Cisco Nexus devices implement VSAN trunking and port channels as follows:

• A SAN port channel enables several physical links to be combined into one aggregated logical link.

• An industry standard E port can link to other vendor switches and is referred to as inter-switch link (ISL), as shown on the left side of the figure below.

• VSAN trunking enables a link transmitting frames in the EISL format to carry traffic for multiple VSAN . When trunking is operational on an E port, that E port becomes a TE port. EISLs connects only between Cisco switches, as shown on the right side of the figure below.

  

• You can create a SAN port channel with members that are E ports, as shown on the left side of the figure below. In this configuration, the port channel implements a logical ISL (carrying traffic for one VSAN).

• You can create a SAN port channel with members that are TE-ports, as shown on the right side of the figure below. In this configuration, the port channel implements a logical EISL (carrying traffic for multiple VSANs).

  

• Port channel interfaces can be channeled between the following port sets:

  • E ports and TE ports

  • F ports and NP ports

  • TF ports and TNP ports

• Trunking permits traffic on multiple VSANs between switches.

• Port channels and trunking can be used between TE ports over EISLs.

Load-balancing functionality can be provided using the following methods:

• Flow based—All frames between source and destination follow the same links for a given flow. That is, whichever link is selected for the first exchange of the flow is used for all subsequent exchanges.

• Exchange based—The first frame in an exchange is assigned to a link, and then subsequent frames in the exchange follow the same link. However, subsequent exchanges can use a different link. This method provides finer granularity for load balancing while preserving the order of frames for each exchange.

The following figure illustrates how flow-based load balancing works. When the first frame in a flow is received on an interface for forwarding, link 1 is selected. Each subsequent frame in that flow is sent over the same link. No frame in SID1 and DID1 utilizes link 2.

The following figure illustrates how exchange-based load balancing works. When the first frame in an exchange is received for forwarding on an interface, link 1 is chosen by a hash algorithm. All remaining frames in that particular exchange are sent on the same link. For exchange 1, no frame uses link 2. For the next exchange, link 2 is chosen by the hash algorithm. Now all frames in exchange 2 use link 2.

Before configuring a SAN port channel, consider the following guidelines:

• Port-channel mode is active by default. Port-channel ON mode is not supported.

• Configure SAN port Channel using Fibre Channel ports from different port groups.

• Ensure that one SAN port channel is not connected to different sets of switches. SAN port channels require point-to-point connections between the same set of switches.

• If you misconfigure SAN port channels, you may receive a misconfiguration message. If you receive this message, the port channel’s physical links are disabled because an error has been detected.

• If the following requirements are not met, a SAN port channel error is detected:

  • Each switch on either side of a SAN port channel must be connected to the same number of interfaces.

  • Each interface must be connected to a corresponding interface on the other side.

  • Links in a SAN port channel cannot be changed after the port channel is configured. If you change the links after the port channel is configured, be sure to reconnect the links to interfaces within the port channel and reenable the links.

    If all three conditions are not met, the faulty link is disabled.

Enter the show interface command for that interface to verify that the SAN port channel is functioning as required.

You can configure each SAN port channel with a channel group mode parameter to determine the port channel protocol behavior for all member ports in this channel group. The possible values for a channel group mode are as follows:

• On (default)—The member ports only operate as part of a SAN port channel or remain inactive. In this mode, the port channel protocol is not initiated. However, if a port channel protocol frame is received from a peer port, the software indicates its nonnegotiable status. Port channels configured in the On mode require you to explicitly enable and disable the port channel member ports at either end if you add or remove ports from the port channel configuration. You must physically verify that the local and remote ports are connected to each other.

• Active—The member ports initiate port channel protocol negotiation with the peer port(s) regardless of the channel group mode of the peer port. If the peer port, while configured in a channel group, does not support the port channel protocol, or responds with a nonnegotiable status, it will default to the On mode behavior. The Active port channel mode allows automatic recovery without explicitly enabling and disabling the port channel member ports at either end.

  Note	A F port channel is supported only in Active Mode.

The table below compares On and Active modes.

When you delete the SAN port channel, the corresponding channel membership is also deleted. All interfaces in the deleted SAN port channel convert to individual physical links. After the SAN port channel is removed, regardless of the mode (active and on) used, the ports at either end are gracefully brought down, indicating that no frames are lost when the interface is going down.

If you delete the SAN port channel for one port, then the individual ports within the deleted SAN port channel retain the compatibility parameter settings (speed, mode, port VSAN, allowed VSAN, and port security). You can explicitly change those settings as required.

• If you use the default On mode to avoid inconsistent states across switches and to maintain consistency across switches, then the ports shut down. You must explicitly enable those ports again.

• If you use the Active mode, then the port channel ports automatically recover from the deletion.

You can add a physical interface (or a range of interfaces) to an existing SAN port channel. The compatible parameters on the configuration are mapped to the SAN port channel. Adding an interface to a SAN port channel increases the channel size and bandwidth of the SAN port channel.

After the members are added, regardless of the mode (Active and On) used, the ports at either end are gracefully brought down, indicating that no frames are lost when the interface is going down.

For adding Fibre channel (FC) Breakout (BO) interfaces to a SAN Port channel on Cisco Nexus N9K-C9336C-FX2-E platform switch, see SAN Switching General Guidelines and Limitations.

When a physical interface is deleted from the SAN port channel, the channel membership is automatically updated. If the deleted interface is the last operational interface, then the port channel status is changed to a down state. Deleting an interface from a SAN port channel decreases the channel size and bandwidth of the SAN port channel.

• If you use the default On mode to avoid inconsistent states across switches and to maintain consistency across switches, then the ports shut down. You must explicitly enable those ports again.

• If you use the Active mode, then the port channel ports automatically recover from the deletion.

After the members are deleted, regardless of the mode (Active and On) used, the ports at either end are gracefully brought down, indicating that no frames are lost when the interface is going down.

A user-configured channel group cannot be converted to an autocreated channel group. However, you can convert an autocreated channel group to a manual channel group. This task is irreversible. The channel group number does not change, but the member ports operate according to the properties of the manually configured channel group, and channel group autocreation is implicitly disabled for all the member ports.

If you enable persistence, be sure to enable it at both ends of the SAN port channel.