- IPv6 Addressing and Basic Connectivity
- IPv6 Anycast Address
- IPv6 Switching: Cisco Express Forwarding and Distributed Cisco Express Forwarding Support
- Unicast Reverse Path Forwarding for IPv6
- IPv6 Services: AAAA DNS Lookups over an IPv4 Transport
- IPv6 MTU Path Discovery
- ICMP for IPv6
- ICMP for IPv6 Redirect
- IPv6 Neighbor Discovery
- IPv6 Neighbor Discovery Cache
- Enhanced IPv6 Neighbor Discovery Cache Management
- IPv6 Default Router Preference
- IPv6 Stateless Autoconfiguration
- IPv6 RFCs
IPv6 Default Router Preference
The IPv6 default router preference feature provides a coarse preference metric (low, medium, or high) for default devices.
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 Default Router Preference
Default Router Preferences for Traffic Engineering
Hosts discover and select default devices by listening to Router Advertisements (RAs). Typical default device selection mechanisms are suboptimal in certain cases, such as when traffic engineering is needed. For example, two devices on a link may provide equivalent but not equal-cost routing, and policy may dictate that one of the devices is preferred. Some examples are as follows:
- Multiple devices that route to distinct sets of prefixes--Redirects (sent by nonoptimal devices for a destination) mean that hosts can choose any device and the system will work. However, traffic patterns may mean that choosing one of the devices would lead to considerably fewer redirects.
- Accidentally deploying a new device--Deploying a new device before it has been fully configured could lead to hosts adopting the new device as a default device and traffic disappearing. Network managers may want to indicate that some devices are more preferred than others.
- Multihomed situations--Multihomed situations may become more common, because of multiple physical links and because of the use of tunneling for IPv6 transport. Some of the devices may not provide full default routing because they route only to the 6-to-4 prefix or they route only to a corporate intranet. These situations cannot be resolved with redirects, which operate only over a single link.
The default router preference (DRP) feature provides a basic preference metric (low, medium, or high) for default devices. The DRP of a default device is signaled in unused bits in RA messages. This extension is backward compatible, both for devices (setting the DRP bits) and hosts (interpreting the DRP bits). These bits are ignored by hosts that do not implement the DRP extension. Similarly, the values sent by devices that do not implement the DRP extension will be interpreted by hosts that do implement it as indicating a "medium" preference. DRPs need to be configured manually.
How to Configure IPv6 Default Router Preference
Configuring the DRP Extension for Traffic Engineering
DETAILED STEPS
Configuration Examples for IPv6 Default Router Preference
Example: IPv6 Default Router Preference
The following example displays the state of the DRP preference value as advertised by this device through an interface:
Device# show ipv6 interface gigabitethernet 0/1
GigabitEthernet0/1 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::130
Description: Management network (dual stack)
Global unicast address(es):
FEC0:240:104:1000::130, subnet is FEC0:240:104:1000::/64
Joined group address(es):
FF02::1
FF02::2
FF02::1:FF00:130
MTU is 1500 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ND DAD is enabled, number of DAD attempts: 1
ND reachable time is 30000 milliseconds
ND advertised reachable time is 0 milliseconds
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 200 seconds
ND router advertisements live for 1800 seconds
ND advertised default router preference is Low
Hosts use stateless autoconfig for addresses.
The following example displays the state of the DRP preference value as advertised by other devices:
Device# show ipv6 routers
Router FE80::169 on GigabitEthernet0/1, last update 0 min
Hops 64, Lifetime 1800 sec, AddrFlag=0, OtherFlag=0, MTU=1500
Preference=Medium
Reachable time 0 msec, Retransmit time 0 msec
Prefix FEC0:240:104:1000::/64 onlink autoconfig
Valid lifetime 2592000, preferred lifetime 604800
Additional References
Related Documents
| Related Topic | Document Title |
|---|---|
| IPv6 addressing and connectivity |
IPv6 Configuration Guide |
| Cisco IOS commands |
|
| 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: |
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. |
Feature Information for IPv6 Default Router Preference
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 Default Router Preference |
| Feature Name | Releases | Feature Information |
|---|---|---|
| IPv6 Default Router Preference |
12.2(33)SRA 12.2(33)SXH 12.2(46)SE 12.2(46)SG 12.4(2)T 15.0M 15.0(2)SG 3.2.0SG |
This feature provides a basic preference metric (low, medium, or high) for default devices. The following commands were introduced or modified: ipv6 nd router-preference, show ipv6 interface, show ipv6 router. |
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)
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.
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