PAgP Modes
Catalyst 2950 Desktop Switch Software Configuration Guide j
Table 25-1 EtherChannel Modes
Mode Description auto Places an interface into a passive negotiating state, in which the interface responds to PAgP
packets it receives but does not initiate PAgP packet negotiation. This setting minimizes the transmission of PAgP packets.
desirable Places an interface into an active negotiating state, in which the interface initiates negotiations with other interfaces by sending PAgP packets.
on Forces the interface to channel without PAgP. With the on mode, a usable EtherChannel exists only when an interface group in the on mode is connected to another interface group in the on mode.
Both the auto and desirable modes allow interfaces to negotiate with partner interfaces to determine if they can form an EtherChannel based on criteria such as interface speed and, for Layer 2 EtherChannels, trunking state and VLAN numbers.
Interfaces can form an EtherChannel when they are in different PAgP modes as long as the modes are compatible. For example:
♦ An interface in desirable mode can form an EtherChannel with another interface that is in desirable or auto mode.
♦ An interface in auto mode can form an EtherChannel with another interface in desirable mode.
♦ An interface in auto mode cannot form an EtherChannel with another interface that is also in auto mode because neither interface initiates PAgP negotiation.
An interface in the on mode that is added to a port channel is forced to have the same characteristics as the already existing on mode interfaces in the channel.
Caution You should exercise care when setting the mode to on (manual configuration). All ports configured in the on mode are bundled in the same group and are forced to have similar characteristics. If the group is misconfigured, packet loss or STP loops might occur.
If your switch is connected to a partner that is PAgP-capable, you can configure the switch interface 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.
The silent mode is used when the switch is connected to a device that is not PAgP-capable and seldom, if ever, transmits 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 interface to a channel group, and to use the interface for transmission.
Continue reading here: Configuring the PAgP Learn Method and Priority
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