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T
he Cisco IOS and CatOS operating systems run on Cisco
network switches and provide Cisco EtherChannel,
Fast EtherChannel (FEC), and Gigabit EtherChannel
(GEC) technologies, which enable network administra-
tors to group ports on Cisco switches together to increase
available throughput. Dell PowerConnect switches offer
a similar technology known as link aggregation groups
(LAGs), which are designed to increase the overall band-
width between two Dell switches by aggregating multiple
ports to act as a single, logical connection between the
switches. Dell PowerConnect 5316M switches implement
IEEE 802.3ad–based link aggregation, which is interoper-
able with Cisco EtherChannel technology.
Link aggregation on Dell PowerConnect switches can
be configured as either dynamic or static. The dynamic
configuration uses the IEEE 802.3ad standard, which is
also known as Link Aggregation Control Protocol (LACP).
LACP enables a Gigabit Ethernet switch to confirm that
the external switch is also configured for link aggrega-
tion. Static configuration is used when connecting the
Dell PowerConnect 5316M Gigabit Ethernet switch to an
external Gigabit Ethernet switch that does not support
LACP. In a static configuration, a cabling or configura-
tion mistake involving the PowerConnect 5316M or the
external switch could go undetected and thus could cause
undesirable network behavior. Both static and dynamic
LAGs (via LACP) can detect physical link failures within
the LAG and continue forwarding traffic through the other
connected links within that same LAG. LACP can also
detect switch or port failures that do not result in the
loss of a link, helping provide a more resilient LAG. Best
practices suggest using dynamic link aggregation instead
of static link aggregation.
The examples presented in this article use the command-
line interface (CLI) of the Dell PowerConnect 5316M to con-
figure the switch.^2 These example configurations also can
be implemented via the Web-based graphical user interface
(GUI) of the PowerConnect 5316M.^3
BY BRUCE HOLMES
Link Aggregation Interoperability
of the Dell PowerConnect 5316M Switch and Cisco Switches
This article explains how to configure the Dell
PowerConnect
5316M Gigabit Ethernet
switch, which resides within the Dell Modular Server Enclosure, to interoperate and
connect with Cisco IOS-based and CatOS-based switches by using industry-standard
link aggregation groups that adhere to the IEEE 802.3ad standard.
Related Categories: Blade servers Cisco Command line interface (CLI) Data networking Dell PowerConnect switches
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(^1) In dynamic configurations, this interoperability is possible only via LACP, not the proprietary Cisco Port Aggregation Protocol (PAgP). Link aggregation interoperability for all Dell PowerConnect products is tested at the University of New Hampshire InterOperability Lab. This lab tests products for the Bridge Functions Consortium, which includes leading vendors of switch and networking products. For more information, visit ftp://ftp.iol.unh.edu/pub/bfc/testsuites/la.io.test.suite.pdf. (^2) For more information about configuring LAGs via the CLI., see the “Port Channel Commands” section of the Dell PowerConnect 5316M CLI Reference Guidee at support.dell.com/support/edocs/ network/PC5316M/en/CLI/portchan.htm#1016308. (^3) For more information about configuring LAGs via the GUI, see the “Defining LAG Parameters” section of the Dell PowerConnect 5316M Ethernet Switch Module User’s Guidee at support.dell. com/support/edocs/network/PC5316M/en/UG/switch.htm#1125197.
104 DELL POWER SOLUTIONS Reprinted from Dell Power Solutions, February 2006. Copyright © 2006 Dell Inc. All rights reserved. February 2006
Link aggregation with Gigabit Ethernet switches
The following examples show minimal configurations necessary
to establish a LAG between a Cisco IOS-based Gigabit Ether-
net switch (Catalyst 3750), Cisco CatOS-based Ethernet switch
(Catalyst 6509), and the Dell PowerConnect 5316M Gigabit
Ethernet switch. These commands should work properly when
using the default configuration of each switch. Note: These com-
mands will erase any configuration data previously configured
and reboot the switch.
To set the Dell PowerConnect 5316M to the default configura-
tion, administrators should issue the following commands:
5316M# delete startup-config 5316M# reload
To set the Cisco IOS-based Catalyst 3750 switch to the default
configuration, administrators should issue the following com-
mands:
3 750# delete flash:/config.text 3750# reload
To set the Cisco CatOS-based Catalyst 6509 switch to the
default configuration, administrators should issue the following
commands:
Cat_6509 (enable) clear config all
Please see the “Configuration limitations” section in this article
for scenarios in which resetting the switches to factory defaults
would be impractical.
The Dell PowerConnect 5316M can support up to eight LAGs.
A port channel can have from zero to six of the external ports as
members. Internal ports cannot be members of a LAG. The examples
in this article use different numbers of ports in a LAG.
Best practices recommend that the ports to be aggregated on
both the Cisco and Dell switches be disconnected during configu-
ration. This will avoid any network loops being formed before the
LAG is set up.
Configuring the PowerConnect 5316M external ports for dynamic link aggregation
The following example shows the Dell PowerConnect 5316M CLI
commands for configuring the six external ports on the Gigabit
Ethernet switch for LACP:
5316M(config)# interface range ethernet g11- 5316M(config-if)# channel-group 1 mode auto
The first command sets the CLI mode to configure the six exter-
nal Gigabit Ethernet ports (referred to in the command as g11-16,
which represents Gigabit Ethernet ports 11 through 16). All 6 ports
do not have to be selected; a LAG can have from zero to six ports,
depending on the requirements of the network. The number of ports
in the LAG correlates to the amount of bandwidth and redundancy
achievable in the network—that is, the more ports, the more band-
width and redundancy. A LAG can even be configured without any
member ports. When ports are added to the LAG, they will be set
to the configuration of the LAG.
The second command aggregates the six ports into a LAG
(referred to in the command as channel-group), which will
use LACP (referred to in the command as mode auto). The
channel-group number, which is 1 in this example, has meaning
only within the switch and is used to differentiate up to eight
unique channel-groups. For each LAG created, administrators
must designate it with a number between one and eight for up
to eight groups. Only the external ports (11 through 16) can be
part of a LAG.
Configuring a Cisco IOS-based Gigabit Ethernet switch for dynamic link aggregation
The following example shows the Cisco IOS-based switch CLI com-
mands for configuring six ports for LACP:
3750(config)# interface range GigabitEthernet 1/0/1 - 6 3750(config-if)# channel-protocol lacp 3750(config-if)# channel-group 1 mode active
The first command sets the CLI mode to configure six Gigabit
Ethernet ports (referred to in the command as GigabitEthernet
1/0/1 – 6 , which represents Gigabit Ethernet ports 1 through 6).
The second command sets ports to use LACP as the LAG protocol
(and not PAgP). The third command aggregates the six ports into
a LAG (referred to in the command as channel-group), which
will use LACP (referred to in the command as mode active). The
channel-group number, which is 1 in this example, has mean-
ing only within the switch and is used to differentiate unique
channel-groups.
Configuring a Cisco CatOS-based Gigabit Ethernet switch for dynamic link aggregation
The following example shows the Cisco CatOS-based switch CLI
commands for configuring six ports for LACP:
Cat_6509(enable) set channelprotocol lacp 2 Cat_6509(enable) set port lacp-channel 2/1- mode active
106 DELL POWER SOLUTIONS Reprinted from Dell Power Solutions, February 2006. Copyright © 2006 Dell Inc. All rights reserved. February 2006
has meaning only within the switch and is used to differentiate up
to eight unique channel-groups. For each LAG created, administra-
tors must designate it with a number between one and eight for
up to eight groups. The internal ports that connect to the servers
do not support LAGs.
Configuring a Cisco IOS-based switch for static link aggregation
The following example shows the Cisco IOS CLI commands
for configuring three ports of the Cisco switch for static link
aggregation:
3 750(config)# interface range GigabitEthernet 1/0/9 - 11 3750(config-if)# channel-group 1 mode on
The first command sets the CLI mode to configure three Gigabit
Ethernet ports (1/0/9 through 1/0/11). The second command
aggregates the three ports into a static LAG. Static LAGs do not
use LACP and are defined in the Cisco CLI by setting the channel-
group mode to “on.” The channel-group number, which is 1 in
this example, has meaning only within the switch and is used to
differentiate channel-groups. The number of channel-groups sup-
ported by Cisco switches depends on the switch model.
Configuring a Cisco CatOS-based switch for static link aggregation
The Cisco CatOS CLI allows the configuration of static LAGs via
LACP or PAgP commands. The following example shows the Cisco
CatOS CLI LACP channelprotocol commands for configuring three
ports of the Cisco switch for static link aggregation:
Cat_6509(enable) set channelprotocol lacp 2 Cat_6509(enable) set port lacp-channel 2/9-11 mode on
The first command sets module 2 to use the LACP
commands to configure LAGs. Because a static LAG is
being defined, the setting for the channelprotocol com-
mand does not matter. The second command configures
the three Ethernet ports (2/9 through 2/11) into a static
LAG. Static LAGs do not use LACP and are defined in the
Cisco CLI by setting the lacp-channel mode to “on.”
The following example shows the Cisco CatOS CLI
PAgP channelprotocol commands for configuring three
ports of the Cisco switch for static link aggregation using
the PAgP command:
Cat_6509(enable) set channelprotocol pagp 2 Cat_6509(enable) set port channel 2/9- mode on
The first command sets module 2 to use the PaGP com-
mands to configure LAGs. As mentioned before, the setting for the
channelprotocol command does not matter because a static
LAG is being defined. The second command configures the three
Ethernet ports (2/9 through 2/11) into a static LAG. Static LAGs
do not use PAgP and are defined in the Cisco CLI by setting the
channel mode to “on.”
Confirming a successful static link aggregation connection
When LACP is not being used, only careful inspection of the Cisco
and PowerConnect 5316M configurations can confirm that a static
LAG has been established. Administrators can take the following
steps to help confirm the connection:
- Check that the cabling is connected to the correct ports on
both switches.
- Check that all the LAG ports have a link.
- Use the show running-config command to confirm that the
desired ports are in the LAG:
- (^) PowerConnect 5316M: 5316M# show running-config - (^) Catalyst 3750: 3 750# show running-config - (^) Catalyst 6509: Cat_6509(enable) show running-config
Link aggregation with Cisco Fast Ethernet switches
Some enterprise IT organizations use Cisco Fast Ethernet (100 Mbps)
network switches. In this case, they may not want to incur the
expenses to replace the Cisco Fast Ethernet switches to match the
high speed of the Dell PowerConnect 5316M Gigabit Ethernet switch,
but they probably still want to achieve the most bandwidth possible.
Because the PowerConnect 5316M switch supports auto-negotiation,
administrators do not need to perform any additional steps to connect
aggregated links to a Cisco Fast Ethernet switch if the Cisco switch’s
link aggregation ports are also set to auto-negotiation.
Figure 3. Using the show lacp-channel info command to confirm a LAG connection for a Cisco CatOS-based switch
Cat_6509> (enable) show lacp-channel info Chan Port Status Channel Admin Speed Duplex Vlan id mode group
801 2/1 connected active 395 a-1Gb a-full 1 801 2/2 connected active 395 a-1Gb a-full 1 801 2/3 connected active 395 a-1Gb a-full 1 801 2/4 connected active 395 a-1Gb a-full 1 801 2/5 connected active 395 a-1Gb a-full 1 801 2/6 connected active 395 a-1Gb a-full 1
...
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The ports in a Dell PowerConnect 5316M LAG are set to auto-
negotiation by default. If the negotiation setting of the LAG has been
changed because of a previous switch configuration, administra-
tors can use the following command to set the LAG ports back to
auto-negotiation:
5 316M(config)# interface port-channel 1 5316M(config-if)# negotiation
To set the ports on a Cisco IOS-based switch to auto-negotiation,
administrators can use the following commands:
2950(config)# interface range FastEthernet 0/1 - 3 2950(config-if)# speed auto 2950(config-if)# duplex auto
To set the ports on a Cisco CatOS-based switch to auto-negotiation,
administrators can use the following command:
Cat_6509> (enable) set port speed 2/9-11 auto
If auto-negotiation cannot be used, both the Dell PowerConnect
LAG and the Cisco switch ports in the LAG must be set to the same
speed and duplex. Intermittent link failures may occur if one switch
is in auto-negotiation mode and the other is forced to a certain
speed and duplex.
The Dell PowerConnect 5316M LAG can be forced to 100 Mbps
with the following commands:
5 316M(config)# interface port-channel 1 5316M(config-if)# no negotiation 5316M(config-if)# speed 100
In this example, the LAG is referred to in the command as
port-channel 1. The no negotiation command means
that there is no auto-negotiation on the ports in the LAG. The
speed 100 command specifies all the ports in the LAG to be 100
Mbps. Because this is a LAG configuration, and the 802.3ad stan-
dard requires all ports in a LAG to be full duplex, administrator do
not need to set the duplex to full (and in fact, cannot do so via
the PowerConnect 5316M CLI). The duplex is set to full by default
on LAG ports.
Note: This process differs from the Cisco IOS and CatOS
methods, which require that all the ports in the LAG be config-
ured to 100 Mbps and full duplex rather than setting the LAG to
100 Mbps. Configuring all ports in a LAG to 100 Mbps and full
duplex on the Dell PowerConnect 5316M switch would have no
effect because the LAG configuration takes precedence over indi-
vidual port configurations.
Administrators can use the following commands to set the ports
on the Cisco IOS-based switch to 100 Mbps and full duplex:
2950(config)# interface range FastEthernet 0/1 - 3 2950(config-if)# speed 100 2950(config-if)# duplex full
Administrators can use the following commands to set
the ports on the Cisco CatOS-based switch to 100 Mbps and
full duplex:
Cat_6509> (enable) set port speed 2/9-11 100 Cat_6509> (enable) set port duplex 2/9-11 full
Configuration limitations
Ports to be aggregated must be configured so that they are com-
patible with the link aggregation feature and with the switch to
which they will be connected. For the Dell PowerConnect 5316M,
the following limitations apply to aggregated ports (the commands
to remove the configuration are shown immediately after each
limitation):
- (^) The port cannot have an IP address defined on it: 5 316M(config)# interface Ethernet g 5316M(config-if)# no ip address - (^) The port cannot belong to another LAG: 5 316M(config)# interface Ethernet g 5316M(config-if)# no channel-group - (^) The port cannot be a mirrored port: 5 316M(config)# interface Ethernet g 5316M(config-if)# no port monitor gxx - (^) The port cannot have GARP (Generic Attributes Registration
Protocol) VLAN (virtual LAN) Registration Protocol (GVRP)
enabled:
5 316M(config)# interface Ethernet g 5316M(config-if)# no gvrp enable
- (^) The port cannot belong to an access VLAN other than the
default VLAN (1):
5 316M(config)# interface Ethernet g 5316M(config-if)# no switchport access vlan
- (^) The port cannot belong to a trunk VLAN other than the
default VLAN (1):
5 316M(config)# interface Ethernet g 5316M(config-if)# no switchport trunk native vlan
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Interoperability between Dell and Cisco switches
The standards-based link aggregation feature of the Dell PowerConnect
5316M Gigabit Ethernet switch is designed to interoperate easily
with Cisco IOS- and CatOS-based switches. By understanding the
differences in the Dell PowerConnect 5316M and Cisco CLIs and
building on the examples presented in this article, system admin-
istrators can help integrate the PowerConnect 5316M switch into
their Cisco-based networks.
Bruce Holmes is a senior test engineer in the Dell PowerConnect Group.
He has worked at Dell for two years and supports PowerConnect switches
in all phases of product development and testing. He has a B.S. in Electri-
cal Engineering from The University of Texas at Austin.
Figure 7. Cisco CatOS commands for configuring packet distribution in a LAG
Cat_6509> (enable) set port channel all distribution ip destination Cat_6509> (enable) set port channel all distribution mac destination Cat_6509> (enable) set port channel all distribution ip both Cat_6509> (enable) set port channel all distribution mac both Cat_6509> (enable) set port channel all distribution ip source Cat_6509> (enable) set port channel all distribution mac source
FOR MORE INFORMATION
Holmes, Bruce. “Network Link Aggregation Practices with the
Dell PowerEdge 1855 Blade Server.” Dell Power Solutions,
May 2005. www.dell.com/downloads/global/power/
ps2q05-20040286-Holmes-OE.pdf
Dell PowerConnect 5316M Ethernet Switch Module
User’s Guide:
support.dell.com/support/edocs/network/PC5316M/en/UG
