Christian's IETF 56 Dual Homing Experiment

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Dual Homing Experiment
Christian Huitema
Architect
Windows Networking & Communications
Microsoft Corporation
Simple dual homing problem statement
Simple bridged network
2 routers, 2 ISP
Internet
(IPv6)


ingress filtering
No ISP coordination
Example
ISP1

ISP2


R1
Several host
R2

Single link (bridge)
H
7/20/2002
H
2 DSL modems
DSL + cable
Cable + WiFi mesh
H

Simple = IPv6 basic
Advanced = multihoming aware
It must work!
Dual homing experiment
2
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



7/20/2002
May choose the best connection based on
some heuristic
May use MIPv6 to redirect connections
With MIPv6, connection survives loss of
one ISP.
Dual homing experiment
3
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


7/20/2002
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
Dual homing experiment
4
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


7/20/2002
Dead router stops advertising, or advertise
prefix as “deprecated”
Smart host detects that the router is dead,
switches to other address
Dual homing experiment
5
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


7/20/2002
No solution for dumb host
Variation of MIPV6 for smart host
Dual homing experiment
6
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


7/20/2002
Need information about which address will
get best performance
Need MIPV6 to move connection to “better
address”
Dual homing experiment
7
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

7/20/2002
Use a “virtual IP” solution, implemented
with tunnels, as “a third connection”
Dual homing experiment
8
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