“Hurry up and deploy the gear. We have a deadline. Just get it done. We’ll go back later to lock it down.” Sound familiar? For years now, it’s been commonplace for network engineers to do just this. Except, someone rarely goes back to “lock it down”. There are countless ways to improve network security, but today we’ll focus on the low-hanging fruit by providing you with ten simple practices.
10 Simple Ways to Boost Network Security
Always lock rooms with sensitive network equipment. If an unauthorized person can walk into your communication closets, he/she can wreak serious havoc. A person with malicious intent can reset administrative passwords, gain full privileges, create backdoors, and so much more. Even someone without malicious intent can cause major problems. What happens if Jimmy the janitor decides to sweep and accidentally unplugs a distribution switch or two? Uh oh.
2. Update, update, update
Keep your network device software
A list of Cisco product updates can be found here: https://www.cisco.com/c/en/us/support/index.html
3. Encrypt your passwords
Everyone knows that passwords are the keys to the kingdom. Some Cisco devices, specifically IOS-based routers and switches, do not encrypt all types of passwords by default. Prying eyes may see this information and use it for malicious purposes. Enable password encryption by entering the “service password-encryption” command in global configuration mode[i].
- Quick Tip #1: When configuring enable passwords, use “enable secret’” instead of “enable password”’, as the latter uses a very weak form of encryption and is simple to crack.
- Quick Tip #2: When creating local user accounts, never use type 7 passwords. These are considered
unsecure. There are countless tools available to decrypt these passwords very quickly.
4. Use SSH
In the old days, telnet was used as the standard to configure devices across the network. Unfortunately, telnet transmits everything in plain text, so anyone can read it. This includes usernames, passwords, configurations, and anything else sent through a telnet window.
Using telnet makes it easier for attackers to obtain sensitive information. Surprisingly, many organizations still use telnet for remote configuration of their switches, routers, and even firewalls. Secure Shell (SSH) encrypts this data across the network. It’s best to disable telnet and enable SSH where possible.
On an IOS-based Cisco router or switch, these quick commands should get you where you need to be:
Switch(config)# hostname <enter hostname>
Switch(config)# crypto key generate
Telnet is bad for managing network devices but is still good for some things. Telnet to towel.blinkenlights.nl to watch an ASCII version of Star Wars!
Your organization doesn’t want an angry employee, student, or visitor attempting to authenticate to your network gear. These devices should only be accessed by the appropriate IT staff. For Cisco routers and switches, this can be locked down by creating an
Below is an example
Switch(config)# access-list 10 permit 10.10.10.0 0.0.0.255
Switch(config-line)# access-class 10 in
6. Use SNMP wisely
SNMP is a necessity when it comes to monitoring your network environment. However, most organizations don’t configure SNMP in a secure manner. This data can contain network configurations, device versions, and unencrypted passwords (see #3 on this list). A device can also be configured via SNMP. An attacker would have a
Here are some tips on how to use SNMP wisely:
- Use SNMPv3 whenever possible. SNMPv3 allows for both authentication and encryption (privacy) which is a tremendous improvement over the older versions.
- Use an SNMP access-control List (ACL). This limits the IP addresses which can access the device via SNMP.
- If SNMPv2c must be used, don’t use simple (or default) read and read-write strings. Change the strings to be consistent with your
7. Disable unnecessary services
Network devices have a slew of services running in the background. Many are necessary, but not all. These unnecessary services can waste additional resources, but more importantly, can increase the attack surface of the device. Below is a list of IOS-based services you should disable, unless absolutely required[iii]:
- TCP & UDP Small Servers - Rarely used built-in services used for diagnostics relating to echo,
chargen, discard, daytime commands. Disable by using the commands below:
Device(Config)# no service
Device(Config)# no service
- IP Finger - Rarely used finger service allowing remote users to show the equivalent of the show users command. Disable by using the command below:
ipfinger (or no service finger)
- IP BOOTP Server - Rarely used bootstrap protocol. Disable by using the command below:
ip dhcp bootpignore if the DHCP service is used)
- MOP - Rarely used maintenance operation protocol. Disable by using the command below:
Device(Config)# no mop enabled
- IP Domain Lookup - Rarely used, and sometimes annoying, DNS resolution services. Disable by using the command below:
- Service Pad - Rarely used packet assembler/disassembler service (used for x.25 networks). Disable by using the command below:
Device(Config)# no service pad
- HTTP/HTTP Server - Rarely used internal web-server. If not being used, this should be disabled. Disable by using the commands below:
- Service Config - Rarely used service for retrieving configurations from the network instead of on local storage. Disable by using the command below:
Device(Config)# no service config
- Quick Tip #1: Cisco has started disabling some of these services by default in recent IOS versions. When in doubt, try and disable them anyway.
- Quick Tip #2: NX-OS devices are a bit smarter and require
useof the ‘feature’ command to enable certain services and features.
8. VLAN 1.
Depending on your environment this one might not fall into the simple category. While there are various solutions to mitigate the risks and concerns with using VLAN 1, it’s usually simpler to avoid using it at all.
Here are a few reasons not to use it:
- By default, all Cisco
switchportsare assigned to VLAN
This can be a security risk if unused
switchportsaren’t shut down or changed to a different VLAN.
- VLAN 1 is the default native VLAN on trunks
Unless the native VLAN is changed to an unused VLAN, this is another security risk which can be used in a VLAN Hopping attack[iv].
- VLAN 1 is used for control related traffic
Various protocols including VTP, CDP, and PAgP use this VLAN which traverse a trunk even if pruned. Using VLAN 1 for endpoints can be sub-optimal.
9. Don’t forget to log
Device logs can be extremely helpful, especially when there is a security
Here is a list of best practices for logging:
- Ensure logging is configured for the proper logging level
On Cisco routers, switches, firewalls – this is usually level 6 (Informational)
- Both time and timestamps should be accurate
The device should be using a valid NTP server and the time zone should be correct
- Use an external logging server
Open-source (or minimal cost)
syslogsoftware is widely available
- Log to the device buffer
Logging to the device’s buffer can make troubleshooting easier
10. Backup your configs
Server teams are pros when it comes to backups. Unfortunately, that’s not always the case on the network side of the house. Routers, switches, and firewalls need some backup loving too. Configurations can be rebuilt without backups; however, it will be much more painful and
For smaller organizations, a simple copy and paste of the configuration files will work just fine. Larger organizations may want to look at automated tools which do this on a regular basis.
A truly secure network environment is made up of many layers. The recommendations above address only a small handful. If this article peaks your interest in learning more about your own network security, feel free to reach out to our Security Team. We’ll be glad to perform a complete assessment and provide intuitive and informative results.
About the Author
Dave Barus has been working in the IT field for over 15 years with extensive experience in networking and security. He spent many years working overseas assisting the U.S. Military with the design, configuration, and management of enterprise networks in the Middle East. Since returning to the U.S. he has moved into the VAR space specializing in the design & implementation of various technologies for organizations throughout the world. Dave now works for Internetwork Engineering as a Solutions Engineer helping customers find the right technology solution for their business.