IPv6 First-Hop Security Configuration Guide, Cisco IOS Release 15S
IPv6 Source Guard and Prefix Guard
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IPv6 Source Guard

IPv6 Source Guard and Prefix Guard

Last Updated: November 29, 2012

IPv6 Source Guard and IPv6 Prefix Guard are Layer 2 snooping features that validate the source of IPv6 traffic. IPv6 Source Guard blocks any data traffic from an unknown source; for example, one that is not already populated in the binding table or previously learned through Neighbor Discovery (ND) or Dynamic Host Configuration Protocol (DHCP) gleaning. IPv6 Prefix Guard prevents home-node sourcing traffic outside of the authorized and delegated traffic.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Information about IPv6 Source Guard and Prefix Guard

IPv6 Source Guard Overview

IPv6 source guard is an interface feature between the populated binding table and data traffic filtering. This feature enables the device to deny traffic when it is originated from an address that is not stored in the binding table. IPv6 source guard does not inspect ND or DHCP packets; rather, it works in conjunction with IPv6 neighbor discovery (ND) inspection or IPv6 address glean, both of which detect existing addresses on the link and store them into the binding table. IPv6 source guard is an interface between the populated binding table and data traffic filtering, and the binding table must be populated with IPv6 prefixes for IPv6 source guard to work.

IPv6 source guard can deny traffic from unknown sources or unallocated addresses, such as traffic from sources not assigned by a DHCP server. When traffic is denied, the IPv6 address glean feature is notified so that it can try to recover the traffic by querying the DHCP server or by using IPv6 ND. The data-glean function prevents the device and end user from getting deadlocked, whereupon a valid address fails to be stored into the binding table, there is no recovery path, and the end user is unable to connect.

The following illustration provides an overview of how IPv6 source guard works with IPv6 address glean:

IPv6 Prefix Guard Overview

The IPv6 Prefix Guard feature works within the IPv6 source guard feature, enabling the device to deny traffic originated from nontopologically correct addresses. IPv6 prefix guard is often used when IPv6 prefixes are delegated to devices (e.g., home gateways) using DHCP prefix delegation. The feature discovers ranges of addresses assigned to the link and blocks any traffic sourced with an address outside this range.

To determine which prefixes should be allowed and which prefixes should be blocked, IPv6 prefix guard uses the following:

  • Prefix glean in Router Advertisements (RAs)
  • Prefix glean in DHCP prefix delegation
  • Static configuration

Whenever a prefix is to be allowed, IPv6 prefix guard downloads it to the hardware table. Whenever a packet is switched, the hardware matches the source of the packet against this table and drops the packet if no match is found.

The following figure shows a service provider (SP) scenario in which prefixes are gleaned in DHCP-PD messages.

How to Configure IPv6 Source Guard and Prefix Guard

Configuring IPv6 Source Guard

SUMMARY STEPS

1.    enable

2.    configure terminal

3.   ipv6 source-guard policy snooping-policy

4.   permit link-local

5.   deny global-autoconfig

6.   trusted

7.   exit

8.   show ipv6 source-guard policy [snooping-policy]


DETAILED STEPS
Step 1   enable


Example:
Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.
Step 2   configure terminal


Example:
Device# configure terminal

Enters global configuration mode.

Step 3   ipv6 source-guard policy snooping-policy


Example:
Device(config)# ipv6 source-guard policy
Defines an IPv6 source-guard policy name and enters source-guard policy configuration mode.
Step 4   permit link-local


Example:
Device(config-source-guard)# permit link-local
Allows hardware bridging for all data traffic sourced by a link-local address.
Step 5   deny global-autoconfig


Example:
Device(config-source-guard)# deny global-autoconfig
Denies data traffic from auto-configured global addresses.
Step 6   trusted

Example:
trusted
Step 7   exit


Example:
Device(config-if)# exit
Exits source-guard policy configuration mode and places the device in privileged EXEC mode.
Step 8   show ipv6 source-guard policy [snooping-policy]
Displays the IPv6 source-guard policy configuration.

Configuring IPv6 Source Guard on an Interface

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.   ipv6 source-guard attach-policy [snooping-policy]

5.   exit

6.   show ipv6 source-guard policy [snooping-policy]


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
interface type number


Example:

Device(config)# interface fastethernet 3/13

 

Specifies an interface type and number, and places the device in interface configuration mode.

 
Step 4
ipv6 source-guard attach-policy [snooping-policy]


Example:

Device(config-if)# ipv6 source-guard attach-policy

 
Applies IPv6 source guard on an interface.  
Step 5
exit


Example:

Device(config-if)# exit

 
Exits interface configuration mode and places the device in privileged EXEC mode.  
Step 6
show ipv6 source-guard policy [snooping-policy]
 
Displays all the interfaces on which IPv6 source guard is applied.  

Configuring IPv6 Prefix Guard

SUMMARY STEPS

1.    enable

2.    configure terminal

3.   ipv6 source-guard policy snooping-policy

4.   validate address

5.   validate prefix

6.   exit

7.   show ipv6 source-guard policy [snooping-policy]


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
ipv6 source-guard policy snooping-policy


Example:

Device(config)# ipv6 source-guard policy

 
Defines an IPv6 source-guard policy name and enters source-guard policy configuration mode.  
Step 4
validate address


Example:

Device(config-source-guard)# no validate address

 
Disables the validate address feature and enables the IPv6 prefix guard feature to be configured.  
Step 5
validate prefix


Example:

Device(config-source-guard)# validate prefix

 
Enables IPv6 source guard to perform the IPv6 prefix-guard operation.  
Step 6
exit


Example:

Device(config-if)# exit

 
Exits source-guard policy configuration mode and places the device in privileged EXEC mode.  
Step 7
show ipv6 source-guard policy [snooping-policy]
 
Displays the IPv6 source-guard policy configuration.  

Configuration Examples for IPv6 Source Guard and Prefix Guard

Example: IPv6 Source Guard and Prefix Guard Configuration

Device# show ipv6 source-guard policy policy1

Policy guard configuration:
  validate prefix
  validate address

Additional References

Related Documents

Related Topic Document Title

IPv6 addressing and connectivity

IPv6 Configuration Guide

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

IPv6 commands

Cisco IOS IPv6 Command Reference

Cisco IOS IPv6 features

Cisco IOS IPv6 Feature Mapping

Standards and RFCs

Standard/RFC Title

RFCs for IPv6

IPv6 RFCs

MIBs

MIB

MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

Technical Assistance

Description Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for IPv6 Source Guard and Prefix Guard

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1 Feature Information for IPv6 Source Guard and Prefix Guard
Feature Name Releases Feature Information

IPv6 Prefix Guard

15.3(1)S

Cisco IOS XE Release 3.8S

The IPv6 Prefix Guard feature enables a device to deny traffic originated from nontopologically correct addresses.

The following commands were introduced or modified: ipv6 source-guard policy, permit link-local, show ipv6 source-guard policy, validate address, validate prefix.

IPv6 Source Guard

15.0(2)SE

15.3(1)S

Cisco IOS XE Release 3.8S

The IPv6 source guard feature blocks any data traffic sourced from an unknown source; for example, one that is not already populated in the binding table or previously learned through ND or DHCP gleaning.

The following commands were introduced or modified: deny global-autoconfig, ipv6 source-guard attach-policy, ipv6 source-guard policy, permit link-local, show ipv6 source-guard policy, trusted.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2012 Cisco Systems, Inc. All rights reserved.