HP ProCurve 9304M Installation And Configuration Manual page 194

Installation and Basic Configuration Guide
NOTE: Use the link aggregation feature only if the device at the other end of the links you want to aggregate also
supports IEEE 802.3ad link aggregation. Otherwise, you need to manually configure the trunk links.
Link aggregation support is disabled by default. You can enable the feature on an individual port basis, in active or
passive mode.
• Active mode – When you enable a port for active link aggregation, the HP port can exchange standard LACP
Protocol Data Unit (LACPDU) messages to negotiate trunk group configuration with the port on the other side
of the link. In addition, the HP port actively sends LACPDU messages on the link to search for a link
aggregation partner at the other end of the link, and can initiate an LACPDU exchange to negotiate link
aggregation parameters with an appropriately configured remote port.
• Passive mode – When you enable a port for passive link aggregation, the HP port can exchange LACPDU
messages with the port at the remote end of the link, but the HP port cannot search for a link aggregation port
or initiate negotiation of an aggregate link. Thus, the port at the remote end of the link must initiate the
LACPDU exchange.
NOTE: HP recommends that you disable or remove the cables from the ports you plan to enable for dynamic link
aggregation. Doing so prevents the possibility that LACP will use a partial configuration to talk to the other side of
a link. A partial configuration does not cause errors, but does sometimes require LACP to be disabled and re-
enabled on both sides of the link to ensure that a full configuration is used. It's easier to disable a port or remove
its cable first. This applies both for active link aggregation and passive link aggregation.
802.3ad Enhancements in Release 07.6.04
Software release 07.6.04 contains the following enhancements to 802.3ad support:
• Adaptation to trunk disappearance. The HP device will tear down an aggregate link if the device at the other
end of the link reboots or brings all the links down. Tearing the aggregate link down prevents a mismatch if
the other device has a different trunk configuration following the reboot or re-establishment of the links.
• The criteria for being eligible to be in an aggregate link are more flexible. A range of ports can contain down
ports and still be eligible to become an aggregate link.
Adaptation to Trunk Disappearance
Release 07.6.04 prevents trunk mismatches caused when one device changes the number of ports in group of
ports that has become part of an 802.3 aggregate link. In 07.6.04 and later, if a device changes the number of
ports in an active aggregate link, the HP device on the other end of the link tears down the link. Once the other
device recovers, 802.3 can renegotiate the link without a mismatch.
In previous releases, it is possible for a trunk mismatch to occur between two devices that have established an
aggregate link. This can occur if one of the devices reboots or brings the trunk links down, then re-establishes the
links but with a different number of trunk ports. Figure 7.8 shows an example.
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