There are two kinds of vifs:
In a single-mode vif, only one of the interfaces in the vif is active. The other interfaces are on standby, ready to take over if the active interface fails. Failure means that the link status of the interface is down, which signals that the interface has lost connection with the switch.
There can be more than one interface on standby in a single-mode vif. If an active interface fails, your storage system randomly picks one of the standby interfaces to be the next active link. The active link is monitored and link failover is controlled by the storage system; therefore, single-mode vif does not require any switch configuration or a switch that supports link aggregation.
All interfaces in a single-mode vif share a common Media Access Control (MAC) address.
In the following figure, e0 and e1 are part of the SingleTrunk1 single-mode vif. The active interface, e0, fails. The standby e1 interface takes over and maintains the connection to the switch.
The multimode vif implementation in Data ONTAP is in compliance with IEEE 802.3ad (static). Dynamic 802.3ad, also known as Link Aggregation Control Protocol (LACP), is not supported for the multimode vifs. Additionally, Port Aggregation Protocol (PAgP), Cisco's proprietary link aggregation protocol, is not supported. Any switch that supports aggregates, but does not have control packet exchange for configuring an aggregate can be used for the multimode vifs.
In a multimode vif, all interfaces in the vif are active and share a single MAC address. This logical aggregation of interfaces provides higher throughput than a single-mode vif. Multimode vifs can recover from a failure of up to (n-1) interfaces, where n is the total number of interfaces that form the vif.
A multimode vif requires a switch that supports link aggregation over multiple switch ports. The switch is configured so that all ports to which links of a vif are connected are part of a single logical port. For information about configuring the switch, see your switch vendor's documentation. For an example of how you can configure a Cisco® Catalyst® 6500 series switch, see How to configure a Cisco Catalyst 6500 series switch for a multimode vif.
Some switches might not support link aggregation of ports configured for jumbo frames. For more information, see your switch vendor's documentation.
Several load-balancing options are available to distribute traffic among the interfaces of a multimode vif. The load-balancing schemes are discussed in detail in Load balancing in multimode vifs.
Data ONTAP is only responsible for distributing outbound traffic and does not have control over how inbound packet arrive because each end of an aggregate is responsible for controlling the distribution of its outbound traffic.
In the following figure, e0, e1, e2, and e3 are part of the MultiTrunk1 multimode vif. All four interfaces in the MultiTrunk1 multimode vif are active.
If any three of the interfaces fail, either one by one or simultaneously, your storage system still stays connected to the network.
You can configure a Cisco Catalyst 6500 series switch that has one module (installed in slot 2) and one Supervisor Engine installed (in slot 1) and is running CatOS for a multimode vif by using the set port channel command at the switch console.
The syntax of the set port channel command is as follows.
For usage guidelines and examples of the set port channel command, see the Catalyst 6500 series Command Reference.
Note
The syntax of the set port channel command is as it was available at the time of writing the Data ONTAP 7.1 MultiStore Guide. You are advised to consult your latest Catalyst documentation to ensure the validity of this information.
set port channel mod_num/port_num... [admin_group]
set port channel mod_num/port_num mode {on | off | desirable | auto} [silent | non-silent]
set port channel all distribution {ip | mac} [source | destination | both]
mod_num/port_num is the number of module and port(s).
admin_group is the number of administrative group. Valid values are 1 to 1024.
mode--Specifies the EtherChannel mode.
on--Enables and forces specified ports to channel without PAgP.
off--Prevents ports from channeling.
desirable--Sets a PAgP mode that places a port into an active negotiating state, in which the port initiates negotiations with other ports by sending PAgP packets.
auto--(Optional) Sets a PAgP mode that places a port into a passive negotiating state, in which the port responds to PAgP packets it receives, but does not initiate PAgP packet negotiation.
silent--Keyword to use with auto or desirable when no traffic is expected from the other device, to prevent the link from being reported to Spanning Tree Protocol (STP) as down.
non-silent--Keyword to use with auto or desirable when traffic is expected from the other device.
all distribution--Keyword to apply frame distribution to all ports in the switch.
ip--Keyword to specify the frame distribution method using IP address values.
mac--Keyword to specify the frame distribution method using MAC address values.
source--(Optional) Keyword to specify the frame distribution method using source address values.
destination--(Optional) Keyword to specify the frame distribution method using destination address values.
both--(Optional) Keyword to specify the frame distribution method using source and destination address values.
The default is EtherChannel, set to auto and silent on all module ports. The defaults for frame distribution are ip and both.
To configure EtherChannel on ports 2 through 5 of module installed in slot 2, enter the following command:
set port channel 2/2-5
To set the EtherChannel load-balancing feature so that IP addresses of both source and destination addresses are utilized to determine the outgoing frames, enter the following command:
set port channel all distribution ip both
To ensure that all interfaces of a multimode vif are equally utilized for outgoing traffic, the following load-balancing methods are available:
The load-balancing method to use for a multimode vif can be specified only when the vif is created. If no method is specified, the IP-address based load balancing method is used.
In both of these methods, the last byte of the source and destination address (IP address and MAC address) is used to determine the interface to use for the outgoing frame. The following formula is used:
((source_address XOR destination_address) % number_of_links)
If the result of this formula maps to an interface that is not in the UP link-state, the next active interface is used.
For example, a vif consisting of eight physical interfaces is created with the IP address-based load-balancing method. It is configured with IP address 10.0.0.10. Based on the above formula, an IP frame going through this vif to the destination IP address 172.26.15.224 will use interface #2, provided that this interface is in the UP link-state.
Note
Do not select the MAC-address based load-balancing method when creating vifs on a storage system that connects directly to a router. In such a setup, for every outgoing IP frame, the destination MAC address will be the MAC address of the router. As a result, only one interface of the vif will be used.
Unlike the IP-address and MAC-address load-balancing methods, this method provides true load balancing. This method may cause out-of-order packet delivery and retransmissions due to overruns.
This method of load balancing is recommended for clients connected in a back-to-back configuration with your storage system.
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Part No. 210-01082_B0
File: vifs3.htm
Last updated: 08-Dec-2005 13:27:19