About Channel Group Creation - Cisco Nexus 5000 Series Configuration Manual

Configuring SAN Port Channels
The port channel protocol expands the port channel functional model in Cisco SAN switches. It uses the
exchange peer parameters (EPP) services to communicate across peer ports in an ISL. Each switch uses the
information received from the peer ports along with its local configuration and operational values to decide
if it should be part of a SAN port channel. The protocol ensures that a set of ports are eligible to be part of
the same SAN port channel. They are only eligible to be part of the same port channel if all the ports have a
compatible partner.
The port channel protocol uses two subprotocols:
• Bringup protocol—Automatically detects misconfigurations so you can correct them. This protocol
synchronizes the SAN port channel at both ends so that all frames for a given flow (as identified by the
source FC ID, destination FC ID and OX_ID) are carried over the same physical link in both directions.
This helps make applications such as write acceleration work for SAN port channels over FCIP links.
• Autocreation protocol—Automatically aggregates compatible ports into a SAN port channel.

About Channel Group Creation

If channel group autocreation is enabled, ISLs can be configured automatically into channel groups without
manual intervention. The following figure shows an example of channel group autocreation.
The first ISL comes up as an individual link. In the example shown in the following figure, this is link A1-B1.
When the next link comes up (A2-B2 in the example), the port channel protocol determines if this link is
compatible with link A1-B1 and automatically creates channel groups 10 and 20 in the respective switches.
Link A3-B3 can join the channel groups (and the port channels) if the respective ports have compatible
configurations. Link A4-B4 operates as an individual link, because it is not compatible with the existing
member ports in the channel group.
Figure 26: Autocreating Channel Groups
The channel group numbers are assigned dynamically (when the channel group is formed).
The channel group number may change across reboots for the same set of port channels depending on the
initialization order of the ports.
The following table identifies the differences between user-configured and auto-configured channel groups.
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Cisco Nexus 5000 Series NX-OS SAN Switching Configuration Guide, Release 5.2(1)N1(1)
SAN Port Channel Protocol
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