Securing Your OSPF Network

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Additional Resources on Network Security

Now that you know security should be a serious part of your network at all levels, and you know some of the Golden Rules of designing a secure network, you might need some additional information regarding the bane of “cyber thieves”—“cyber cops.” An article entitled “cyber cops” in the March 10, 1997 issue of Forbes Magazine discussed how a Bill Gates-like college student decided the best way to stop cyber thieves was to show companies where their security holes were. A completely logical move, this resulted in a new company called Internet Security Systems (ISS) whose premise is to stage a break-in with their software and then help plug the holes. If you are interested in finding out more and using their evaluation software, you can check out their home page at, or you can reach them at 1 (800) 776-2362.

Securing Your OSPF Network

There are many ways to secure your network. The sections that follow discuss the easiest and most basic ways to do this. Controlling access to network equipment is the simplest. There are many levels of security, although understanding how to encrypt data and use OSPF authentication within your network should become familiar to you as well.

Controlling Access to Network Equipment

It is important to control access to all of your network equipment. Most equipment manufacturers now design their equipment with multiple levels of passwords, typically read and then read/write. This is probably the easiest and most basic step in securing your network.

This section will discuss some of the techniques and considerations you must take regarding Cisco router access and the operation of their passwords. You can control access to the router using the following methods:

  Console port access
  Telnet access (non-privileged & privileged)
  Terminal Access Controller Access Control System (TACACS)
  Simple Network Management Protocol (SNMP) access
  Controlling access to servers that contain configuration files
  Privilege level security

You can secure the first three of these methods by employing features within the router software. For each method, you can permit nonprivileged access and privileged access for a user (or group of users). Nonprivileged access allows users to monitor the router but not to configure the router. Privileged access enables the user to fully configure the router.

For console port and Telnet access, you can set up two types of passwords. The first type of password, the login password, allows the user nonprivileged access to the router. After accessing the router, the user can enter privileged mode by entering the enable command and the proper password. Privileged mode provides the user with full configuration capabilities.

SNMP access allows you to set up different SNMP community strings for both nonprivileged and privileged access. Nonprivileged access allows users on a host to send the router SNMP get-request and SNMP get-next-request messages. These messages are used for gathering statistics from the router. Privileged access allows users on a host to send the router SNMP set-request messages in order to make changes to the router’s configurations and operational state.

Increasing SNMP Security

It is generally understood and agreed upon that in the networking arena, SNMP is not as secure as it can be. In networks where security is extremely important, you can also implement an access list on SNMP to limit who can access the device in question via SNMP. This can be accomplished as shown in the example that follows.

This example permits the host IP addresses of and to access SNMP on the device. You do this by adding the access-list number on the end of the snmp-server community command.

    access-list 1 permit    access-list 1 permit    snmp-server community cisco5 1 

Console Port Access

A console is a terminal (PC) attached directly to the router via the console port. Security is applied to the console by asking users to authenticate themselves via passwords. By default, there are no passwords associated with console access.

Telnet: Nonprivileged Mode Password (VTY)

Each Telnet port on the router is known as a virtual terminal. There is a maximum of five virtual terminal (VTY) ports on the router, allowing five concurrent Telnet sessions. (The communication server provides more VTY ports.) On the router, the virtual terminal ports are numbered 0 through 4. You can set up nonprivileged password for Telnet access via the virtual terminal ports with the following configuration commands. You configure a password for nonprivileged mode (also known as VTY) by entering the following commands in the router’s configuration file. Remember passwords are case sensitive. In the following example, the password is ospf4U:

    line console 0    login    password ospf4U 

When you log in to the router, the router login prompt is provided:

    User Access Verification    Password: 

You must enter the password ospf4U to gain nonprivileged access to the router. The router response is as follows:


Nonprivileged mode is signified on the router by the > prompt. At this point, you can enter a variety of commands to view statistics on the router, but you cannot change the configuration of the router.

When considering what password format to use—all letters or numbers—it is best to make your passwords an alphanumeric combination with at least one capital letter. Remember that not all cyber thieves are outside your network, and this makes your passwords tougher to crack or guess. For example, the password ospf4U combines all of these suggestions!

Telnet: Privileged Mode Password (enable or exec)

Configure a password for privileged mode—enable or exec—by entering the following commands in the router’s configuration file. In the following example, the password is MCI-good:

    enable-password MCI-good 

To access privileged mode, enter the following command:

    OSPF_Router> enable    Password: 

Enter the password MCI-good to gain privileged access to the router. The router responds as follows:


Privileged mode is signified by the # prompt. In privileged mode (also known as enable mode), you can enter all commands to view statistics and configure the router.

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OSPF Network Design Solutions
OSPF Network Design Solutions
ISBN: 1578700469
EAN: 2147483647
Year: 1998
Pages: 200
Authors: Tom Thomas

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