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Neighbor Router Authentication: Overview and Guidelines
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Neighbor Router Authentication: Overview and Guidelines

Table Of Contents

Neighbor Router Authentication: Overview and Guidelines

In This Chapter

About Neighbor Authentication

Benefits of Neighbor Authentication

Protocols That Use Neighbor Authentication

When to Configure Neighbor Authentication

How Neighbor Authentication Works

Plain Text Authentication

MD5 Authentication

Key Management (Key Chains)

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:

About Neighbor Authentication

How Neighbor Authentication Works

Key Management (Key Chains)

Finding Neighbor Authentication Configuration Information

About Neighbor Authentication

This section contains the following subsections:

Benefits of Neighbor Authentication

Protocols That Use Neighbor Authentication

When to Configure Neighbor Authentication

Benefits of Neighbor Authentication

When configured, neighbor authentication occurs whenever neighbor routers exchange routing updates. 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 that traffic. For example, an unauthorized router could send a fictitious routing update to convince your router to send traffic to an incorrect destination. The unfriendly party could analyze the diverted traffic to learn confidential information about your organization or merely use it to disrupt your organization's ability to communicate effectively using the network.

Neighbor authentication prevents your router from receiving any such fraudulent routing updates.

Protocols That Use Neighbor Authentication

You can configure neighbor authentication for the following routing protocols:

Border Gateway Protocol (BGP)

Director Response Protocol (DRP) Server Agent

Intermediate System-to-Intermediate System (IS-IS)

IP Enhanced Interior Gateway Routing Protocol (EIGRP)

Open Shortest Path First (OSPF)

Routing Information Protocol (RIP) version 2

When to Configure Neighbor Authentication

You should configure any router for neighbor authentication that

Uses any of the routing protocols previously mentioned.

Might conceivably receive a false route update.

Might compromise the network if it were to receive a false route update.

Has a neighbor that is already configured for neighbor authentication.

How Neighbor Authentication Works

When you configure a router for neighbor authentication, it authenticates the source of each routing update packet that it receives. The sending router and the receiving router accomplish this by exchanging an authenticating key (sometimes called a password) that is known to both routers.

There are two types of neighbor authentication: plain text and Message Digest Algorithm Version 5 (MD5). Both types work the same way, except that MD5 sends a message digest instead of the authenticating key itself. MD5 creates a message digest by using the key and a message, but the key itself is not sent, which prevents it from being read during transmission. Plain text authentication sends the authenticating key itself over the wire.


Note You should not use plain text authentication as part of your security strategy. You should use it primary to avoid accidental changes to the routing infrastructure. You should use MD5 authentication instead.



Caution As with all keys, passwords, and other security secrets, you must closely guard authenticating keys used in neighbor authentication. This is because the security benefits of this feature rely on the confidentiality of authenticating keys. Also, when performing router management tasks via Simple Network Management Protocol (SNMP), do not ignore the risk associated with sending keys using non-encrypted SNMP.

This section includes the following subsections:

Plain Text Authentication

MD5 Authentication

Plain Text Authentication

Each participating neighbor router must share an authenticating key. You specify this key at each router during configuration. You can specify multiple keys with some protocols (if so, you must identify each by a key number).

In general, when a router sends a routing update, the following authentication sequence occurs:


Step 1 A router sends a routing update with a key and the corresponding key number to the neighbor router. In protocols that can have only one key, the key number is always zero.

Step 2 The receiving (neighbor) router checks the received key against the same key stored in its own memory.

Step 3 If the two keys match, the receiving router accepts the routing update packet. If the two keys do not match, it rejects the routing update packet.

These protocols use plain text authentication:

DRP Server Agent

IS-IS

OSPF

RIP version 2


MD5 Authentication

MD5 authentication works much like plain text authentication, except that MD5 never sends the key over the wire. Instead, the router uses the MD5 algorithm to produce a message digest of the key (also called a hash). The router sends the message digest instead of the key itself, which ensures that no one can eavesdrop on the line and learn keys during transmission.

These protocols use MD5 authentication:

OSPF

RIP version 2

BGP

IP Enhanced IGRP

Key Management (Key Chains)

You can configure key chains for these IP routing protocols:

RIP version 2

IP Enhanced IGRP

DRP Server Agent

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 risk that keys will be compromised.

Each key definition within the key chain must specify a time interval for which that key is activated (its lifetime). Then, during a 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, you should ensure that for a given key chain, key activation times overlap to avoid any period of time during 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.

You can specify multiple key chains.

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 use 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 Network Management 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 listed in Table 1.

Table 1 Location of Neighbor Authentication Information for Each Supported Protocol 

Protocol
Book
Chapter
Sections

BGP

Cisco IOS IP Routing: BGP Configuration Guide

"Configuring BGP Neighbor Session Options"

"TTL Security Check for BGP Neighbor Sessions"

"Configuring the TTL Security Check for BGP Neighbor Sessions"

"Configuring the TTL-Security Check: Example"

DRP Server Agent

Cisco IOS Network Management Configuration Guide

"Configuring a DRP Server Agent"

"Authentication Keys and Keychains"

IP Enhanced IGRP

Cisco IOS IP Routing: EIGRP Configuration Guide

"Configuring EIGRP"

"Configuring EIGRP Route Authentication: Autonomous System Configuration"

"Configuring EIGRP Route Authentication: Named Configuration"

IS-IS

Cisco IOS IP Routing: ISIS Configuration Guide

"Enhancing Security in an IS-IS Network"

"Setting an Authentication Password for each Interface"

"Setting an Area Password for each IS-IS Area"

"Configuring IS-IS Authentication"

MPLS LDP

Cisco IOS Multiprotocol Label Switching Configuration Guide

"MPLS Label Distribution Protocol (LDP)"

"Protecting Data Between LDP Peers with MD5 Authentication"

OSPF

Cisco IOS IP Routing: OSPF Configuration Guide

"Configuring OSPF"

"Configuring OSPF Interface Parameters"

"Configuring OSPF Area Parameters"

"Creating Virtual Links"

RIP version 2

Cisco IOS IP Routing: RIP Configuration Guide

"Configuring Routing Information Protocol"

"Enabling RIP Authentication"


To find complete configuration information for key chains, refer to the "Managing Authentication Keys" section in the "Configuring IP Routing Protocol-Independent Features" chapter of the Cisco IOS IP Routing: Protocol-Independent Configuration Guide.