Dell PowerConnect PC7024 Quick reference guide

Stacking Dell PowerConnect
7000 Series Switches
A Dell Technical White Paper
www.dell.com •support.dell.com

Stacking Dell PowerConnect 7000 Series Switches
Page ii
THIS WHITE PAPER IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICAL
ERRORS AND TECHNICAL INACCURACIES. THE CONTENT IS PROVIDED AS IS, WITHOUT EXPRESS OR
IMPLIED WARRANTIES OF ANY KIND.
© 2011 Dell Inc. All rights reserved. Reproduction of this material in any manner whatsoever without
the express written permission of Dell Inc. is strictly forbidden. For more information, contact Dell.
Dell, the DELL logo, and the DELL badge, PowerConnect, and OpenManage are trademarks of Dell Inc.
Other trademarks and trade names may be used in this document to refer to either the entities
claiming the marks and names or their products. Dell Inc. disclaims any proprietary interest in
trademarks and trade names other than its own.
PC7024, PC7048, PC7024P, PC7048P, PC7024F, PC7048R, PC7048R-RA, PCM6348
July 2011

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Contents
Introduction ................................................................................................................ 2
Applicability .............................................................................................................2
Stacking and Management ............................................................................................2
Stacking and Performance ............................................................................................3
Stacking and Redundancy .............................................................................................3
Mixing M6348 and PC7000 Series Switches in a Stack ............................................................5
Power-Up Sequencing Considerations...............................................................................5
Initial Installation and Power-up of a Stack ..........................................................................7
Selecting the Master Unit................................................................................................8
Selecting the Standby Unit ..............................................................................................8
Updating the Firmware on a Stack .....................................................................................9
Automatic Update ......................................................................................................9
Manual Update ........................................................................................................ 10
Creating a Separate VLAN for File Downloads................................................................... 11
Adding a Stack Member with Minimal Interruption................................................................ 16
Removing a Stack Member with Minimal Interruption ............................................................ 17
Merging Two Operational Stacks...................................................................................... 18
Synchronizing the Running Configuration between the Master and Standby Units .......................... 18
Master Failover .......................................................................................................... 18
Effect of Master Failover on PoE Devices......................................................................... 18
Stack Member Failover ................................................................................................. 19
Failover Scenarios....................................................................................................... 19
Scenario 1.............................................................................................................. 19
Scenario 2.............................................................................................................. 20
Scenario 3.............................................................................................................. 21
Nonstop Forwarding..................................................................................................... 22
Initiating a Warm Failover of the Manager Unit................................................................. 23
Nonstop Forwarding Scenario....................................................................................... 23
NSF Scenario Configuration via CLI ............................................................................. 25
NSF Example 1...................................................................................................... 29
NSF Example 2:..................................................................................................... 29
NSF Re-convergence Timing........................................................................................... 30
Medium Configuration .................................................................................................. 30
Small Configuration ..................................................................................................... 31
Stacking CLI Commands ................................................................................................ 31
Stacking Web Interface................................................................................................. 32
Summary .................................................................................................................. 32

Stacking Dell PowerConnect 7000 Series Switches
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Introduction
This white paper explains the purpose and operation of the stacking feature in the Dell™
PowerConnect™ 7000 Series Gigabit Ethernet switches. The PowerConnect 7000 series is Dell’s most
advanced switching product line, offering advanced switching capabilities including high-density, high-
performance stacking, and 10 Gigabit Ethernet capabilities that scale from the small business to the
Enterprise Edge. Stacking allows multiple switching units to be combined together to act as a single,
high-performance, highly resilient switching unit with a single management interface. Units can be
added to increase throughput as needed. With each stack unit supporting up to 184 Gbps in switch
capacity, the customer can have almost 2 terabits of capacity in a single stack.
In addition, stacks can be composed of an interchangeable mix of PowerConnect 7000 Series switches
and PowerConnect M6348 switches, enabling administrators to continue to leverage the full utility of
previous-generation switches while transitioning to the latest-generation equipment. See “Mixing
M6348 and PC7000 Series Switches in a Stack” on page 5.
Applicability
This paper applies to the PowerConnect 7000 series switches, which includes the PC7024, PC7048,
PC7024P, PC7048P, PC7024F, PC7048R, and PC7048R-RA Dell model numbers. Each PowerConnect
switch has two bays that can be customized to support a stacking or an uplink configuration. Each bay
can contain a CX-4, SFP+, or a 10GBase-T module. Stacking is supported only on CX-4 modules in either
or both bays. CX-4 stacking modules can be configured in 16 Gbps stacking mode or 10 Gbps Ethernet
uplink mode. CX-4 stacking modules default to stacking mode, where the maximum cable length is
3 meters. When the stacking modules are configured to operate in Ethernet mode, the maximum cable
length is 12 meters.
The PCM6348 has two 10 Gbps SFP+ ports, and two separate 10 Gbps Ethernet ports that support CX-4
modules for stacking.
The following table summarizes the features of the PowerConnect 7000 series and PCM6348 switches.
Part Number
Gigabit Ethernet
Ports (RJ-45)
Gigabit Ethernet
Ports (SFP)
Modules
(Stacking, SFP+,
10GBASE-T)
Other
Features
PCM6348
161
2
4
PC7024
24
42
2
PC7024P
24
42
2
PoE4
PC7024F 4 24 2
PC7048 48 4
3
2
PC7048P 48 4
3
2 PoE
4
PC7048R/ PC7048R-RA 48 4
3
2 Top-of-Rack
5
1. The PCM6348 also has 32 internal ports that connect to server blades in a chassis.
2. Shared with ports 21–24.
3. Shared with ports 45–48.
4. Each copper port can provide up to 30W of power to an external powered device.
5. The difference between the PC7048R and PC7048R-RA switches is the airflow direction.
Stacking and Management
An important advantage of stacking is that it provides a consolidated interface for management of
multiple switches when linked together. When a stack is already deployed in the network, operators
can add units to the stack as their port requirements increase, with minimal administrative overhead

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required for reconfiguration. Additional stack members can immediately utilize existing configuration
information such as routing and switching configurations, VLANs, ACLs, port profiles, and security
certificates.
Stacking and Performance
For situations where there is a need to pass traffic between switches and the aggregate bandwidth
required between PowerConnect 7000 Series switches does not exceed 64 Gbps (2 ports, 16 Gbps Tx
and Rx each), a stacking configuration offers an attractive alternative to Link Aggregation Groups
(LAGs). Stacking configuration is generally transparent to the operator and does not require
configuration beyond cabling. In addition, failover times are generally faster in a stack configuration
than in spanning tree or link aggregation group configurations. Note that other PowerConnect Series
switches may have different supported bandwidths for stacking.
Stacking and Redundancy
By connecting a cable from the last switch in a stack back to the first switch, the operator ensures that
a stack has the protection of redundant paths for control and data traffic, including support for LAGs
configured across multiple switches. This means that any single point of failure (a switch or a stack
cable failure) will not affect the overall operation of the remaining stack elements.
#Figure 1 shows two stacking configurations with a single stacking module on each switch. In the
recommended configuration, a stacking cable connects each switch to the next, and the top switch is
connected to the bottom switch to form a complete ring.
Figure 1. Stack Configured in a Ring
Recommended Not recommended
Module
ASwitch
1
2
3
4
5
Switch
1
2
3
4
5
Module
A
aCables connected in a complete ring. r Cables not connected in a complete ring.

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#Figure 2 shows a recommended stacking configuration with dual stacking modules on each switch. Each
switch connects to another with 128 Gbps of total bandwidth (4 ports @ 16 Gbps Tx and Rx each). Note
that in the recommended configuration, the dual stacking cables from each module both connect to
the same switch. In the not-recommended configuration, the dual stacking cables on switch 2, module
B and switch 3, module B connect to two different switches.
NOTE:To ensure full bandwidth when using redundant links between two switches, be sure not to split
the links across modules. Keep redundant links isolated to a single module on each end as shown in the
recommended configuration in #Figure 2.
Figure 2. Dual Stacking Modules Configured in a Ring
Recommended Not recommended
Module
AModule BSwitch
1
2
3
4
5
Switch
1
2
3
4
5
Module
AModule B
a Cables connected in a ring.
a Dual stacking cables connect both ports
r Cables not connected in a complete ring.
r Dual stacking cables connect ports on a module to
two different switches. on a module to the same switch.

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Mixing M6348 and PC7000 Series Switches in a Stack
PC7000 series and M6348 can be used interchangeably in a stack of up to 12 units. As with PC7000-
series only stacks, all switches in a mixed stack must have the same firmware version. Starting with the
4.1.0.6 software release, a single image supports both switches. No additional configuration is
required.
Either the PC7000 series switch or the M6348 switch can be the master.
NOTE: A stack that includes an M6348 switch (as the master or a member) can operate only in Normal
mode—not in Simple mode.
#Figure 1 shows a stack with a mix of PC7000 series and M6348 switches.
Figure 3. Mixed Switches in a Stack
PC7048
PC7048P
PCM6348
PCM6348
PC7024 1
2
3
4
5
Power-Up Sequencing Considerations
One unit in the stack acts as the master unit. The master manages all the units in the stack. A second
switch is elected as the standby unit, which becomes the master if the master unit is unavailable.
The administrator can manually configure which unit is elected as the standby, or the system can
select the standby automatically. To configure it manually, the administrator can use the Stacking
Management > Unit Configuration page in the web interface or the standby command in the CLI.
NOTE: The terms “master” and “manager/management unit” are used interchangeably throughout this
document.
The selection of the manager and standby units is important in situations where the administrator
wishes to utilize the serial port for management, perhaps as a backup console. Management of the
stack via the out-of-band service port or the in-band ports is transparent in a stack.
In a stacking configuration, the power-up sequence determines the manager and standby units. The
switch that the operator selects as the manager should be powered up first and should be allowed to
fully come up before the other stack units are powered up. The standby switch should always be
directly connected to the manager. Once the manager and standby have powered up fully, other

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members of the stack can be powered on sequentially by powering up the switch adjacent to the last
switch powered on.
A stack of units is managed and acts as a single entity when the units are connected together and are
operational. If a unit cannot detect a stacking partner, the unit automatically operates as a stack of 1
with itself as the master. If a stacking partner is detected, the switch always operates in stacking
mode.
When units are operating together as a stack, the following activities occur:
•All units are checked for firmware version consistency on startup. By default, units
with older versions of firmware are automatically upgraded with the operational
firmware version on the master switch as they join the stack. If a unit has a newer
software version than the master, it is not downgraded to the master’s version by
default; however, the administrator can use the following command to enable this
functionality:
console#boot auto-copy-sw allow-downgrade
Before adding a member that has newer version of software to a stack, the
administrator should enable the automatic downgrade feature on the master switch.
•Switch management and protocols such as OSPF are active only on the master, but
apply to all members of the stack. Unless administratively disabled, the Nonstop
Forwarding (NSF) feature periodically checkpoints the running configuration and the
application state between the master and standby switches during normal stacking
operation. If the master fails, the standby switch takes over operation of the stack.
•Data forwarding is active on all units in the stack, including the master. Data
forwarding continues to operate should the master become unavailable.

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Initial Installation and Power-up of a Stack
Follow these instructions to create a stack:
NOTE: Install units in a rack whenever possible to prevent the units and cables from being disturbed.
1. Install all stacking cables. Fully connect all cables, including the redundant stack link.
CAUTION! We highly recommend that a redundant link be installed to provide stack resiliency.
2. Select a unit to be the manager unit. Power this unit up first.
3. Monitor the console port on the manager unit. The unit will automatically become a manager
unit. If not, renumber the unit as desired. The Stack Management > Unit Configuration page in
the web interface or the switch renumber command in the CLI can be used to change the
unit number.
4. If desired, pre-configure other units to be added to the stack. This is not usually necessary.
5. Power on a second unit, making sure it is adjacent (directly connected) to the manager unit.
This ensures the second unit comes up as a member of the stack, not as the manager of a
separate stack.
6. Monitor the manager unit to see that the second unit joins the stack. Use the show switch
command to determine when the unit joins the stack. It will be assigned a unit number (unit
#2, if it has the default configuration). The output of the show switch command should
indicate the unit status as “OK” if the member has been successfully added to the stack. If the
unit status is "code mismatch" and stack auto-upgrade is disabled, then use the copy image
unit command to update the code on the unit. If the unit status is "Cfg Mismatch", then use
the no member <unit-number> command to resolve the issue.
7. If desired, renumber this stack unit using the switch renumber command.
8. Repeat steps #4 through #6 to add additional members to the stack. Always power on a unit
directly connected to the units already in the stack.
9. Enter the show switch stack-port counters command on the manager and see if there
are any stack port errors being reported. Replace the stacking cables/modules if stack errors
are being reported and begin the power-up sequences again for the affected units and any
downstream units.

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Selecting the Master Unit
A stack manager is elected or re-elected based on the following considerations, in order:
•Whether the switch that was previously the stack manager.
•Whether the switch has the higher MAC address.
When a switch is added to the stack, one of the following scenarios takes place:
•If the switch was previously designated as the stack master but another master unit is
already active, then the switch changes its configuration to be a slave unit.
•If the switch was not designated as the stack master and there is another stack master
in the system, then the switch changes its configuration to be a slave unit.
•If the switch is enabled as the stack master or there is no other stack master, then the
switch becomes stack master.
•If the switch is not enabled as the stack master, the unit remains a slave unit.
The administrator can manually set the unit number for the switch using the Stack Management > Unit
Configuration page in the web interface, or the switch renumber command in the CLI. To avoid
unit-number conflicts, one of the following scenarios takes place when a new member is added to the
stack:
•If the switch has a unit number that is already in use, then the unit that is added to the
stack changes its configured unit number to the lowest unassigned unit number.
•If the added switch does not have an assigned unit number, then the switch sets its
configured unit number to the lowest unassigned unit number.
•If the unit number is configured and there are no other devices using the unit number,
then the switch starts using the configured unit number.
•If the switch detects that the stack already has the maximum number of units, making
it unable to assign a unit number, then the switch sets its unit number to “unassigned”
and does not participate in the stack.
If a new switch is added to a stack of switches that are already powered and running and already have
an elected master unit, the newly added switch becomes a stack member rather than the master. On
the master unit, if there is no saved configuration for the newly added unit, it applies the default
configuration. If there is a saved configuration on the master for the newly added unit, it would apply
the saved configuration to the new unit. If the entire stack is powered OFF and ON again, the unit that
was the master before the reboot will remain the master unit after the stack resumes operation.
Selecting the Standby Unit
When the stack is formed, one of the units is automatically selected as the standby unit for the stack.
The standby unit takes over as manager if the current manager fails. Alternatively, the administrator
can specify the standby unit.
To configure the standby unit using the CLI, use the standby command in Stack Configuration Mode.

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To configure the standby unit via the Web interface, view the Stacking > Unit Configuration page and
select Standby for the Unit Type.
Updating the Firmware on a Stack
Automatic Update
By default, firmware synchronization is performed automatically when a unit is powered up on a stack.
Because firmware synchronization makes no attempt to check for the latest version of firmware, the
following procedure is recommended for bringing all members of a stack onto the same version of
code.
NOTE: Schedule some downtime as this process will reset the entire stack and affect all stack users.
1. Use the following commands to enable firmware synchronization, if needed, and write the
running configuration to the saved configuration:
console#boot auto-copy-sw
console#copy nvram:config copy system:running-config nvram:startup-
config
2. Load the more recent firmware image onto the stack master as the backup image.
3. Set the stack master to reboot from the new image:
console#boot system backup

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4. Reload the stack command. This resets the entire stack. The switches stop forwarding during
the reset.
5. When the stack has reloaded, check the running firmware version using the show version
command. Check that all stack members have joined the stack using the show stack
command. Members that failed to update may be recovered using the manual update
procedure described in the following section.
6. If successful, disable firmware synchronization on the stack and save the running configuration.
Manual Update
The administrator can perform firmware updates on the stack by using the CLI or the Web interface.
From the CLI, use the copy ftp command, which uses the FTP protocol for file transfer. To update
the firmware by using the Web interface, use the options available on the System > File Management
> File Download from Server page.
NOTE: When stacked, the PC7000 switches require that the same version of firmware be installed on
every switch member.
When connected in stack, the copy ftp or copy tftp commands will distribute the downloaded
image to all the connected units of the stack.
In the following output, the image with a file name of image.stk is downloaded from the FTP server
with an IP address of 10.27.64.141.
console#copy ftp ftp://10.27.64.141/image.stk image user admin password
test1234

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Mode........................................... FTP
FTP Server IP.................................. 10.27.64.141
FTP Path.......................................
FTP Filename................................... PC7000_4.0.0.6.stk
Data Type...................................... Code
Destination Filename........................... image
Creating a Separate VLAN for File Downloads
When updating the firmware, it is helpful to keep the in-band management port in a different VLAN
and configure the port VLAN ID (PVID) appropriately to avoid the possibility of network congestion or
flooding issues impacting the file download.
The CLI commands in the following example show how to configure port gi1/0/17 as an in-band
management port for firmware downloads or management access.
console#configure
console (config)#vlan database
console (vlan)#vlan 1000
console (vlan)#exit
console (config)#interface vlan 1000
console (config-if-vlan1000)#ip address 192.168.21.11 255.255.255.0
console (config-if-vlan1000)#exit
console (Config)#interface ethernet gi1/0/17
console (config-if-gi1/0/7)#switchport mode general
console (config-if-gi1/0/7)#switchport general pvid 1000
console (config-if-gi1/0/7)#switchport general allowed vlan add 1000
console (config-if-gi1/0/7)#switchport general allowed vlan remove 1
console (config-if-gi1/0/7)#exit
console (config-macal)#management access-list MGMT_VLAN
console (config-macal)#permit ip-source 192.168.21.0 mask /24 vlan 1000
console (config-macal)#service ssh
console (config-macal)#exit
console (config)#management access-class MGMT_VLAN
The switch now segregates traffic arriving on port gi1/0/17 onto VLAN 1000. All untagged packets that
enter the port are tagged with a VLAN ID of 1000. Additionally, only hosts with an IP address in the
192.168.21.XXX subnet are allowed access to the switch using SSH. The 192.168.XXX.XXX address block
is a private address space per RFC 1918. As an added security measure, network administrators can
configure their organization’s edge routers to drop ingress and egress traffic destined to this address
block.

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To perform the same configuration by using the Web interface, use the following steps:
1. From the Switching > VLAN > VLAN Membership page, click Add.
2. From the Add VLAN page, enter 1000 in the VLAN ID field and click Apply.
3. From the Ports menu on the Switching > VLAN > Port Settings page, select port Gi1/0/17.
4. Configure port gi1/0/17 in General mode with a PVID of 1000 and click Apply Changes.

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5. From the Show VLAN menu on the Switching > VLAN > VLAN Membership page, select 1000.
6. Click the Static box for port 17 so that the letter U(untagged) appears in the box.
7. Click Apply.
8. Navigate to the Routing > IP > IP Interface Configuration page.

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9. In the Interface field, select VLAN 1000. In the Routing Mode field, select Enable. In the IP
Address Configuration Method field, select Manual. In the IP Address field, enter
192.168.21.11. In the Subnet Mask field, enter 255.255.255.0. Click Apply.
10.Navigate to the System > Management Security > Access Profile page. Choose the Add Profile
tab. Enter MGMT_VLAN in the Access Profile Name field. Select the Interface check box and
the VLAN radio button. Choose 1000 in the VLAN drop down. Enable the Source IP Address
check box and enter 192.168.21.0 in the Source Ip Address field. Enter 255.255.255.0 in the
Network Mask field. Ensure that the Action field is set to Permit and set the Rule Priority
field to 1.

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11.Click Apply.
12.Navigate to the System > Management Security > Access Profile page. Choose the Access
Profile tab. Enable the Set Active Access Profile check box in the MGMT_VLAN Access Profile
and click Apply.

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Adding a Stack Member with Minimal Interruption
When adding a new member to a stack, make sure that only the stack cables and no host-facing
network cables are connected before powering up the new unit. Make sure the end-user links are not
connected to any ports on the unit being added and the new member is powered off. This is important
because if STP is enabled and any links are UP, then Spanning Tree Protocol (STP) re-convergence will
take place as soon as the link is detected.
After the stack cables on the new member are connected to the stack, connect the switch power. Do
not connect another switch to the stack until the existing members are powered up. Also, do not
connect two functional, powered-up stacks together. If two functional, powered-up stacks are
connected together or connect a powered-up new member to the stack, then master re-election takes
place, which causes the stack that no longer has a master to reboot. See “Merging Two Operational
Stacks” for more details.
An “unassigned unit” is a switch that is preconfigured to be a member of a stack, but has not been
physically connected to the stack. If there are any unassigned units already configured on the stack,
remove them prior to adding a new unit to stack. This is important because when there is any
preconfigured unit and the master holds some configuration for that unit, as soon as the new unit is
detected, the configuration is applied, which might trigger the re-convergence or startup of many
other protocols. However, it is possible to intentionally pre-configure a unit. The
preconfigured/unassigned units can be viewed by using the show switch CLI command shown below.
The following example shows how to view the units in the stack and remove an unassigned unit:
console#show switch
Management Standby Preconfig Plugged-in Switch Code
SW Status Status Model ID Model ID Status Version
--- ---------- --------- ------------- ------------- ------------- ----------
1 Mgmt Sw PCT7048P PCT7028P OK 4.0.0.6
2 Unassigned PCT7028P Not Present 0.0.0.0
console#configure
console(config)#stack
console(config-stack)#no member 2
console(config-stack)#exit
console(config)#exit

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Removing a Stack Member with Minimal Interruption
NOTE: This migration process can be disruptive, so schedule some outage time. To minimize any
disruption, plan on having one or more test scenarios prepared in order to verify that the migrated
ports are operating properly.
1. Migrate end-user ports to appropriately configured ports on a different stack member. Verify
that the migrated end-user services are operational. If an end user is not operational, it is
possible to recover quickly by connecting the end user back to the original port.
2. Migrate any trunk ports to an appropriately configured port on a different stack member. Verify
the operation of the new trunk port. This may require several steps:
a. Remove spanning tree configuration from the ports on the stack member to be
removed.
b. Remove LAG configuration from the ports on the stack member to be removed.
c. Reroute any statically routed traffic going through the stack member.
3. Remove the member from the stack, re-cable around the member, checking that the cabling is
positively connected and does not show stacking errors. Power off the removed member.
To remove a switch from the stack by using the Web interface, navigate to the System > Stack
Management > Unit Configuration page. Select the switch to remove from the Switch ID drop down,
and then select the Remove Switch option. Then, click Apply.

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Merging Two Operational Stacks
The recommended procedure for merging two operational stacks is as follows:
Caution! This procedure is disruptive and requires a network outage.
1. Always power off all units in one stack before connecting to another stack.
2. Add the units as a group by unplugging one stacking cable in the operational stack and
physically connecting all unpowered units.
3. Completely cable the stacking connections, making sure the redundant link is also in place.
Two operational stacks can also be merged by reconnecting stack cables without powering down units
in either stack. Connecting a powered-up standalone unit to an existing stack leads to same behavior as
when merging two operational stacks. In such cases, manager election is performed and the manager
unit with the higher MAC address is chosen as manager. The stack that no longer has a stack manager
resets itself and all of its member units. After the reset, all the stack members in the reset stack join
the stack that has the manager to form a single stack. The stack that has the manager remains
functional through the merge process.
Synchronizing the Running Configuration between the
Master and Standby Units
The master unit copies its running configuration to the standby unit whenever the configuration
changes (subject to some minimal time delays introduced in the copy mechanism to increase the
efficiency of the transfer process). This enables the standby unit to take over the stack operation with
minimal interruption if the master unit becomes unavailable.
The running-config synchronization also occurs:
•When the administrator saves the running configuration to the startup configuration on
the master unit.
•When the standby unit changes.
Master Failover
If the current master unit fails, the standby unit becomes the master unit. If no switch is preconfigured
as the standby unit, the firmware automatically selects a standby unit from the existing stack units.
When the failed master resumes normal operation, it joins the stack as a member (not a master) if the
new master unit has already been elected.
The stack supports nonstop forwarding and graceful restart during a master failover. See “Nonstop
Forwarding” on page 22.
Effect of Master Failover on PoE Devices
Stack members that provide power-over-Ethernet (PoE) to connected devices continue to provide
power in the event of a master failover. The PoE application uses a separate controller on each unit,
and these controllers are not initialized upon a warm restart.