本帖最后由 blakegao 于 2015-3-13 16:16 编辑 当我们针对PAgP进行配置时，可以选择silent和non-silent两种子模式，由于网上关于这两个关键字的资料较少，所以在此说明一下：
Non-Silent:只有在etherchannel的两端都可以进行收发数据的情况下，bundle才能建立起来。防止了单向链路的情况发生。
Silent:在没有确认两端是否都可以进行收发数据的情况下，channel就能建立。可以依靠UDLD之类的其他特性来保证链路的完整性。如果我们配置了auto silent 模式，那么我们将告诉交换机，只要由对端进行发起，比如对端是desirable，那么channel就可以建立成功。但是这种情况下交换机并不会check链路的单向问题。如果配置了auto non-silent模式，那么交换机首先会check链路的单向性然后有对端发起并建立channel。官方推荐一般不要修改默认配置，一般情况下，auto默认是silent模式，desirable默认是non-slient模式。
(config-if)#channel-groupchannel-group-number mode {auto[non-silent] |desirable [non-silent] | on} | {active| passive}http://www.cisco.com/c/en/us/td/ ... 50scg/swethchl.html以下内容是为了保证英文原意，搜集的资料：
When a PAgP mode of auto or desirable is configured on a port, you also have the option of configuring either of the following operational parameters:An EtherChannel bundle does not form, until bidirectional connectivity has been confirmed. This parameter means that ports in the EtherChannel bundle must receive data, as well as be able to transmit data, in order for the bundle to form. Non-silent is default on Catalyst 5000 fiber-based FastEthernet and fiber-based gigabit Ethernet ports. This mode protects against unidirectional failures, where one of the transmit or receive links may fail. These failures are common on fiber-based connections and can cause bridging loops.
Silent—
An EtherChannel bundle forms, even if data has not been received from the remote device. This mode is the default mode of operation on all Catalyst 4000, 6000, and Cisco IOS-based switch ports, as well as on Catalyst 5000 copper ports. For unidirectional failures on Cisco IOS-based Catalyst ports, Catalyst 4000 ports, and Catalyst 6000 ports, other protocols, such as unidirectional link detection (UDLD), which detect these failures much more quickly than non-silent PAgP operation, are used to protect against unidirectional failures.
Cisco recommends that you do not modify the default silent or non-silent mode of operation.
If i configure pagp auto silent mode, I am telling my switch just form etherchannel when prompted by other switch on the other end. Basically We are telling switch not to be bothered about verifying bi directional communication.
If we configure pagp auto non silent mode, we are telling the switch first verify if bi direction communication exists, if yes then form etherchannel when prompted by other switch on the other end.
The silent submode listens for any PAgP packets from the far end. If none is received, silent submode assumes that a channel should be built anyway
If you expect a PAgP-capable switch to be on the far end,you should add the " Non-silent " key word to the desirable or auto mode. This requires each port to receive PAgP packets before adding them to a channel"
