Switch Stack or HSRP

[ciscobigcat]

Hi guys,

I just inhereted a network which has 7 switches (3750s) as a Stack. In there, there are 5 SVI (switch virtual interfaces) and in each of these VLANs, HSRP is configured.

Question:

• Is HSRP really needed in a Stack configuration?
• If so, what are the benefits?
• Can I simply clean-up the config and remove HSRP?

Thank you

[Thotsaphon Lueangwattanaphong · Accepted solution]

Hi,

Q: Is HSRP really needed in a Stack configuration?

A: No, HSRP is not a part of configuration to build the stack

Cisco StackWise and StackWise Plus Technology Ref: http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps5023/prod_white_paper09186a00801b096a.html

Q: If so, what are the benefits?

A: HSRP is a protocol that is used for gateway redundancy. Let's say you have 2 switches(gateway for users) you want those switches acting as active/standby for users then you can use HSRP. 

HSRP Ref: http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a91.shtml

Q: Can I simply clean-up the config and remove HSRP?

A: If you don't want to use it. You can remove it.

HTH,

Toshi

[Mohamed Sobair · Accepted solution]

Hi,

With Stacking, you actually eleminate the need of first Hop redundancy protocols, and yes , there is no benefit and you can safely remove it, unless otherwise you have some Switches or routers connected to the Stack and you need this feature.

but , with the Stack alone, you dont need the first hop redundancy protocols.

HTH

Mohamed

[ciscobigcat]

Toshi, Mohamed,

thank you both for the input. This is very helpful to me. I have very basic knowledge about Cisco so this is why I ask the big cats.

There are many things on this network I just inhereted that are not in place and also many unneeded things like this HSRP protocol configured within a stack.

The network is just a plain network. One single stack of 7 switches and one ASA5500 connected to it with is the gateway to the internet. Nothing else.

I will now implement the clean-ups and I also need to add another switch to this stack. What do you guys recommend is the best way to do this? Before, I've tried to just add new swtiches to a stack but had a lot of problems. I then had to just manually number the new switches and that was the only way I was able to successfully add them. But again, I'd like to know what is the best and recommended way of doing this?

Regarding the HRSP and Stack again, I now feel a lot more comfortable with my initial thoughts thanks to your input. I understand now that if I had a switch connected to this stack, then it will then make sense to use the HSRP protocol since the assumption will be if the stack goes down (yes, all 7 or 8 switches ) this switch will take over... correct?

thank you

[Thotsaphon Lueangwattanaphong]

Hi,

   you can think of all switches in the stack is the only one switch. If you want to do gateway redundany with the new switch and the stack switches, yes you can use HSRP.  However, I'd add a new 3750 into the stack instead.

HTH,

Toshi

[Mohamed Sobair]

Hi,

According to the DataSheet of the Catalyst 3750. you can add up to 9 Switches in the Stack, However, I am not quite sure about the impact (If there is any) or performance if you have such number or more than 7 switches in the Stack.

Here is the link to the DataSheet:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps5023/product_data_sheet0900aecd80371991.html

Anyway, adding a new switch member to the Stack is easy, you need to make sure it has the lower priority than the Stack master, the default priority is 1 and your Stack should normally have a priority of 15 which is the maximum. Power Off the Switch, connect the Stack Cable to the Stack member, power On the Switch and you should be fine.

if you have another Switches that needs to be connected to the Stack other than 3750, for example if you need to add them to a distribution layer, its recommended not to connect them to the stack master directly and not envolve the Stack master, you just uplink it through any other member of the Stack swirtches.

I hope this Helps,

Mohamed

[Leo Laohoo]

If you have stack switches and HSRP then consider using HSRP when you have TWO stacks.  Consider a stack of switches as a single logical unit (that's what the switches see).

Now you mentioned that you have a stack of seven???  I am going to say that this is one method I don't recommend.  I've seen issues when you use more than 6 switches in a stack. 

[ciscobigcat]

what are the problems you have seen in a stack of more than 6 switches? As I mentioned, this stack has 7 switches and I have been given another switch to add it to the stack.

For the HSRP thing, I think I am now 100%. HRSP does not have to do anything when there is a single stack. I heard today that the old IT admin was fired and this is why I got called.... I'm humble and told the customer I work closely with TAC and this forum and they had no problems  

Every doubt I have I run it thru here or TAC. So as for the HSRP I have no idea why the old ITs had it configured when this has always been a stack.

So really, I'd like to know the vote to add this 8th switch to the stack... for the ones against it, again why is this? what is the disadvantage? will I see a performance hit? what is going to happen?

As for the question again on how to properly add a switch to a stack, I'd like to get deeper and find out the exact details, from the licensing, to the IOS version to the final preparation of the new switch. Can you guys also help with the commands?

Today I also heard that before they let go the old IT, they had purchased 2 new switches and those were added to the stack however they have temp licenses. I was given a bunch of email chains that I have to follow where they told I should be able to find the permanent license they purchased for these last 2 switches that were added to the stack... so I guess it was a stack of five and they added 2 more which are still running with temp licenses and now they purchased another one.

So please bear with me until I complete this thing 

thank you  

[Leo Laohoo · Accepted solution]

During those days when we have to configure a full stack of 9, we would experience lag.  IT gets worst when we configure the interface range command.  Boy, it's a heart-stopping lag.  When we pulled the stack down to 6 in a stack, things get a wee bit better.

Another thing is the backplane.  Depending on what you have, 16 or 32 Gb half-duplex backplane, you want to enjoy the benefit with the least amount of switches in a stack not more.

As for the question again on how to properly add a switch to a stack, I'd like to get deeper and find out the exact details, from the licensing, to the IOS version to the final preparation of the new switch. Can you guys also help with the commands?

1.  Make sure the new switch has the the same IOS version and feature as the stack.

2.  Before adding the new switch, use the "provision switch" command, make the necessary port configurations before proceeding.

3.  During the addition of the switch to the stack, make sure you power the new switch OFF, connect the stack cable before applying power.

4.  When the new switch has come up and is seen by the stack, then use the "switch   priority " command.

[Kishore Chennupati · Accepted solution]

Hi,

I definetly agree with leo that a switch stack more than even 5 would be a pain. The CPU always spikes up and when you make changes the lag gives you a feeling that you killed the stack. Also you have to be very careful whilst upgrading IOS's and adding new swtiches to the stack as any small error, you could potentially bring the whole stack down .

However, there is enough documentation around to help you out to understand them better. Stacks are good commercially as well. I mean, if a site is no longer requried you can dismantle the stack and you the switches elsewhere in the network henceby reducing the CapEx. Imagine, if you went for a 4507 or something and its no longer needed because the site is shutdown.You have to wait for a decent size office again to reuse the chassis or need to have a fault around with other 4507 so that you can re-use the blades.

if you have any questions regarding the stacks, please continue to post them here and we will try to assist you.

HTH,

Regards

Kishore

[ciscobigcat]

Thank you so much for the help.

Now, since you are both agreeing, I can present it to the customer and tell them about this "best practice" of not having more than 5 or 6 switches on a stack.

But here is the deal, the stack currently has 7 switches and the last time I touched it, like 2 weeks ago, I was configuring some ports and I was using the range command and I did not notice any noticeable lag.

But I do follow good advise that come from the big cats here but the question now becomes: what do I do with the new switch? I have a stack of 7, and another new switch, so what do I do? The new switch is because they are running short on ports.

My opinion is if there is a limit of 9 and I will be at 8, then I am good, but at the same time I do understand best practices. But what will be the best thing to do here? and being very unintrusive and not really re-designing the network, or do I really need to?

Currently the network works, there are no complaints about speed, or anything like that. Now, if they are getting the best out of it, I dont know. I would need tools for this to measure/capture data and see how the overall stack is behaving. They have 3 VLANs, servers, printers and the other one is for workstatoins and voice.

Today I had really set aside to configure the new switch and add it to the stack but I can wait to see your input and what we can do.

thank you again

[Leo Laohoo · Accepted solution]

Ok.  Thanks for the ratings.  Here are some of my thoughts ...

Firstly, you have the option of staying put or breaking your stack into two.  First, I'd like to talk about breaking them into two.

Let me see, you say you're going to add two more switches to your stack of six and brings a total of 8.  You have the option of cutting the entire stack by half (or a stack of 4).  Then you "balance" them in the future.  Say if you need to add two more then you add one stack member to each stack, balance.

Your next issue is your uplink.  Normally in a stack of more than two, I make it a habit, particularly if you don't have the luxury of 10Gb uplinks, of making multiple uplinks or EtherChannel.  This is for two main reason:  oversubscription and redundancy.  Redundancy is self-explainatory.  Oversubscription, however, is something else.  Normally what I preach is for every 48-port switch there's at least one 1Gb link to the distro or core.  Sometimes is more expensive to follow my own recommendation because the cost of laying fibre down ain't something to snort about.  But if you have enough fibre, for a stack of 4, I'd think about an EtherChannel of a minimum of 3 uplinks.  This will guarantee you have very adequate uplinks in case the master should fail PLUS you have an added bonus of throughput.

Right, now lets talk about staying put.

But here is the deal, the stack currently has 7 switches and the last time I touched it, like 2 weeks ago, I was configuring some ports and I was using the range command and I did not notice any noticeable lag.

Darn good argument with me.  If you firmly believe that you don't see any lags then go for it.  However, table the risk to management so you get them prepared should the need to break the stack into two.

My opinion is if there is a limit of 9 and I will be at 8, then I am good, but at the same time I do understand best practices.

Errr ... I've never heard of the best practices that specifies the best quantity of stack members in a stack.  The so-called "best practices" are from people who have experiences in the wild and putting those experiences and pitfalls in accomodating forums like this.

As for the term "big cats", I'm not one.  I'm here on a quest for learning and collaborating. 

[Kishore Chennupati · Accepted solution]

Hi,

Since you already got a stack and just need to add another one. Maybe you can just add it for now and continue rather than mucking around with it since the stack is in production already. Leave the stack as is and just follow cisco documentation of  "how to add a new switch to a stack". Just keep monitoring this using some NMS tools.

And, in future if you have another reuirement for such a setup, you can explain to the business of creating and managing stacks etc and follow some strategy of having 2 stacks or single stack.

Thanks for the ratings.:-)

HTH,

Regards,

Kishore

[ciscobigcat]

Very very helpful guys. I have observations from different angles and this is always better.

The new switch, the 8th one, was added to the stack and after some minor obstacles, it is now up and running. Again, I have not noticed any lag and all seems pretty smooth.

While adding this new 8th switch to the stack and running into the obstacles that I ran into, I called TAC to get me out of jail because the customer asked for this to be done right in the middle of the day. This made the whole addition process very delicate and when I ran into the obstacle, I called those guys right away.

While working with TAC, the tech told me that she had not heard of any expected degradation of performance once you get close to the limit of 9 switches on a stack. She mentioned that this is not a problem and that they see this every single day and added that the calls they get is just for other issues rather than for a limitation or "best practices".

I don't know where I got that from but I think it was from a thread here. So, with your input and cisco's confirmation I do not believe that any longer. If customer needs more ports, I will put that stack to its limit!

I also do agree that breaking the stack in 2 would have been a better route and maybe more scalable, but since this is in production I will just leave it like that.

Thank you again for all the input. This cisco forum is really a key place to learn stuff. I can really get all my configs from here but on the same token I know how to balance it with TAC as they will always be there to confirm anything I might learn here and to fix anything that is broken

ciscobigcat

[Joseph W. Doherty]

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

One advantage of using HSRP with a stack, the virtual MAC doesn't change when the stack master fails, although there is also a command to "pin" the original stack master's MAC.