Force10 MXL Switch: Stacking

Overview

There are two typical scenarios for stacking MXL’s – within the chassis and across the chassis. In both cases it’s recommended to use ring topology. Daisy chaining is also supported, but not desirable because of the lack of redundancy.

In this post I will be describing the more common case, which is intra-stacking. For inter-stacking configuration you can refer to Dell or Force10 documentation.

Cabling

In my case I have four MXL switches in bays A1, B1, B2, A2. Cabling is simple, you basically daisy chain all switches and then plug the last switch to the first one.

Stack roles and unit numbers

When stack is built each switch is assigned an ID starting 0 and a role in the stack. There are three roles: Master, Standby and Member:

• Master – is the switch you’ll use for all configuration. If you currently have IPs assigned to all your MXL switches, all of them except for one will be reset and only the Master will be accessible via SSH.
• Standby – is the switch which takes over if Master switch fails. Master switch IP address is transferred to Standby in a failover scenario and stack continues to be managed via the same IP.
• Member switch provides port capacity and doesn’t play any additional roles in the stack.

When you plug cables in, assign stack ports and restart the switches, they will go through election process and automatically pick up roles, as well as IDs. There’s an algorithm that assigns stack IDs and roles, which switches follow. But this algorithm has nothing to do with interconnect bay IDs in the chassis or order in which you cable the switches. You end up with pretty much random numbering.

If order matters, then you’ll have to reboot switches one by one in a particular order to have the desired IDs assigned. In that case IDs are assigned sequentially in a controlled fashion.

Stack configuration

If you don’t have any additional 40GbE modules in slots 0 and 1, then you’ll end up with two QSFP+ ports in a built-in module – ports 33 and 37 (refer to my Force10 MXL Switch: Port Numbering post for port numbering details). All you need to do is to designate them as stack ports on all switches, save config and reboot.

# stack-unit 0 stack-group 0
# stack-unit 0 stack-group 1
# copy run start
# reload

By default each switch is unit 0 in its own stack and stack-group is basically just a 40GbE stack port. You can have maximum of six such ports numbered from 0 to 5. To check that stack ports have been enabled run:

# do show system stack-unit 0 stack-group configured

It could be that your 40GbE ports are in quad 10GbE mode and are not shown. You’ll need to convert them back to 40GbE mode to proceed. To show the list of available ports type in the command below. Switch shows empty expansion slots as stack ports as well (port 0/41 and 0/45), which is a bit confusing.

# show system stack-unit 0 stack-group

After a reboot, switches will join the stack and get a role and an id. This process is automatic by default. To see if stack ports have come up after a reboot type:

# show system stack-port status

Conclusion

In my example I let switches to go through election process and select roles and IDs on their own. If you want to control the assignment process refer to Dell and Force10 documentation for instructions.

Now you may wonder if unit IDs are assigned automatically, how do you know which stack unit corresponds to which chassis bay ID. The hint for that is to show system inventory and map them by the Service Tag ID which is also shown in the Chassis Management Controller:

# show system brief
# show inventory

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Tags: 10GbE, 40GbE, Bay, cabling, Daisy Chain, dell, Election, Force10, ID, Master, Member, MXL, Quad, Ring, role, stack, Stack-Group, Stack-Unit, standby, topology, Unit