在添加cisco Sw port-channel 中的vlan时的注意点(未测试)
在给CISCO Switch port-channel追加vlan的时候一定要注意操作的顺序结论：在给port-channel追加vlan的时候必须要现在逻辑端口即port-channel里面追加vlan ，然后才是在相应的port-channel所属的物理端口上追加新vlan。如果先在物理端口里添加vlan然后再在逻辑端口即port-channel里面追加vlan ，则会使prot-channel工作不正常，导致原有的vlan通信也被阻断，影响堪大。
◆ 网络构成
如下图交换机SW1，SW2的Port22和Port23组成port-channel。
并且port-channel中已经有vlan10的数据正常通过。
本次在该Po1加入vlan20，使vlan20的流量也通过port-channel实现均分
--------Po 1 --------
|SW1 |Gi 0/22|SW2 |
| |Gi 0/23| |
-------- --------
vlan10(+vlan20)
◆ 正确的操作过程
操作的正确顺序是(1)→(2)→(3)，其他非相关配置可以忽略。
(1) 配置vlan端口，（该处操作与本案研究无关）
int vlan20
description to VLAN_20
ip address *.*.*.1 255.255.255.240
no ip redirects
no ip proxy-arp
standby ip *.*.*.3
standby priority 255
standby preempt
standby track GigabitEthernet0/28 200
shut
(2) 在逻辑端口Po1里添加vlan20 ←该步骤必须先执行
interface Port-channel1
description HOGE_SW1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 10,20
switchport mode trunk
(3) 在物理端口里面添加vlan20 ←该步骤后执行
interface GigabitEthernet0/22
description HOGE_SW1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 10,20
switchport mode trunk
speed 1000
duplex full
no cdp enable
channel-group 1 mode desirable
interface GigabitEthernet0/23
description HOGE_SW2
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 10,20
switchport mode trunk
speed 1000
duplex full
no cdp enable
channel-group 1 mode desirable
(4) 确认Po1状态正常
#sh etherchannel summary
Flags:D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 2
Number of aggregators: 2
GroupPort-channelProtocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SU) LACP Gi0/22(P) Gi0/23(P) ←显示状态正常
◆ 不正确的操作方法
上面的操作顺序如果改为(1)→(3)→(2)的顺序的话，就会导致port-cahnnel失效。
显示log如下
#sh etherchannel summary
Flags:D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 2
Number of aggregators: 2
GroupPort-channelProtocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SD) LACP Gi0/22(s)Gi0/23(s)←显示状态异常
#sh interfacesgi0/22
GigabitEthernet0/22 is up, line protocol is down (suspended)←显示端口协议挂了
#sh interfacesgi0/23
GigabitEthernet0/23 is up, line protocol is down (suspended)←显示端口协议挂了
请各位同学在实际工作中一定注意这个操作顺序。
最后页补充一个知识点：在2960s 交换机里面，这条命令switchport trunk encapsulation dot1q是无法输入的，查看cisco的文档后确认在2960s里面默认就只支持dot1q协议，所以就不再支持switchport trunk encapsulation dot1q的输入了。
from：http://blog.sina.com.cn/s/blog_7f2122c50100vl0n.html
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