今天在一个国外站点上看到这么一篇文章。作者介绍说，当你删除Cisco Catalyst交换机的startup-config配置文件之后，再reload交换机，你会发现交换机上的vlan信息仍然存在，并没有被删除。
      我用Packet Tracer 5.0亲自做了下实验假设有三个用户自建vlan 10/20/30，结果如下：
AS01#show vlan brief
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Fa0/4, Fa0/5, Fa0/6, Fa0/7
                                                Fa0/8, Fa0/9, Fa0/10, Fa0/11
                                                Fa0/12, Fa0/13, Fa0/14, Fa0/15
                                                Fa0/16, Fa0/17, Fa0/18, Fa0/19
                                                Fa0/20, Fa0/21, Fa0/22, Fa0/23
                                                Fa0/24, Gig1/2
10   dianjixi                         active    Fa0/1
20   caihuaxi                         active    Fa0/2
30   zihuanxi                         active    Fa0/3
100  admin                            active   
1002 fddi-default                     active   
1003 token-ring-default               active   
1004 fddinet-default                  active   
1005 trnet-default                    active   
AS01#erase startup-config （PS:这里用write erase命令效果一样！）
Erasing the nvram filesystem will remove all configuration files! Continue? [confirm]
[OK]
Erase of nvram: complete
%SYS-7-NV_BLOCK_INIT: Initialized the geometry of nvram
AS01#reload
Proceed with reload? [confirm]
%SYS-5-RELOAD: Reload requested by console. Reload Reason: Reload Command.
Switch>en
Switch#show vlan brief
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
                                                Fa0/5, Fa0/6, Fa0/7, Fa0/8
                                                Fa0/9, Fa0/10, Fa0/11, Fa0/12
                                                Fa0/13, Fa0/14, Fa0/15, Fa0/16
                                                Fa0/17, Fa0/18, Fa0/19, Fa0/20
                                                Fa0/21, Fa0/22, Fa0/23, Fa0/24
                                                Gig1/2
10   dianjixi                         active   
20   caihuaxi                         active   
30   zihuanxi                         active   
100  admin                            active   
1002 fddi-default                     active   
1003 token-ring-default               active   
1004 fddinet-default                  active   
1005 trnet-default                    active 
      不过，startup-config文件删除，没有任何端口加入vlan，因此对于vlan 10/20/30没有相关端口信息。
      但是，从以上例子中，可以清楚地看到之前创建并激活的vlan并没有随startup-config的删除而删除。这是为什么呢？文章作者解释，自建的vlan信息实际上保存在交换机Flash的vlan.dat文件内，该文件不会在删除startup-config的时候被删除，也不会在reload之后清空内容或被删除。以致当重启交换机后，仍然可以从该文件中读取之前保存的vlan信息。该文件需要被手工删除。
      这里还需要注意的是，删除该文件时，需要确认两遍，提示是否删除文件时，无需输入y，直接按回车即可。如果你输入y，则相当于告诉系统你要删除的是名为y的文件，删除会失败。如下所示：
Switch#delete vlan.dat
Delete filename [vlan.dat]?y
Delete flash:/y? [confirm]
%Error deleting flash:/y (No such file or directory)
      正确的做法就是：
Switch#delete vlan.dat
Delete filename [vlan.dat]?
Delete flash:/vlan.dat? [confirm]
      好了，现在重启，之后再来show一把：
Switch#sh vlan b
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
                                                Fa0/5, Fa0/6, Fa0/7, Fa0/8
                                                Fa0/9, Fa0/10, Fa0/11, Fa0/12
                                                Fa0/13, Fa0/14, Fa0/15, Fa0/16
                                                Fa0/17, Fa0/18, Fa0/19, Fa0/20
                                                Fa0/21, Fa0/22, Fa0/23, Fa0/24
                                                Gig1/2
1002 fddi-default                     active   
1003 token-ring-default               active   
1004 fddinet-default                  active   
1005 trnet-default                    active  
      此时，vlan 10/20/30才真正被删除了。老实说，关于这个问题，本人以前也从来没有考虑过，注意细小的地方，往往会帮助你更多地了解设备，希望本文对大家的日常工作以及备考思科认证有所帮助。