Trunk between 1800-24g and 1810g-8

[Werner Steinegger]

Hello, in the office are 3 switches: 2 1800-24g (1 J9028A & 1 J9028B) and 1 new 1810g-8
FW of the switches:
1810: (switch c) P1.14
1800: (switch a) PB03.04 & (switch b) PB03.01

We have only 1 vlan, vlan 1
I try to build a trunk between switch a port 21,23 and switch c port 7 and 8

All settings i tried failed and i lose the connection between the two switch.
I build a trunk between switch a port 22 and 24 and switch b port 21 and 23, thios one works fine.

I build up a lot of trunk and vlans on HP Switches 35xx,54xx,28xx etc. but i don't no what is wrong with the settings on the 1810....

Settings of the 1810 look like this port 7,8 member of trk1
trk1 LACP yes, VLAN T

Settings of 1800
port 21,23 member of trunk1
vlan all VLAN 1 (also tried here tagged only with none and vlan 1) also not worked.

What is wrong ??? any ideas are welcome

kind regards
werner