Hi my friends! Here is my problem: I have a Switch L3 Dell Power Connect 6248 which has VLANs configured on it. Each VLAN is a LAB. Port 2: vlan2. 172.31.2.x Port3: vlan3. 172.31.3.x I have a DHCP Server Windows Server 2008 connected directly on port 20 of thiw switch and this server has th ip 172.31.0.220. It is also the File Server from students put their files. This server has different scopes from each subnet (each vlan). On the Switch is configured a DHCP Relay pointing to this server (172.31.0.220). The PC's from each lab use DHCP. Everything always working well until the day that they asked me to "close" the vlans on the switch. So i made the following configuration of the ACLs (i made this by web console, not using command line). I made it in: Switching / Network Security / Access Control Lists / Ip Access Control Lists / Rule Configuration/ Permit 172.31.2.0 0.0.0.255 172.31.2.0 0.0.0.255 (with this, pcs in the same lab can watch themselves) Permit 172.31.2.0 0.0.0.255 172.31.0.220 0.0.0.0 (with this, students can see their documents and pcs can get ip from dhcp) Permit 172.31.2.0 0.0.0.255 172.31.255.254 0.0.0.255 (its the ISA server IP. with this, pcs can access Internet) On pratic, the result of this was: pcs can see other pcs on the same vlan and dont see pcs on other labs (its OK); pcs can access internet (its OK); students can see their docs (its OK). The Problem is that it works for a few hours (maybe max 2) and after this, the pcs lost connectivity with the DCHP server (they use DHCP, no static) and they get the generic ip 169.x.x.x and everything stoping working. :( : ( When i configure Static IP on theese PC's everything works fine! :) Anyone can help me to find a solution to this case? I need that eveything works using DHCP an not static ip. Thanks for everything!