Port Aggregation Protocol (PAgP)
To accommodate automated EtherChannel agreement and agreement amid switches, Cisco
developed the Anchorage Aggregation Protocol (PAgP). PAgP packets are exchanged between
switches over EtherChannel-capable ports. The identification of neighbors and anchorage group
capabilities are abstruse and are compared with bounded about-face capabilities. Ports that accept the
same acquaintance accessory ID and anchorage accumulation adequacy will be arranged calm as a bidirectional,
point-to-point EtherChannel link.
PAgP will anatomy an EtherChannel alone on ports that are configured for either identical static
VLANs or trunking. PAgP additionally dynamically modifies ambit of the EtherChannel if one of
the arranged ports is modified. For example, if the VLAN, speed, or bifold approach of a anchorage in an
established array is changed, PAgP will change that constant for all ports in the bundle.
When ports are arranged into an EtherChannel, all broadcasts and multicasts are beatific over one
port in the array only. Broadcasts will not be beatific over the actual ports and will not be
allowed to acknowledgment over any added anchorage in the bundle.
Switch ports can be configured for the afterward modes of PAgP:
• On—The ports will consistently be arranged as an EtherChannel. No agreement takes place
because PAgP packets are not beatific or processed.
• Off—The ports will never be arranged as an EtherChannel. They will abide as individual
access or block links. No PAgP packets are sent.
• Auto—(Default) PAgP packets are beatific to accommodate an EtherChannel alone if the far end
initiates EtherChannel negotiations. Therefore, auto approach is a acquiescent approach that requires
a acquaintance in adorable mode. (Two switches in auto approach will never accommodate an
EtherChannel because anniversary is irenic cat-and-mouse for the added to appeal an EtherChannel.)
• Desirable—PAgP packets are beatific to actively accommodate an EtherChannel. This mode
starts the agreement process, and will accompany up a acknowledged EtherChannel with another
switch in either adorable or auto mode.