3750X Switch Stack a few Queries

[avilt]

Conside a stack of two 3750X-24-E switches with IP service image.

How can I view/monitor the backplane usage? (Traffic between the subnets/vlans)

With the stack in palce, is it mandatory to implement HSRP to provide layer 3 routing redundency? Is it not possible to provide the routing redundency with the stack feature itself since each stack member maintains the complete configurations?

[Thotsaphon Lueangwattanaphong · Accepted solution]

Hello,

    It's hard to monitor the backplane usage as you want. You might see average traffic in/out of VLAN interface instead. It's not possible to do HSRP in stack switches. It acks as just one switch. Stack master will take care of things. So in case you lost master or member you will be fine with routing.

HTH,

Toshi

[avilt]

Catalyst 3750 Switch Software Configuration Guide, Chapter 42 is about HSRP.

So when do we need HSRP on a 3750 switch? I am familiar with HSRP on router side. Could you give me the scenarios where HSRP is necessary @ 3750-switch level?

[Joseph W. Doherty · Accepted solution]

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.

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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

When using a 3750 stack, the stack itself provides redundancy, so often there is no need to use HSRP.  However, you might still want to use it if there's more than one gateway device.  Even when there's only a 3750 stack for the gateway device you might still want to enable HSRP so that gateway MAC doesn't change when the stack master fails (although that can also be addressed by changing the default regarding gateway MAC usage) or if you envision ever moving gateway from one device (including a stack) to another gateway device.

[Ven Taylor · Accepted solution]

Put simply, the stack makes the two switches act as a single switch.

If you're looking for redundancy via HSRP (or VRRP) I'd recommend breaking the stack and utilizing each 3750 as a single L3 switch.

If that's not a concern, then stick with the stack and make sure each switch in the stack has an uplink connection.

Ven

[avilt]

Thank You for the explanation.

In the stack, is backplane = stack cables?

[Ven Taylor · Accepted solution]

Yes and no.

Each switch has its own backplane, but the stack cables create a 32Gbps interconnect.

In my weird mind, my way of seeing it is that each switch uses backplane for port-to-port / asic-to-asic communications, but inter switch communications uses the stack cable.  It's obviously faster than daisy-chaining switches. It's also a lot easier for management.  You end up with Gig1/0/1 - 48, then Gig2/01 - 48.

Most importantly, architect the switches prior to installation to make sure the top switch is switch 1, followed by switch 2 below it, and so on.  You can do this by provisioning each switch, followed by numbering and prioritizing each.

The command to provision is switch 1 provision (switch type)

The command to re-number is switch 1 renumber 2 (or whatever numer)  followed by a reload.

The command to prioritize is switch 1 priority 15.

Lastly, I always do this:

Switch 1 - priority 15  - has uplink  

Switch 2 - priority 12

Switch 3 - priority 10

Switch 4 - priority 8

Switch 5 - priority 6   - has uplink

As you get more switches in the stack, you have to be clever with your stack cabling to ensure you don't isolate a switch if you have a failure.  Draw it on a white board and cover each switch one at a time, then find out if each switch has a route out.  Avoid those single points of failure!!!

Here's a link to a white paper Cisco put together about Stackwise technology.

It's short and very informative.

Ven

[Joseph W. Doherty · Accepted solution]

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

Ven Taylor wrote:
Yes and no.
Each switch has its own backplane, but the stack cables create a 32Gbps interconnect.

NB: E and X series have Stackwise+, which provides "64 Gbps" (and other enhancements).

[avilt]

Thank You for the detailed explanation. Currently I am using Nagios for monitoring switch (not stack) status using ping. If I have a stack how can I monior all the switches in the stack individually since the entire stack is assigned one single IP address?

[Ven Taylor]

You can still monitor it like any other switch.  It just shows up with more power supplies and more interfaces.

Ven

[avilt]

Since the entire stack is assigned a single IP address and nagios is monitoring the stack IP, how can nagios detect/differentiate master or member switch failure?