ftp,scp可以建立连接，但是不能传输数据

哈尔滨(host1)---上海[FTP1（windows,server-U），FTP2(linux,vsftp)]
host1(wget~)-----FTP1[OK]
host1(wget~)-----FTP2[NO]

故障现象：
[root@haerbing ~]#  wget ftp://ftpuser:ftpuser@shanghaiIP/xen/XenServer-5.6.1-fp1-install-cd.iso
--2012-06-07 03:33:44--  ftp://ftpuser:*password*@shanghaiIP/xen/XenServer-5.6.1-fp1-install-cd.iso
           => `XenServer-5.6.1-fp1-install-cd.iso.3'
Connecting to IP:21... connected.
Logging in as ftpuser ... Logged in!
==> SYST ... done.    ==> PWD ... done.
==> TYPE I ... done.  ==> CWD /xen ... done.
==> SIZE XenServer-5.6.1-fp1-install-cd.iso ... 441192448
==> PASV ... done.    ==> RETR XenServer-5.6.1-fp1-install-cd.iso ... done.
Length: 441192448 (421M)
 0% [                                                                     ] 0           --.-K/s   in 15m 0s


公司网络部的大牛哥找出了原因[哈哈！]

故障原理：
MTU+以太网包头+运营商VPN
1500+18+N
VPN不支持分包?

故障解决方法：
主机的MTU改小一点就可以了传输数据了！
[linux]
#1
ifconfig eth0 mtu 1400
#2
ip link set dev eth0 mtu 1400
#3
vi /etc/sysconfig/network-scripts/ifcfg-eth0
MTU=1400
[windows]
难道windows支持自动缩小MTU?