RFC 4191 Router Preferences and More-Specific Routes Speaker: Ching-Chen Chang Date: 20070612

Outline Introduction Preference Value The Format of message Conceptual Model of Host Example Reference

Introduction An optional extension to Neighbor Discovery Router Advertisement messages for communicating default router preferences and more-specific routes from routers to hosts. using Neighbor Discovery Router Advertisement are an existing standard and stable protocol. Shielding the host from having to participate in more router-to-router interactons. It carries route lifetimes.

Preference Value 01 High 00 Medium 11 Low 10 Reserved

The Format of message(1/3) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 ++++++++++++++++++++++++++++++++++++++++++++++ | Type | Code | Checksum | | Cur Hop Limit |M|O| Reserved | Router Lifetime | | Reachable Time | | Retrans Timer | | Options |

The Format of message(2/3) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 ++++++++++++++++++++++++++++++++++++++++++++++ | Type | Code | Checksum | | Cur Hop Limit |M|O|H| Prf |Resvd | Router Lifetime | | Reachable Time | | Retrans Timer | | Options | Prf => Default Router Preference

The Format of message(3/3) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 ++++++++++++++++++++++++++++++++++++++++++++++ | Type | Length | Prefix Length |Resvd|Prf|Resvd| | Router Lifetime | | Prefix (Variable Length) | . .

Conceptual Model of Host Type A: Neighbor Discovery. Type B: Hosts uses a Default Router List augmented with preference values, but ignore all Route Information Options. Type C: Hosts use a Routing Table instead of a Default Router List.

Example ::/0 -> router W with a Medium prefrence 2002::/16 -> router X with a Medium preference 2001:db8::/32 -> router Y with a High preference 2001:db8::/32 -> router Z with a Low preference

Reference RFC 4191 Default Router Preferences and More-Specific Routes http://www.faqs.org/rfcs/rfc4191.html RFC 3775 Mobility Support in IPv6 http://www.faqs.org/rfcs/rfc3775.html RFC 2461 Neighbor Discovery for IP Version 6 http://www.faqs.org/rfcs/rfc2461.html