supports 16 ports with 8 active and 4 stand-by.  I did this with 3750X and it worked fine. I had a stack of 5 switches and each switch had 2 1Gig uplinks for a total of 10 ports all in one Portchannel.  So, 8 stayed active and 2 on stand-by.  When the ports are on stand-by, the light is orange and not green.  As soon as I pulled out one of the other 8 active cables, the 9th ports went active (green).

HTH

Reza

New Member

2 Switch stack Design for redundancy

Hi Reza,

So in my case each switch has 24 ports

so it means at one time each switch will have 6 active and 6 standby ports right?

Regards

MAhesh.

VIP Super Bronze

2 Switch stack Design for redundancy

Hi Mahesh,

No, since you are going to stack them, they are going to look as one switch (logically). So, out of 12 ports, 8 will be active and 4 stand-by.  Again, test with your switch and the IOS you are using to make sure it is supported because this is a new feature and was not available in earlier versions of IOS. In the earlier versions the max was 8.  If this is not supported by your IOS and/or switch, you would need to divide the ports and put 6 in one Portchannel and the other 6 in another Portchannel or 8 in one Portchannel and 4 in the other one.

The other solution would be instead of using all 12 NIC on the server, you just use 8 and put them all in one portchannel.

Ask the server guys if they really need that type of bandwidth with 12 NIC, because a lots of times 8 ports can be more than enough.

Reza

VIP Super Bronze

2 Switch stack Design for redundancy

Hi Mahesh,

So, I found this.  As long as you are running 12.2(25) or later verion you are good to go.

PAgP cannot be enabled on cross-stack EtherChannels while LACP is supported on cross-stack EtherChannels from Cisco IOS Software Release 12.2(25)SEC and later. Switch interfaces exchange LACP packets only with partner interfaces with the active or passive mode configuration. You can configure up to 16 ports to form a channel. Eight of the ports are in active mode, and the other eight are in standby mode. When any one of the active ports fails, a standby port becomes active. Interfaces with the on mode configuration do not exchange PAgP or LACP packets.

link:

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

HTH

Reza

New Member

2 Switch stack Design for redundancy

Hi Reza,

Switches are stacked up now just final config has to be put there.

Many thanks for the valuable info.

Regards

MAhesh

Super Bronze

Re: 2 Switch stack Design for redundancy

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

IF i go with above design and in case say switch 2 dies then stack will have single switch will it cause any outage?

It depends.

One of your two switches will run in the role of switch master, and if that switch fails, there's a brief impact as control plane function are taken over by the second switch.  Whether this control plane switch over causes any impact to the server hosts depends on switch configuration and how (via L2 or L3) the hosts are communicating to other hosts.  For example, if you're running default, regarding master switch MAC persistence, that MAC will change, which I understand, will drop Etherchannel.

New Member

2 Switch stack Design for redundancy

Hi,

IOS we are using is lastes as per cisco 150 something.

Mostly we will be using layer 2 ports  with servers.

If we use Etherchannel Layer 2 bundles from switch to servers  and if i configure command

stack-mac persistent timer 0 and now if master switch dies there will be no impact right all etherchannel bundles should remain up?

Regards

MAhesh

Silver

2 Switch stack Design for redundancy

Mahesh,

Now as you have issued the command the stack MAC address of the previous master will be used until you enter the

no stack-mac persistent timer command, which changes the stack MAC address to that of the current master. If you do not enter this command, the stack MAC address does not change and it will keep on working without any issues.

So the bundle should remain up.

Thanks

Ankur

"Please rate the post if found helpful"

New Member

2 Switch stack Design for redundancy

Many thanks Ankur

Mahesh

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