Understanding Etherchannel Port Grouping; Port Group Restrictions On Static-Address Forwarding - Cisco WS-C2955T-12 Software Manual

Creating EtherChannel Port Groups

Understanding EtherChannel Port Grouping

This software release supports two different types of port groups: source-based forwarding port groups
and destination-based forwarding port groups.
Source-based forwarding port groups distribute packets forwarded to the group based on the source
address of incoming packets. You can configure up to eight ports in a source-based forwarding port
group. Source-based forwarding is enabled by default.
Destination-based port groups distribute packets forwarded to the group based on the destination address
of incoming packets. You can configure an unlimited number of ports in a destination-based port group.
You can create up to 12 port groups. All ports in each group must be of the same type; for example, they
must be all source-based or all destination-based. You can have source-based port groups and
destination-based source groups. You can independently configure port groups that link switches, but
you must consistently configure both ends of a port group.
In Figure
single-MAC-address device, source-based forwarding ensures that the switch uses all available
bandwidth to the router. The router is configured for destination-based forwarding because the large
number of stations ensures that the traffic is evenly distributed through the port-group ports on the router.
Figure 7-1
The switch treats the port group as a single logical port; therefore, when you create a port group, the
switch uses the configuration of the first port for all ports added to the group. If you add a port and
change the forwarding method, it changes the forwarding for all ports in the group. After the group is
created, changing STP or VLAN membership parameters for one port in the group automatically changes
the parameters for all ports. Each port group has one port that carries all unknown multicast, broadcast,
and STP packets.

Port Group Restrictions on Static-Address Forwarding

These restrictions apply to entering static addresses that are forwarded to port groups:
•
•
Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
7-8
7-1, a port group of two workstations communicates with a router. Because the router is a
Source-Based Forwarding
Source-based
forwarding
Catalyst 2900 XL
or Catalyst 3500 XL switch
If the port group forwards based on the source MAC address (the default), configure the static
address to forward to all ports in the group. This method eliminates the chance of lost packets.
If the port group forwards based on the destination address, configure the static address to forward
to only one port in the port group. This method avoids the possible transmission of duplicate
packets. For more information, see the
Destination-based
forwarding
FEC port group
Cisco router
"Adding Static Addresses" section on page
Chapter 7 Configuring the Switch Ports
6-19.
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