Configuring Trunk Groups and Dynamic Link Aggregation
December 2005
© Foundry Networks, Inc.
10 - 15
NOTE:
Use the link aggregation feature only if the device at the other end of the link 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 Foundry 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 Foundry 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 Foundry port can exchange
LACPDU messages with the port at the remote end of the link, but the Foundry 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:
Foundry 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.
Configuration Notes
•
You cannot use 802.3ad link aggregation on a port configured as a member of a static trunk group.
•
This feature is supported only on Gigabit Ethernet ports.
•
The dynamic link aggregation (802.3ad) implementation on the FESX, FSX, and FWSX allow any number of
ports up to four to be aggregated into a link. The feature does not require the aggregate link to consist of
exactly two or four ports.
•
When the feature dynamically adds or changes a trunk group, the
show trunk
command displays the trunk
as both configured and active. However, the
show running-config
or
write terminal
command does not
contain a trunk command defining the new or changed trunk group.
•
If the feature places a port into a trunk group as a secondary port, all configuration information except
information related to link aggregation is removed from the port. For example, if port 1/3 has an IP interface,
and the link aggregation feature places port 1/3 into a trunk group consisting of ports 1/1 – 1/4, the IP
interface is removed from the port.
•
If you use this feature on a Layer 3 Switch that is running OSPF or BGP4, the feature causes these protocols
to reset when a dynamic link change occurs. The reset includes ending and restarting neighbor sessions with
OSPF and BGP4 peers, and clearing and relearning dynamic route entries and forwarding cache entries.
Although the reset causes a brief interruption, the protocols automatically resume normal operation.
•
You can enable link aggregation on 802.1Q tagged ports (ports that belong to more than one port-based
VLAN).
•
Dynamic Operation of Allocation Keys (section 43.6.2 in the 802.3ad specification) is supported.
•
The trunks that will be formed by link aggregation will strictly adhere to the static trunking rules on the
FastIron family of switches. Be careful in selecting keys if you are manually configuring link aggregation keys.
Make sure that the possible trunks that you expect to be formed conform to the static trunking rules.
Adaptation to Trunk Disappearance
The Foundry 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. Once the other device recovers, 802.3 can
renegotiate the link without a mismatch.
Содержание FastIron Edge Switch X424
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