Cisco Catalyst 4500 Series, Software Configuration Manual

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 27 Configuring EtherChannel and Link State Tracking
EtherChannel Configuration Guidelines and Restrictions
LACP tries to configure the maximum number of compatible ports in an EtherChannel up to the
maximum allowed by the hardware (eight ports). If a port cannot be actively included in a channel, it is
not included automatically if a channeled port fails.
You can change the LACP timer rate to modify the duration of the LACP timeout. Use the
lacp rate
command to set the rate at which LACP control packets are sent to an LACP-supported interface. You
can change the timeout rate from the default rate (30 seconds) to the fast rate (1 second). This command
is supported only on LACP-enabled interfaces. To configure the LACP fast time rate, see Configuring
the LACP Fast Timer Rate.
ISSU and stateful switchover cannot be guaranteed with LACP fast timers.
Note
Standby and “sub-channeling” are not supported in LACP and PAgP.
Load Balancing
EtherChannel can balance the traffic load across the links in the channel by reducing part of the binary
pattern formed from the addresses or ports in the frame to a numerical value that selects one of the links
in the channel. To balance the load, EtherChannel uses MAC addresses, IP addresses, or Layer 4 port
numbers, and either the message source or message destination, or both.
Use the option that provides the greatest variety in your configuration. For example, if the traffic on a
channel is going only to a single MAC address, using the destination MAC address always chooses the
same link in the channel; using source addresses or IP addresses might result in better load balancing.
Note
Load balancing can only be configured globally. As a result, all channels (manually configured, PagP,
or LACP) use the same load-balancing method.
For additional information on load balancing, see the “Configuring EtherChannel Load Balancing”
section on page 27-18 .
EtherChannel Configuration Guidelines and Restrictions
If improperly configured, some EtherChannel interfaces are disabled automatically to avoid network
loops and other problems. Follow these guidelines and restrictions to avoid configuration problems:
•
All Ethernet interfaces on all modules support EtherChannel (maximum of eight interfaces) with no
requirement that interfaces be physically contiguous or on the same module.
•
Configure all interfaces in an EtherChannel to operate at the same speed and duplex mode.
•
Enable all interfaces in an EtherChannel. Disabling an interface in an EtherChannel is treated as a
link failure, and its traffic is transferred to one of the remaining interfaces in the EtherChannel.
•
An EtherChannel does not form if one of the interfaces is a Switched Port Analyzer (SPAN)
destination port.
•
For Layer 3 EtherChannels:
–
Assign Layer 3 addresses to the port channel logical interface, not to the physical interfaces in
the channel.
• For Layer 2 EtherChannels: