Link Aggregation Group (LAG) Dell Switch Side

A Link Aggregated Group (LAG), combines individual physical links into one logical channel to increase the total bandwidth and give the logical channel redundancy. This feature goes by different names from vendor to vendor, Port Channel, and Aggregated Ethernet (EA) are just a few of the names.

It also is seen as one link by Spanning Tree, this reduces the number of topology changes when link state change, and gains the full bandwidth of the individual interfaces.

Other terms used to describe the method include port trunking, link bundlingNetwork/NIC bonding, or NIC teaming. These terms encompass not only vendor-independent standards such as Link Aggregation Control Protocol (LACP) for Ethernet defined in IEEE 802.1AX and IEEE 802.1aq or the previous IEEE 802.3ad, but also various proprietary solutions (EtherChannel, PAgP).

A Port channel is the logical representation of the aggregated link on the switch. Once configured, you make your changes on the port channel interface and these will be automatically applied to all the individual interfaces within the group. For example, if this interface were to be a General or Trunk mode, configure the port-channel interface as required to put it in the proper mode to match the other side of the port-channel, and configure as required (add or remove VLANs from the trunk).

A switch Port-channel interface will decide which member link to send frames based on the algorithm output, performed against one or more fields of each frame. Which fields depend on the switch platform and configuration. There are different sorting algorithms that can be used. Note, only sending is subject to the algorithm, the device depends on the sending end to load balance using the matching algorithm.

In this example we add four (4) interfaces from two (2) switches in a stack to a single port-channel. 4-2-1 as it were.

console(config)#interface gi 1/0/1
console(config-if)#channel-group 2 mode active
console(config-if)#interface gi 1/0/2
console(config-if)#channel-group 2 mode active
console(config-if)#interface gi 2/0/1
console(config-if)#channel-group 2 mode active
console(config-if)#interface gi 2/0/2
console(config-if)#channel-group 2 mode active

Once you have added some interfaces to the channel group, show interface port-channel 2 should indicate active ports, if we have done everything correctly.

console#show interfaces port-channel 1

Channel   Ports                         Ch-Type  Hash Type Min-links Local Prf
-------   ----------------------------- -------- --------- --------- ---------
Po1       Active: Gi1/0/1, Gi1/0/2,     Dynamic  7         1         Disabled
          Gi2/0/1, Gi2/0/2

Hash Algorithm Type
1 - Source MAC, VLAN, EtherType, source module and port Id
2 - Destination MAC, VLAN, EtherType, source module and port Id
3 - Source IP and source TCP/UDP port
4 - Destination IP and destination TCP/UDP port
5 - Source/Destination MAC, VLAN, EtherType, source MODID/port
6 - Source/Destination IP and source/destination TCP/UDP port
7 - Enhanced hashing mode

Make sure to remove any interface configuration that might affect the joining of a channel group. show running-config interface gi 1/0/1, for example, will give you the current interface configuration of gi 1/0/1. Should be a pretty bare configuration on the channel group interfaces.

console#show running-config interface gi 1/0/1
channel-group 2 mode active

Verify the configuration of the port-channel

console#show running-config interface port-channel 1
switchport mode general
switchport general vlan add 26 tagged
switchport general vlan remove 1

The other end of the port channel will require a mirror configuration. In our example, an LACP-enabled port channel with trunking to another switch. But configure to suit your situation.

The other end doesn’t necessarily have to be a physical switch, VMware Distributed Virtual Switches (dvSwitch for short) can also be configured to use LACP LAGs (Only available on Distributed Switch Enterprise license and above).

Aug 3rd, 2016 • Posted in Dell, STP, Switching, VLAN, VMware
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