Users Guide

11–QLogic Teaming Services
Executive Summary
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Generic Trunking
Generic Trunking is a switch-assisted teaming mode and requires configuring
ports at both ends of the link: server interfaces and switch ports. This port
configuration is often referred to as Cisco Fast EtherChannel or Gigabit
EtherChannel. In addition, generic trunking supports similar implementations by
other switch OEMs such as Extreme Networks Load Sharing and Bay Networks or
IEEE 802.3ad Link Aggregation static mode. In this mode, the team advertises
one MAC Address and one IP Address when the protocol stack responds to ARP
Requests. In addition, each physical adapter in the team uses the same team
MAC address when transmitting frames. Use of the address is possible because
the switch at the other end of the link is aware of the teaming mode and will
handle the use of a single MAC address by every port in the team. The forwarding
table in the switch will reflect the trunk as a single virtual port.
In this teaming mode, the intermediate driver controls load balancing and failover
for outgoing traffic only, while incoming traffic is controlled by the switch firmware
and hardware. As is the case for Smart Load Balancing, the QLASP intermediate
driver uses the IP/TCP and UDP source and destination addresses to load
balance the transmit traffic from the server. Most switches implement an XOR
hashing of the source and destination MAC address.
Link Aggregation (IEEE 802.3ad LACP)
Link aggregation is similar to generic trunking except that it uses the link
aggregation control protocol (LACP) to negotiate the ports that will make up the
team. LACP must be enabled at both ends of the link for the team to be
operational. If LACP is not available at both ends of the link, 802.3ad provides a
manual aggregation that only requires both ends of the link to be in a link up state.
Because manual aggregation provides for the activation of a member link without
performing the LACP message exchanges, it should not be considered as reliable
and robust as an LACP negotiated link. LACP automatically determines which
member links can be aggregated and then aggregates them. It provides for the
controlled addition and removal of physical links for the link aggregation so that no
frames are lost or duplicated. The removal of aggregate link members is provided
by the marker protocol that can be optionally enabled for Link Aggregation Control
Protocol (LACP) enabled aggregate links.
The Link Aggregation group advertises a single MAC address for all the ports in
the trunk. The MAC address of the Aggregator can be the MAC addresses of one
of the MACs that make up the group. LACP and marker protocols use a multicast
destination address.
NOTE
Generic trunking is not supported on iSCSI offload adapters.