Technical information

39 EqualLogic Configuration Guide | Version 15.2 | August 2014
Table 14 Link aggregation types
Link aggregation type
Notes
Static
Static link aggregation defines a set of links that provide a point to point
connection between two switches. These links may or may not provide failover
redundancy or traffic load management.
LACP
Link Aggregation Control Protocol is based on IEEE 802.3ad or IEEE 802.1AX.
LACP is a dynamic LAG technology that automatically adjusts to the
appearance or disappearance of links within the defined LACP group.
PAgP
Port Aggregation Protocol (PAgP) is a Cisco Systems® proprietary networking
protocol, which is used for the automated, logical aggregation of Ethernet
switch ports, known as an etherchannel. This means it can only be used
between Cisco switches and/or switches from licensed vendors.
Vendor Proprietary
Several switch vendors may provide additional link aggregation options that are
completely proprietary or may be extensions to one of the two previously
mentioned solutions. In most cases, this type of link aggregation solution is
designed to reduce or eliminate the need – and the overhead – of the
Spanning Tree Protocol that must be used in the two previous options. If
available, these proprietary options should be considered. They may be very
useful in allowing the network administrator to create a more efficient multi-
switch layer 2 network infrastructure for a SAN. Be aware that these proprietary
solutions must support the transmission of IEEE 802.1x flow control and jumbo
frames (if used) to properly support an EqualLogic SAN.
Examples of this type of interconnect include Dell Networking or Force10
Virtual Link Trunking (VLT) and Cisco Virtual Port Channel (VPC).
8.2.1.3 Using a LAG to Connect Stacked Switches
In some situations it may become necessary to expand the EqualLogic SAN by using more than one single
switch stack. For example, you can link multiple stacks by creating a multi-link LACP based LAG between
the switch stacks. A simplified stack plus LAG switch configuration is illustrated in Figure 5. You should
consider the following recommendations when designing this type of SAN:
 If possible, use 10Gb or higher connections for all links between each stack.
 Distribute the links across multiple switches within each stack.
 Use LACP or another type of dynamic link aggregation protocol.
 Perform tests to determine the best hashing algorithm to use within the LAG (port channel).
Note: A multi-stack SAN infrastructure as described in this section may provide added reliability to the
SAN environment. But, it may also introduce additional latency and the potential for lower throughput.
The SAN designer will have to carefully consider the performance and reliability implications.