34-5
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 34 Configuring EtherChannels and Link-State Tracking
Understanding EtherChannels
PAgP Modes
Table 34-1
shows the user-configurable EtherChannel PAgP modes for the
channel-group
interface
configuration command on an NNI or ENI.
Switch ports exchange PAgP packets only with partner ports configured in the
auto
or
desirable
modes.
Ports configured in the
on
mode do not exchange PAgP packets.
Both the
auto
and
desirable
modes enable ports to negotiate with partner ports to form an EtherChannel
based on criteria such as port speed and, for Layer 2 EtherChannels, trunking state and VLAN numbers.
Ports can form an EtherChannel when they are in different PAgP modes as long as the modes are
compatible. For example:
•
A port in the
desirable
mode can form an EtherChannel with another port that is in the
desirable
or
auto
mode.
•
A port in the
auto
mode can form an EtherChannel with another port that is in the
desirable
mode.
A port in the
auto
mode cannot form an EtherChannel with another port that is also in the
auto
mode
because neither port starts PAgP negotiation.
If your switch is connected to a partner that is PAgP-capable, you can configure the switch port for
nonsilent operation by using the
non-silent
keyword. If you do not specify
non-silent
with the
auto
or
desirable
mode, silent mode is assumed.
Use the silent mode when the switch is connected to a device that is not PAgP-capable and seldom, if
ever, sends packets. An example of a silent partner is a file server or a packet analyzer that is not
generating traffic. In this case, running PAgP on a physical port connected to a silent partner prevents
that switch port from ever becoming operational. However, the silent setting allows PAgP to operate, to
attach the port to a channel group, and to use the port for transmission.
PAgP Interaction with Other Features
Cisco Discovery Protocol (CDP) sends and receives packets over the physical ports in the EtherChannel.
Note
PAgP and CDP are only available on NNIs and ENIs. User network interfaces (UNIs) do not
support PAgP or CDP.
Trunk ports send and receive PAgP protocol data units (PDUs) on the lowest numbered VLAN.
Table 34-1
EtherChannel PAgP Modes
Mode
Description
auto
Places a port into a passive negotiating state in which the port responds to PAgP packets it
receives but does not start PAgP packet negotiation. This setting minimizes the
transmission of PAgP packets.
desirable
Places a port into an active negotiating state in which the port starts negotiations with other
ports by sending PAgP packets.
Содержание ME 3400 Series
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