Ways To Protect Your Network

Here are three free tricks to increase your network's security:-

1. Use OpenDNS

Use OpenDNS Internet traffic gets routed through IP addresses; the text you type as a URL only sits on top of those numbers. Normally, when you type pcworld.com, it gets referenced in a domain name server directory, which then routes you to the actual IP address. But what happens if that structure is compromised and an attacker can send your request to a different IP address?

Domain name servers and operating systems were eventually patched to protect against this attack. But the OpenDNS server already anticipated the problem and is quick to react to threats. Use it instead of relying on your ISP's DNS servers.

On the client side, you can open the Network Connections Control Panel. Right-click the active connection, and pick Properties. Select Internet Protocol (TCP/IP), and click Properties. Click the radio button to Use the following DNS server addresses and enter 208.67.222.222 and 208.67.220.220.

Or you can enable it on your router, sending DHCP clients these details without additional intervention. The specific process varies, but you'll essentially log in and enter those IP addresses in the NAT area.

2. Update Your Router Firmware

Psyb0t is a worm that was written to attack router hardware directly, embedding itself inside. It simply guesses the login and password for a range of routers, starting with the defaults. At the very least, you should be using a strong password, especially since many low-end routers don't let you change the login ID.

Just like your operating system, hardware companies typically patch routers over time, especially when security flaws are discovered. Look up your specific model and see if there's a firmware update. If so, download, and apply the revision; it'll likely protect you from many attacks.

3. Disable Remote Administration

In addition to updating your router firmware and giving it a strong password, you can close another door by disabling remote administration. This option is often off by default, but check your router's settings to tell for sure.

With remote administration on, someone can log in from offsite. They'll typically need a valid password, although this access presents another weak point in your defenses.

If you need to administrate the network remotely, set up a secure connection to a VPN gateway at your network, instead of connecting in that open method.

Source: .pcworld.com

DHCP Server Security

Although DHCP servers are critical to the operation of most enterprise networks, DHCP server security is often one of the most overlooked areas of network security. One reason for this might be the simplicity of how DHCP works: DHCP clients broadcast discovery messages (DHCPDISCOVER) containing their MAC addresses and DHCP servers respond by offering (DHCPOFFER) to lease an IP address and other TCP/IP settings that the client can use to communicate on the network. The client responds (DHCPREQUEST) to the first lease offer it receives and the server acknowledges (DHCPACK) the request and marks the address as leased in its DHCP database. That's all there is to it—who needs to worry about security?

Attacking DHCP

Unfortunately it's the very simplicity of DHCP that's actually the problem as far as security goes. No authentication or authorization takes place during an exchange between a DHCP server and DCHP client, so the server has no way of knowing if the client requesting the address is a legitimate client on the network, and the client has no way of knowing if the server that assigned the address is a legitimate DHCP server. The possibility of rogue clients and servers on your network can create all kinds of problems.

For example, a rogue DHCP server could provide legitimate clients with bogus TCP/IP information that prevents the clients from communicating on the network. A denial of service (DoS) condition then results, and users are unable to connect to network resources to perform their work. Setting up a rogue DHCP server could be as simple as conducting a social engineering attack to gain physical access to your network and plugging in a laptop configured as a DHCP server.

Another scenario might involve an attacker compromising a client computer on your network and installing software that repeatedly requests new IP addresses using spoofed MAC addresses until the entire pool of addresses in your DHCP server's scope is leased. When this happens, legitimate clients that boot onto the network can't acquire an address and again users are unable to access the network and can't do their work.

A more sinister result happens when an attacker breaches network security and gains control of your own DHCP servers. At that point the attacker might proceed to modify the DHCP server to assign clients an incorrect subnet setting and thus create another DoS condition. Or they might modify the server to assign clients incorrect DNS settings and redirect clients to rogue or hijacked DNS servers, which could then redirect clients to hostile websites where they unknowingly download a trojan.

Worse yet, if you're running your DHCP server on a domain controller then an attacker who compromises your DHCP server gains access to your accounts database and can cause all sorts of further problems. The result is usually your worst nightmare. Fortunately, there are some measures you can take to protect your DHCP servers and avoid many of these scenarios, provided you're also following all the usual best practices for securing Windows-based networks. Let's look at some specific threats to DHCP on your network and the countermeasures you can take to mitigate these different threats.

Threats and Countermeasures

On the face of it, the requirement that Windows 2000 and Windows Server 2003 DHCP servers be authorized in Active Directory before they can start leasing addresses to requesting clients seems to mitigate the threat of rogue DHCP servers on your network. Authorization means that when a Windows 2000 or Windows Server 2003 DHCP server boots onto an Active Directory network it first contacts a domain controller to check if its own IP address is found on the list of authorized DHCP servers maintained by the domain controller. If the DHCP server determines that it is authorized to lease addresses to clients, it begins to do so. If it's not authorized, Windows shuts down the DHCP Server service on the machine so it won't be able to lease addresses.

The real benefit of this is to protect your network against legitimate DHCP servers that are badly configured, though it has the added side effect of guarding against accidental or rogue DHCP servers running Windows 2000 or Windows Server 2003. What happens though if an attacker compromises your network with a rogue DHCP server not running Windows 2000 or Windows Server 2003? In this case authorization won't help because non-Microsoft DHCP servers may not respond the same way as Microsoft ones to the DHCPINFORM messages Windows uses to check if DHCP servers are authorized.

Rogue clients is another problem entirely though, as DHCP is designed to make it easy for clients to obtain IP addresses so they can participate on a network. The obvious way of dealing with the problem of rogue clients would seem at first to be DHCP reservation, though on large networks this entails considerable administrative overhead. A reservation is a predefined setting that maps a MAC address to an IP address so that only a client with a particular MAC address can lease the IP address associated with that reservation. If security is critical an administrator could create reservations for each and every client machine on the network, and if unreserved IP addresses still remain in the DHCP server's cope then these could be reserved using invalid or non-existing MAC addresses. Then when a rogue client tries to boot on the network the result is that the DHCP server has no free addresses to lease and the client can't connect.

If only it were that simple. While this approach might foil a casual attack, sophisticated attackers have ways for circumventing DHCP reservations. The simplest approach is for the attacker to run a program that listens for DHCPDISCOVER broadcasts from clients and harvests their MAC addresses. Then when a legitimate client shuts down the rogue client can reconfigure its MAC address to match that of the legitimate client and hijack the legitimate client's lease or try to disrupt communications for the client. Considering this, security-conscious administrators might consider dropping DHCP entirely in favor of static addressing, but what's to stop an attacker who has physical access to your network from assigning a static address to their own machine and joining the network?

Via:windowsecurity.com/articles/DHCP-Security-Part1.html

Install a Windows 2003 DNS server

Every network needs a DNS (domain name service) server, right? Windows comes with a DNS server, but it isn’t installed by default. This will tell you how to install a DNS server on a Windows 2003 server.

As an administrator on the system, click Start -> Control Panel -> Add or Remove Programs -> Add/Remove Windows Components.

In the window that opens, click on the Networking Services line (careful not to uncheck the box to the left) and click Details.

Find the line for Domain Name System (DNS), click the checkbox on its left, and Click OK. Click Next.

If Windows asks for a CD-ROM, do as it requests. When it is done, click Finish and you’ll have your very own DNS server.

Source:tech-recipes.com