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Simple Multihoming Experiment

Simple Multihoming Experiment. draft-huitema-multi6-experiment-00.txt Christian Huitema, Microsoft David Kessens, Nokia. Simple bridged network 2 routers, 2 ISP ingress filtering No ISP coordination Example T1 + DSL back-up 2 DSL modems DSL + cable Cable + WiFi mesh Several hosts

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Simple Multihoming Experiment

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  1. Simple Multihoming Experiment draft-huitema-multi6-experiment-00.txt Christian Huitema, Microsoft David Kessens, Nokia

  2. Simple bridged network 2 routers, 2 ISP ingress filtering No ISP coordination Example T1 + DSL back-up 2 DSL modems DSL + cable Cable + WiFi mesh Several hosts Simple = IPv6 basic Advanced = multi-homing aware It must work! Simple dual homing problem statement Internet (IPv6) ISP1 ISP2 R1 R2 Single link (bridge) H H H Simple Multi-Homing Experiment

  3. Use for Back-Up Switch R1 on if R2 is down May incur small delay In general, loose TCP connections Typically combined with NAT & DHCP Private addresses, no renumbering IPv4 equivalent: back-up Internet (IPv4) ISP1 ISP2 R1 R2 Single link (bridge) H H H Simple Multi-Homing Experiment

  4. Broad Lines of the Solution • No coordination between ISP • Use of Provider Addresses • Each ISP allocates a prefix • or each ISP allocates an IPv4 address, and the routers use 6to4 • Multi-Addressing • Each router advertises a prefix • Hosts configure addresses with each prefix • Five issues need resolution Simple Multi-Homing Experiment

  5. Multi-addressing issues • Ingress filtering • host pick address from ISP1, send through R2? • Dead default exit router, or dead ISP • host keeps sending packets through a black hole? • Inbound connection through wrong ISP • Peers send packet to the black-holes address? • Maintaining TCP connections • Keep TCP going if the Router or the ISP fails? • Use the right exit/entrance • Maybe some amount of load balancing Simple Multi-Homing Experiment

  6. Ideas, Ingress Filtering • Choice by host • Host treats multiple “auto-config” prefixes as “sub-interfaces”, associates individual IPv6 address and default router. • Easy to implement in “new hosts”. • Redirect at routers • No need for tunnels in single link network. • Guarantees that “old hosts” keep working. • There may be other solutions • New services, ISP involvement, etc. Simple Multi-Homing Experiment

  7. Ideas, dead exit router or dead ISP • If the router notices the problem • Advertises prefix as “deprecated”, or stop advertising • Will not be used for new connections • Will work for old and new hosts. • If the problem is not really detected • New host tries multiple source addresses when establishing a new connection • Host may keep track of the quality of each router connection Simple Multi-Homing Experiment

  8. Ideas, Peer using dead address • If the problem is detected • Update the name server? • If the problem is not detected • DNS advertises multiple addresses • Peer tries several addresses • Issue: TCP timers? Simple Multi-Homing Experiment

  9. Ideas, Maintaining TCP Connections • No good solution for old hosts • But there is no solution in a similar IPv4 set-up either • Many applications will automatically reconnect • New hosts may use MIPv6 • See “Application of the MIPv6 protocol to the multi-homing problem” • draft-bagnulo-multi6-mnm-00 • SCTP may also be used • See “multi-homing issues in SCTP” • draft-coene-sctp-multihome-04.txt Simple Multi-Homing Experiment

  10. Idea, Selecting the right exit/entrance • Right entrance: DNS tricks • In asymmetric scenarios (back-up), only publish the “best address” in the DNS • In symmetric scenarios, publish both • Right exit: Routing tricks • Provide information in router announcement, as in “Default Router Preferences, More-Specific Routes, and Load Sharing “ • draft-ietf-ipv6-router-selection-02.txt Simple Multi-Homing Experiment

  11. Summary • It looks good on paper • All issues have plausible solutions • No change required to IPv6 standards • No need to rewrite the IPv6 address at site exit • We would benefit from “mobile IPv6” and “router selection” work • But we would like an actual deployment… • In theory, there is no difference between theory and practice, but in practice there is! Simple Multi-Homing Experiment

  12. Range of solutions • Small sites • Do as we just explained • Medium sites • Ask the ISP to cooperate, allow both source addresses in ingress filtering • E.g. add a local route to the other prefix • Very large sites • Treat as ISP, get their own prefix & AS# Simple Multi-Homing Experiment

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