Link Aggregation according to IEEE 802.3ad
1 Why Link Aggregation?
Link Aggregation or trunking is a method of combining physical network links into a single
logical link for increased bandwidth. With Link aggregation we are able to increase the ca-
pacity and availability of the communications channel between devices (both switches and
end stations) using existing Fast Ethernet and Gigabit Ethernet technology. Two or more Gi-
gabit Ethernet connections are combined in order to increase the bandwidth capability and to
create resilient and redundant links. A set of multiple parallel physical links between two de-
vices is grouped together to form a single logical link.
Link Aggregation also provides load balancing where the processing and communications
activity is distributed across several links in a trunk so that no single link is overwhelmed.
By taking multiple LAN connections and treating them as a unified, aggregated link, we can
achieve practical benefits in many applications.
Link Aggregation provides the following important benefits:
· Higher link availability
· Increased link capacity
· Improvements are obtained using existing hardware (no upgrading to higher-capacity
link technology is necessary)
Higher Link Availability
Link aggregation prevents the failure of any single component link from leading to a disrup-
tion of the communications between the interconnected devices. The loss of a link within an
aggregation reduces the available capacity but the connection is maintained and the data
flow is not interrupted.
Increased Link Capacity
The performance is improved because the capacity of an aggregated link is higher than each
individual link alone.
Standard LAN technology provides data rates of 10 Mb/s, 100 Mb/s, and 1000 Mb/s. Link
Aggregation can fill the gaps of these available data rates when an intermediate perform-
ance level is more appropriate; a factor of 10 increase may be overkill in some environ-
ments.
If a higher capacity than 1000 Mb/s is needed, the user can group several SysKonnect
1000 Mb/s adapters together to form a high speed connection and additionally benefit from
the failover function the SysKonnect driver for Link Aggregation supports. This provides mi-
gration to 10 Gigabit Ethernet solutions which are not yet available.
Aggregating replaces Upgrading
If the link capacity is to be increased, there are usually two possibilities: either upgrade the
native link capacity or use an aggregate of two or more lower-speed links (if provided by the
card ’s manufacturer). Upgrades typically occur in factors of 10. In many cases, however, the
device cannot take advantage of this increase. A performance improvement of 1:10 is not
achieved, moreover the bottleneck is just moved from the network link to some other ele-
ment within the device. Thus, the performance will always be limited by the weakest link, the
end-to-end connection.