When repetition occurs is proportionate to any person who can not benefit from the service

Though not exactly what you asked for: you should use NTP and fix the clock on your router, and stop using public IPs for your internal clients. 172.0.0.55 is a public IP address.

thanks fewi for ur fast reply ; i make edit for the post.

After research in the network i found that this problem occurs only with win7 operating system

why win7 cant Accept DHCP normaly like win xp???

why win7 cant Accept DHCP normaly like win xp???

hmm, maybe Win7 doesn't accept illegal (bacause not public) addresses? Try address range out of this:http://www.vicomsoft.com/glossary/ip-addresses/
See if it still happens. If not, you have your answer. If the problem is still there you have to give us more info on the config and network setup to help you out..

this problem happen with me and with all my friends who have mt 750 or 750g
most of them use ips like 192.168.88.1 for network!!
and i foud when i remove netmask 30 the win7 accpt dhcp normaly ,But I need to isolate the devices.


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that’s my config file in attachment:

But I need to isolate the devices.

Giving your dhcp server's network a netmask /30 is not working. It means the network is only 2 IP's big.
What do you mean with "isolate"? Are we talking wireless clients? or wired?
In first cast disable the "forward" option in the wireless, in the wired case set up some good firewall.
One dhcp server can only work in one network. You cannot make it assign IP's in different networks. And every dhcp-client device in the ´one´ network is therefore also reachable by other units.

thank u WirelessRudy for ur fast replay.
when we use sub net mask 30 on xp no client can see other and that is very good protraction for the network, and its work normally in wired network.
when the win7 Spread we found that win7 not accept the dhcp and we must put the ip manually.

If you need to isolate clients, don't use netmask hacks. Just prevent stations from passing traffic to one another, which is very simple to do in wireless networks.

http://wiki.mikrotik.com/wiki/Manual:In ... properties

default-forwarding (yes | no; Default: yes) This is the value of forwarding for clients that do not match any entry in the access-list

Setting default-forwarding on the wireless interface to 'no' means that unless clients are overridden via access-lists they cannot pass traffic between each other directly on the hardware of the wireless interface. Combine that with an IP firewall rule in the 'forward' chain that prevents same network traffic between stations and you've successfully isolated stations from one another. Such an IP firewall rule would look like this: I'd also like to stress again that you should only be using RFC1918 address space (private IP addresses) unless you've been assigned public IPs from your local RIR. 172.0.0.0/24 is NOT a private IP address. You should renumber your network.