Alcatel Unleashed

You don't need qos here.
There is no magic like vtp on cisco, so you have to create each and all vlans on all switches and tag them to the trunk port
vlan 10 802.1Q 1/1
vlan 11 802.1Q 1/1
vlan 12 802.1Q 1/1
vlan 20 802.1Q 1/1

Do that on both sides.

Depends on how you want to communicate. Are the VLANs communicating without firewall (e.g. from vlan 17 to vlan 19?) Should traffic be firewalled between these vlans? How does the firewall want to communicate with the vlans? What is the source IP of the traffic comming from firewall? If your vlans a...

According to my manual it should be in 6900 as well, was introduced with 7.3.4 and extended in 8.2.1

loopback-detection enable
loopback-detection port 1/1/1 enable
loopback-detection port 1/1/1-8 enable

USB recovery depends on Uboot/miniboot version because it was introduced as far as i know with 6.3.1 or 6.3.4(?) (or something similar). If you have such version installed it should be doable. have a fat16 USB that is detected by alcatel switches (check with another switch "usb enable" sho...

SLB is Serverload balancing and something completly different to load balancing internet traffic. Also SLB will not compete against commercial load balancers that offer way more features. on the otherhand: slb comes for free, so if you have need for that it may be worth to invest some time and see w...

my 0.02$: You could theoretically try to work with QOS Rules and PBR, but frankly thats not what a L3 Switch is made for. Even a expensive firewall from Ci*co had/has issues when it comes to loadbalanceing traffic, I don't think you wil be happy with a 6860 doing it. I heared good comments about UBN...

Yes that is perfectly fine.
You can use the 10G Ports only in the U24X of course.
(You can also stack with all flavors of 6450 (6450-48, 6450-P24.. ..)
You need the XNI-U2 modules for stacking (back of the switch) and DAC Cables

I have no idea.. open a SR

The Switch is EoL, so it will be hard to find a good solution. There has bee a software upgrade to 6.4.4 (are you sure you run a 6.4.6 on a 6850 (non E)? PR 199440 Build: 6.4.4.721.R01 Summary: Vulnerability in SSLv3 (POODLE / CVE -2014- 3566) Explanation: Disable SSLv3 to mitigate POODLE attack Sam...

qos log is for qos policys with logging enabled

show log swlog shows you (on a reasonable new software) the logs of the device.