IPv6 Configuration Guide, Cisco IOS Release 15.2M&T
IPv6 Default Router Preference
IPv6 Default Router Preference
Last Updated: July 31, 2012
The IPv6 default router preference feature provides a coarse preference metric (low, medium, or high) for default devices.
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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:
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
Perform this task to configure the DRP extension to RAs, which signals the preference value of a default device.SUMMARY 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
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.
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