Cisco WS-C4003 Software Guide - Page 81
Understanding Frame Distribution
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Chapter 6 Configuring Fast EtherChannel and Gigabit EtherChannel Understanding How EtherChannel Works There are four user-configurable channel modes: on, off, auto, and desirable. PAgP packets are exchanged only between ports in auto and desirable mode. Ports configured in on or off mode do not exchange PAgP packets. The auto and desirable modes can be modified with the silent and non-silent keywords. Table 6-1 describes each mode. Table 6-1 Channel Modes Mode on off auto desirable Description Forces the port to channel without negotiation. PAgP packets are not exchanged. The port is channeling regardless of how the peer port is configured. If the peer port is in on mode, a channel is formed. In any other mode, the peer port is placed in the errdisable state due to a channel misconfiguration. Prevents the port from channeling. PAgP packets are not exchanged. The port is not channeling regardless of how the peer port is configured. No channel is formed. Places a port into a passive negotiating state, in which the port responds to PAgP packets it receives but does not initiate PAgP packet negotiation. A channel is formed only with another port group in desirable mode. (Default) Places a port into an active negotiating state, in which the port initiates negotiations with other ports by sending PAgP packets. A channel is formed with another port group in either desirable or auto mode. Use the silent keyword when you are connecting to a "silent partner" (a device that is not generating BPDUs or other traffic). An example of a silent partner is a traffic generator that is not transmitting packets. Use this keyword with the auto or desirable mode. If you do not specify silent or non-silent, silent is assumed. Use the non-silent keyword when you are connecting to a device that will transmit BPDUs or other traffic. Use this keyword with the auto or desirable mode. Both the auto and desirable modes allow ports to negotiate with connected ports to determine if they can form a channel, based on criteria such as port speed, trunking state, native VLAN, and so on. Ports can form an EtherChannel when they are in different channel modes as long as the modes are compatible. For example: • A port in desirable mode can form an EtherChannel successfully with another port that is in desirable or auto mode. • A port in auto mode can form an EtherChannel with another port in desirable mode. • A port in auto mode cannot form an EtherChannel with another port that is also in auto mode, since neither port will initiate negotiation. • A port in on mode can form a channel only with a port in on mode, because ports in on mode do not exchange PAgP packets. • A port in off mode will not form a channel with any port. Understanding Frame Distribution EtherChannel distributes frames across the links in a channel based on the low-order bits of the source and destination Media Access Control (MAC) addresses of each frame. The frame distribution method is not configurable. 78-12647-02 Software Configuration Guide-Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4 6-3