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Cisco IOS Security Configuration Guide, Release 12.2
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About the Cisco IOS Software Documentation
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Using Cisco IOS Software
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Security Overview
- Part 1: Authentication, Authorization, and Accounting (AAA)
- Part 2: Security Server Protocols
- Part 3: Traffic Filtering and Firewalls
- Part 4: IP Security and Encryption
- Part 5: Other Security Features
- Part 6: RADIUS Attributes
- Part 7: Appendixes
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Installation and Configuration for Common Criteria EAL4 Evaluated Cisco IOS IPSec
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Feedback
Table Of Contents
Neighbor Router Authentication: Overview and Guidelines
Benefits of Neighbor Authentication
Protocols That Use Neighbor Authentication
When to Configure Neighbor Authentication
How Neighbor Authentication Works
Finding Neighbor Authentication Configuration Information
Neighbor Router Authentication: Overview and Guidelines
You can prevent your router from receiving fraudulent route updates by configuring neighbor router authentication.
This chapter describes neighbor router authentication as part of a total security plan. It describes what neighbor router authentication is, how it works, and why you should use it to increase your overall network security.
This chapter refers to neighbor router authentication as "neighbor authentication." Neighbor router authentication is also sometimes called "route authentication."
In This Chapter
This chapter describes the following topics:
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About Neighbor Authentication
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About Neighbor Authentication
This section contains the following sections:
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Benefits of Neighbor Authentication
When configured, neighbor authentication occurs whenever routing updates are exchanged between neighbor routers. This authentication ensures that a router receives reliable routing information from a trusted source.
Without neighbor authentication, unauthorized or deliberately malicious routing updates could compromise the security of your network traffic. A security compromise could occur if an unfriendly party diverts or analyzes your network traffic. For example, an unauthorized router could send a fictitious routing update to convince your router to send traffic to an incorrect destination. This diverted traffic could be analyzed to learn confidential information of your organization, or merely used to disrupt your organization's ability to effectively communicate using the network.
Neighbor authentication prevents any such fraudulent route updates from being received by your router.
Protocols That Use Neighbor Authentication
Neighbor authentication can be configured for the following routing protocols:
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When to Configure Neighbor Authentication
You should configure any router for neighbor authentication if that router meets all of these conditions:
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How Neighbor Authentication Works
When neighbor authentication has been configured on a router, the router authenticates the source of each routing update packet that it receives. This is accomplished by the exchange of an authenticating key (sometimes referred to as a password) that is known to both the sending and the receiving router.
There are two types of neighbor authentication used: plain text authentication and Message Digest Algorithm Version 5 (MD5) authentication. Both forms work in the same way, with the exception that MD5 sends a "message digest" instead of the authenticating key itself. The message digest is created using the key and a message, but the key itself is not sent, preventing it from being read while it is being transmitted. Plain text authentication sends the authenticating key itself over the wire.
Note
Caution
This section includes the following sections:
Plain Text Authentication
Each participating neighbor router must share an authenticating key. This key is specified at each router during configuration. Multiple keys can be specified with some protocols; each key must then be identified by a key number.
In general, when a routing update is sent, the following authentication sequence occurs:
Step 1
Step 2
Step 3
These protocols use plain text authentication:
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MD5 Authentication
MD5 authentication works similarly to plain text authentication, except that the key is never sent over the wire. Instead, the router uses the MD5 algorithm to produce a "message digest" of the key (also called a "hash"). The message digest is then sent instead of the key itself. This ensures that nobody can eavesdrop on the line and learn keys during transmission.
These protocols use MD5 authentication:
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Key Management (Key Chains)
You can configure key chains for these IP routing protocols:
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These routing protocols offer the additional function of managing keys by using key chains. When you configure a key chain, you specify a series of keys with lifetimes, and the Cisco IOS software rotates through each of these keys. This decreases the likelihood that keys will be compromised.
Each key definition within the key chain must specify a time interval for which that key will be activated (its "lifetime"). Then, during a given key's lifetime, routing update packets are sent with this activated key. Keys cannot be used during time periods for which they are not activated. Therefore, it is recommended that for a given key chain, key activation times overlap to avoid any period of time for which no key is activated. If a time period occurs during which no key is activated, neighbor authentication cannot occur, and therefore routing updates will fail.
Multiple key chains can be specified.
Note that the router needs to know the time to be able to rotate through keys in synchronization with the other participating routers, so that all routers are using the same key at the same moment. Refer to the Network Time Protocol (NTP) and calendar commands in the "Performing Basic System Management" chapter of the Cisco IOS Configuration Fundamentals Configuration Guide for information about configuring time at your router.
Finding Neighbor Authentication Configuration Information
To find complete configuration information for neighbor authentication, refer to the appropriate section and chapter in the Cisco IOS IP Configuration Guide as listed in Table 29.
To find complete configuration information for key chains, refer to the "Managing Authentication Keys" section in the chapter "Configuring IP Routing Protocol-Independent Features" of the Cisco IOS IP Configuration Guide.
