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Default Router Preferences and More-Specific Routes in RAs

Default Router Preferences and More-Specific Routes in RAs. draft-draves-ipngwg-router-selection-01. Richard Draves March 19, 2001 Minneapolis IETF Meeting. What is this about?. An OPTIONAL extension to Neighbor Discovery. Puts extra information in RAs. Preference for the default router.

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Default Router Preferences and More-Specific Routes in RAs

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  1. Default Router Preferences andMore-Specific Routes in RAs draft-draves-ipngwg-router-selection-01 Richard DravesMarch 19, 2001 Minneapolis IETF Meeting

  2. What is this about? • An OPTIONAL extension to Neighbor Discovery. • Puts extra information in RAs. • Preference for the default router. • More-specific routes, with lifetimes and preferences. • Helps hosts pick a router for off-link destinations.

  3. What’s it good for? • Multi-homed hosts • Redirects don’t work. • ND gives no guidance • Multi-homing is increasingly frequent • Wireless interfaces • VPN tunnel interfaces • v6/v4 configured tunnel interfaces • 6over4 interfaces

  4. Why use Router Advertisements? • Existing standard, stable interface for router->host communication. • Insulates host from plethora of routing protocols and allows for independent evolution. • Similarly, IGMP/MLD insulates host from multicast routing. • No additional message traffic. • Hosts already receive & parse RAs.

  5. Configuration of Preferences and More-Specific Routes • Preferences are very simple and coarse:High, Medium, Low • Routers do NOT advertise all their routes. • Administratively configured. • No direct mapping from routing table.

  6. Changes to RA Header • 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 ...+-+-+-+-+-+-+-+-+-+-+-+-

  7. Route Information Option • 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|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Route Lifetime |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |+ Prefix...

  8. Conceptual Model • Unchanged. Ignores preferences/routes. • Uses default router preferences, ignores routes. Does not have a routing table. • Uses preferences and routes. • Has a routing table and uses routes, but ignores preferences.

  9. Conceptual Routing Table • Replaces Default Router List • May replace On-Link Prefix List • Entries have • Prefix, prefix length. • Lifetime. • Preference. • Next-hop router.

  10. Conceptual Sending Algorithm For off-link destinations, • When selecting a route in the routing table, look at matching routes: • Prefer reachable routers over unreachable. • Prefer longer matches over shorter. • Use route preference values. • If the matching routers are all unreachable, round-robin among them all regardless of prefix length or preference values.

  11. Configuration Scenarios • A router that is not connected to the Internet, or connected through a firewall, may advertise itself with Low preference. • A router may advertise specific routes for directly connected subnets and shorter prefixes (eg, site, NLA, TLA). • More advanced configurations require administrative coordination among routers

  12. Usage Scenarios • Home user creates VPN into corp network • ISP advertises Normal preference for ::/0 • VPN advertises Low preference for ::/0, plus Normal preference for the site prefix • Home user with two ISPs • Each ISP advertises its NLA/TLA prefix

  13. What next? • Progress towards proposed standard, informational, or experimental? • IANA assignment of option type?

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