Hi All, For my issue, first thanks to ALL, I have some idea of it. Also Thank Peter for his kind remind, I would become one good guy in this list. Most mentioned MTU, but how I assure that the problem is just MTU, how I debug it? Here is my bridge configuration: Internet | | Gateway | | eth0 Ethernet Bridge | eth1 | H u b ( one normal hub or switch , no VLAN settings) | \ | \ D-Link 802.1Q VLAN Switches (their uplink port-port 1 connected to the upper hub are tagged, those ports connected with PCs are untagged). Bridge configuration: Linux 2.4.26 ( kernel built in bridge function) Eth0 RTL8139 driver Eth1 Intel e100 NIC with eepro100 driver With VLAN tag, I met the hotmail login error, if without VLAN tag, all are OK! Peter and Ben suggested me use intel NICs, I have one intel e100 NIC and e1000 NIC, e1000 NIC is OK, but I cannt use the e100 card with the e100 driver( from both Linux 2.4.26 and Intel site e100-3.2.3), so I only use eepro100 driver. How I can use the e100 with e100 driver? Can I use e100 and e1000 together( use them as eth0,1)? Any one can help me? Thanks! Kingz