Best practice for "uplink" ?

Please post all the configs. 

This is basic stuff and works well with these switches.  Since you see STP messages you most likely have an error in your config file or youi cabled it incorrectly.  

Thansk for your reply,

Well, where i can "find" the configs ? or.. how to post it ?

ok, something really weird..

I lost the configuration on the 5448, when i set the LAG I also set the date time  and other informations. Now... There's nothing !

here's the configurations

PowerConnect 5424 :
console# show running-config
interface port-channel 1
description UpLink1
flowcontrol auto
exit
interface port-channel 2
description Uplink2
flowcontrol auto
exit
interface ethernet g3
flowcontrol auto
exit
bridge aging-time 360
voice vlan oui-table add 0001e3 Siemens_AG_phone________
voice vlan oui-table add 00036b Cisco_phone_____________
voice vlan oui-table add 00096e Avaya___________________
voice vlan oui-table add 000fe2 H3C_Aolynk______________
voice vlan oui-table add 0060b9 Philips_and_NEC_AG_phone
voice vlan oui-table add 00d01e Pingtel_phone___________
voice vlan oui-table add 00e075 Polycom/Veritel_phone___
voice vlan oui-table add 00e0bb 3Com_phone______________
port-channel load-balance layer-2-3
interface range ethernet g(1,3,5,7)
channel-group 1 mode on
exit
interface range ethernet g(13,15,17,19)
channel-group 2 mode on
exit
iscsi target port 860 address 0.0.0.0
iscsi target port 3260 address 0.0.0.0
interface vlan 1
ip address 10.0.5.1 255.0.0.0
exit
arp timeout 86400
ip default-gateway 10.0.0.1
aaa authentication enable default line
aaa authentication login default line
line telnet
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
line ssh
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
line console
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
username Admin password xxxxxx8cf19ba46a5de1f5d725769ad6 level 15 en
crypted
snmp-server community Dell_Network_Manager rw view DefaultSuper
clock timezone 1
clock summer-time recurring eu
ip domain-name xxxxx.local
ip name-server  10.0.10.1 10.0.10.2

Default settings:
Service tag:

SW version 1.0.0.31 (date  31-Oct-2007 time  10:32:13)

Gigabit Ethernet Ports
=============================
no shutdown
speed 1000
duplex full
negotiation
flow-control off
mdix auto
no back-pressure

interface vlan 1
interface port-channel 1 - 8

spanning-tree
spanning-tree mode STP

qos basic
console#

PowerConnect 5324 :
console# show running-config
interface port-channel 1
description UpLink1
flowcontrol auto
back-pressure
exit
bridge aging-time 360
interface ethernet g1
channel-group 1 mode on
exit
interface ethernet g2
channel-group 1 mode on
exit
interface ethernet g3
channel-group 1 mode on
exit
interface ethernet g4
channel-group 1 mode on
exit
interface vlan 1
ip address 10.0.5.0 255.0.0.0
exit
arp timeout 86400
ip default-gateway 10.0.0.1
aaa authentication enable default line
aaa authentication login default line
line telnet
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
line ssh
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
line console
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
username Admin password xxxxxxcf19ba46a5de1f5d725769ad6 level 15 en
crypted
clock summer-time recurring eu
ip domain-name xxxxxx.local
ip name-server  10.0.10.1 10.0.10.2
console#

PowerConnect 5448 :
console# show running-config
voice vlan oui-table add 0001e3 Siemens_AG_phone________
voice vlan oui-table add 00036b Cisco_phone_____________
voice vlan oui-table add 00096e Avaya___________________
voice vlan oui-table add 000fe2 H3C_Aolynk______________
voice vlan oui-table add 0060b9 Philips_and_NEC_AG_phone
voice vlan oui-table add 00d01e Pingtel_phone___________
voice vlan oui-table add 00e075 Polycom/Veritel_phone___
voice vlan oui-table add 00e0bb 3Com_phone______________
iscsi target port 860 address 0.0.0.0
iscsi target port 3260 address 0.0.0.0
interface vlan 1
ip address 10.0.5.2 255.0.0.0
exit
ip default-gateway 10.0.0.1
aaa authentication enable default line
aaa authentication login default line
line telnet
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
line ssh
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
line console
password xxxxxx8cf19ba46a5de1f5d725769ad6 encrypted
exit
username Admin password xxxxxx8cf19ba46a5de1f5d725769ad6 level 15 en
crypted
snmp-server community Dell_Network_Manager rw view DefaultSuper

Default settings:
Service tag:

SW version 1.0.0.31 (date  31-Oct-2007 time  10:32:13)

Gigabit Ethernet Ports
=============================
no shutdown
speed 1000
duplex full
negotiation
flow-control off
mdix auto
no back-pressure

interface vlan 1
interface port-channel 1 - 8

spanning-tree
spanning-tree mode STP

qos basic
console#

<ADMIN NOTE:Service Tag Removed Per Privacy Policy>

console> enable

console# show running-config

Do this on all 3 switches and post the output  here.

You do not have a port-channel set up on the 5448.   Set it up and let us know how it works. 

Yes, that's what i saw when i exported the configuration.. but i'm sure that i set it up ! is it possible that the switch make a "reset" by itself ??

I'll make the test today and keep you informed, thanks a lot

In fact it works perfectly, i think i made a mistake with the port numbers, on the 5324 the LAG configuration differs from the other ones.. i also saved the running config. into the starting configuration one the 3 switches, by this way i should be sure the setup won't be lost again.

Thanks a lot, again !

Patrick