IBM 12.1(22)EA6 User Manual
24-5
Cisco Systems Intelligent Gigabit Ethernet Switch Modules for the IBM BladeCenter, Software Configuration Guide
24R9746
Chapter 24 Configuring EtherChannels and Layer 2 Trunk Failover
Understanding EtherChannels
Exchanging LACP Packets
Both the active and passive LACP modes allow interfaces to negotiate with partner interfaces to
determine if they can form an EtherChannel based on criteria such as interface speed and, for Layer 2
EtherChannels, trunking state, and VLAN numbers.
determine if they can form an EtherChannel based on criteria such as interface speed and, for Layer 2
EtherChannels, trunking state, and VLAN numbers.
Interfaces can form an EtherChannel when they are in different LACP modes as long as the modes are
compatible. For example:
compatible. For example:
•
An interface in the active mode can form an EtherChannel with another interface that is in the active
mode.
mode.
•
An interface in the active mode can form an EtherChannel with another interface in the passive
mode.
mode.
An interface in the passive mode cannot form an EtherChannel with another interface that is also in the
passive mode because neither interface starts LACP negotiation.
passive mode because neither interface starts LACP negotiation.
Note
An EtherChannel cannot be configured in both the PAgP and LACP modes.
Physical Learners and Aggregate-Port Learners
Network devices are classified as PAgP physical learners or aggregate-port learners. A device is a
physical learner if it learns addresses by physical ports and directs transmissions based on that
knowledge. A device is an aggregate-port learner if it learns addresses by aggregate (logical) ports.
physical learner if it learns addresses by physical ports and directs transmissions based on that
knowledge. A device is an aggregate-port learner if it learns addresses by aggregate (logical) ports.
When a device and its partner are both aggregate-port learners, they learn the address on the logical
port-channel. The device sends packets to the source by using any of the interfaces in the EtherChannel.
With aggregate-port learning, it is not important on which physical port the packet arrives.
port-channel. The device sends packets to the source by using any of the interfaces in the EtherChannel.
With aggregate-port learning, it is not important on which physical port the packet arrives.
The switch uses source-MAC address distribution for a channel if it is connected to a physical learner
even if you configure the switch for destination-MAC address distribution.
even if you configure the switch for destination-MAC address distribution.
These frame distribution mechanisms are possible for frame transmission:
•
Load distribution based on the source-MAC address of the packet
•
Load distribution based on the destination-MAC address of the packet
•
Load distribution based on the XOR of the source-MAC address and destination-MAC address
•
Load distribution based on the source-host IP address
•
Load distribution based on the destination-host IP address
•
Load distribution based on the XOR of the source-IP address and destination-IP address
The switch supports up to eight ports in a PAgP group.
PAgP and LACP Interaction with Other Features
The Dynamic Trunking Protocol (DTP) and Cisco Discovery Protocol (CDP) send and receive packets
over the physical interfaces in the EtherChannel. Trunk ports send and receive PAgP and LACP protocol
data units (PDUs) on the lowest numbered VLAN.
over the physical interfaces in the EtherChannel. Trunk ports send and receive PAgP and LACP protocol
data units (PDUs) on the lowest numbered VLAN.
Spanning tree sends packets over a single physical interface in the EtherChannel, regarding the
EtherChannel as one port.
EtherChannel as one port.