Simple Multihoming Experiment draft-huitema-multi6-experiment-00.txt Christian Huitema, Microsoft...
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Transcript of Simple Multihoming Experiment draft-huitema-multi6-experiment-00.txt Christian Huitema, Microsoft...
Simple Multihoming Experiment
draft-huitema-multi6-experiment-00.txtChristian Huitema, MicrosoftDavid Kessens, Nokia
7/11/2003Simple Multi-Homing
Experiment 2
Simple dual homing problem statement
Simple bridged network2 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 awareIt must work!
Single link (bridge)
H HH
R1 R2
ISP1 ISP2
Internet(IPv6)
7/11/2003Simple Multi-Homing
Experiment 3
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 HH
R1 R2
ISP1 ISP2
Internet(IPv4)
7/11/2003Simple Multi-Homing
Experiment 4
Broad Lines of the Solution
No coordination between ISPUse 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
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
7/11/2003Simple 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.
7/11/2003Simple 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
7/11/2003Simple 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?
7/11/2003Simple 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
7/11/2003Simple 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
7/11/2003Simple 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!
7/11/2003Simple 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#