3Com 3870 switch Config

Ok call me stupid but I am have great difficulty configuring these switches. I am sure what I want to do is possible but I cant see to get it to work!

I need to run 2 networks through the same switch..... 192.x.x.x and 172.x.x.x these networks need to then run across fibre to another 3870 switch.
now I can send both networks down 1 fibre and everything runs fine... but I want to send each network down a separate fibre using ports 21 and 24 (Gig fibre ports). I have setup Vlans and IP Interface and everything else I can think of but still it does not work with both fibres connected. As soon as i connect the second fibre (and it doesn't matter which is connected) I can no longer get an ip from either server 172 or 192?

Can anyone help as this is making my head spin i have spent so long staring at it!!

Thank you

Since your using 2 uplinks here. You don't need to set them as TRUNK ports any more. Just set both as ACCESS mode each one as part of it's corresponding VLAN, it should work this way.

I can see that option on the new 3Com switches but not on these ones. It seems that I can always get a 192 IP with both fibres connected but not a 172. 192 is also the Primary IP of the switch, I dont know if this has anything to do with it?

I can see that option on the new 3Com switches but not on these ones.

You can't see the option to change the ports to TRUNK / ACCESS modes?, is that what you meant?

yep thats it!

I wonder then how you were able to setup the two VLANs to work on one fibre, since that fibre port needs to be a TRUNK. I'm talking cisco terminology here, so 3Com might have different naming for it.

Ok, this is what I understand from you. You have assigned some ports as VLAN1 and some ports and VLAN2. Then you assigned one port as TRUNK and connected it to the other switch and it worked. Is that what you've done?

Or did you just assign IPs to the hosts some as 192.x.x.x and some 172.x.x.x. and simply connected one of the ports to the other switch and it worked?

Which one is it?