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

7/11/2003Simple Multi-Homing Experiment2 Simple dual homing problem statement 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! Single link (bridge) H H H R1 R2 ISP1 ISP2 Internet (IPv6)

7/11/2003Simple Multi-Homing Experiment3 IPv4 equivalent: back-up 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 Single link (bridge) H H H R1 R2 ISP1 ISP2 Internet (IPv4)

7/11/2003Simple Multi-Homing Experiment4 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

7/11/2003Simple Multi-Homing Experiment5 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

7/11/2003Simple Multi-Homing Experiment6 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.

7/11/2003Simple Multi-Homing Experiment7 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

7/11/2003Simple Multi-Homing Experiment8 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?

7/11/2003Simple Multi-Homing Experiment9 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

7/11/2003Simple Multi-Homing Experiment10 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

7/11/2003Simple Multi-Homing Experiment11 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!

7/11/2003Simple Multi-Homing Experiment12 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#