There are two philosophies to blocking ports, and which one is appropriate for your network depends on the level of security that you require.
For a high-security network, especially when storing or maintaining confidential data, it is normally recommended to "filter by permission." This is the scheme in which all ports and IP address permissions are blocked, except for what is explicitly required for network functions. For instance, port 80 for web traffic and 110/25 for SMTP can be allowed to come from a dedicated address, while all other ports and addresses can be disabled.
Most networks will enjoy an acceptable level of security by using a "filter by rejection" scheme. When using this filtering policy, ports that are not used by your network and are commonly used for Trojan Horses or reconnaissance can be blocked to increase the security of your network. For instance, blocking ports 139 and 445 (TCP and UDP) will make your network more difficult to enumerate, and blocking port 31337 (TCP and UDP) will make you more secure from Back Orifice.
This should be determined during the network planning phase, when the level of security required is compared to the needs of the network users.
Requires Membership to View
To gain access to this and all member only content, please provide the following information:
By submitting your registration information to SearchNetworkingChannel.com you agree to receive email communications from the TechTarget network of sites, and/or third party content providers that have relationships with TechTarget, based on your topic interests and activity, including updates on new content, event notifications, new site launches and market research surveys. Please verify all information and selections above. You may unsubscribe at any time from one or more of the services you have selected by editing your profile, unsubscribing via email or by contacting us here
- Your use of SearchNetworkingChannel.com is governed by our Terms of Use
- We designed our Privacy Policy to provide you with important disclosures about how we collect and use your registration and other information. We encourage you to read the Privacy Policy, and to use it to help make informed decisions.
- If you reside outside of the United States, by submitting this registration information you consent to having your personal data transferred to and processed in the United States.
Fortifying router security
Introduction
Step 1: Change the default password!
Step 2: Disable IP directed broadcasts
Step 3: Disable HTTP configuration for the router, if possible
Step 4: Block ICMP ping requests
Step 5: Disable IP source routing
Step 6: Determine your packet filtering needs
Step 7: Establish Ingress and Egress address filtering policies
Step 8: Maintain physical security of the router
Step 9: Take the time to review the security logs
About the author
Chris Cox is a network administrator for the United States Army, based in Fort Irwin, California.
This tip originally appeared on SearchNetworking.com.
This was first published in January 2007