It's quite a easy thing to config vlan trunking btw Cisco catalyst switches. But as someone has mentioned on this forum, I'm now amazing in configuring trunk to synchronous multi vlan between a Cat3524 and a 3Com 3800 switch.I'v configured a trunk port on Cat3524 as usual in connecting with other Catalyst switches, but set encapsulation to be "dot1q", i.e. ieee 802.1Q. But on the other end of the link, 3Com's 3800 has no concept of "vtp domain" and create vlan by defining a vlan name like "Eng_flr3". From 3Com's simple manual, it seems there is a feature named "Tag Number" to configure on a port to transfer multi-vlan traffic just like Cisco' trunk port. And there's a vlan number set by 3800 similar as vlan id on Cat3524.I've tried to config some same vlans on both switches, but PCs can not ping others on another switch but in same vlan. On Cat3524, other vlans' information can not be learnt. Someone in former conversation on this forum said 3Com's vlan "default", which has a Tag id of 127 and a vlan id of 1 in my case, is a native vlan, and the default vlan number on Cat3524 should be changed to other local vlan. I've tried, but with no effect, or maybe there's still some critical config should be set on 3Com 3800?I'll be really very thankful if anyone has experience on this problem could give me some advice.