Dual Homing Experiment

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Dual Homing Experiment

• Christian HuitemaArchitect
• Windows Networking CommunicationsMicrosoft
  Corporation

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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!

Internet (IPv6)
ISP1
ISP2
R1
R2
Single link (bridge)
H
H
H
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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.

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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

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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

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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

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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

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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