1. Dual Homing Experiment Christian Huitema Architect Windows Networking & Communications Microsoft Corporation

2. 7/20/2002Dual homing experiment2 Simple dual homing problem statement Simple bridged network 2 routers, 2 ISP ingress filtering No ISP coordination Example 2 DSL modems DSL + cable Cable + WiFi mesh Several host Simple = IPv6 basic Advanced = multi- homing aware It must work! Single link (bridge) H H H R1 R2 ISP1 ISP2 Internet (IPv6)

3. 7/20/2002Dual homing experiment3 Define “it must work” For the simple host Can receive and send connection through either ISP If an ISP is down, continue with other For the advanced host May choose the best connection based on some heuristic May use MIPv6 to redirect connections With MIPv6, connection survives loss of one ISP.

4. 7/20/2002Dual homing experiment4 First order issue: ingress filtering Avoid the following failure scenario Host choose source address A Default route leads to router B Router B forwards the packet to ISP B Packet is dropped by ingress filtering. Possible solutions Exit router check source address, redirect packet to “right” router in case of problem Host knows which router advertises what prefix, select default router that matches source address

5. 7/20/2002Dual homing experiment5 Second issue: avoid using dead router Failure scenario Router A is dead, or link to ISP A is dead Host continue sending using source address A Router B cannot forward the packets Possible solutions Dead router stops advertising, or advertise prefix as “deprecated” Smart host detects that the router is dead, switches to other address

6. 7/20/2002Dual homing experiment6 Third issue: maintain connection Failure scenario Host has connection with peer P using address A Router A or ISP A fails Existing connections break Solution No solution for dumb host Variation of MIPV6 for smart host

7. 7/20/2002Dual homing experiment7 Fourth issue: use the right exit/entrance Failure mode Peer picks address A rather than address B Resulting traffic routed slow path Performance looks terrible Solution Need information about which address will get best performance Need MIPV6 to move connection to “better address”

8. 7/20/2002Dual homing experiment8 Further study Large networks Case 1: multilink subnet, all exit routers on same link. Case 2: routed network, all exit routers on same link. Case 3: routed network, exit routers at different location PI addressing Use a “virtual IP” solution, implemented with tunnels, as “a third connection”