All about homing

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

2. 7/11/2003 Simple Multi-Homing Experiment 2
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)

3. 7/11/2003 Simple 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 H
H
R1 R2
ISP1 ISP2
Internet
(IPv4)

4. 7/11/2003 Simple Multi-Homing Experiment 4
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

5. 7/11/2003 Simple 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

6. 7/11/2003 Simple 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. 7/11/2003 Simple 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

8. 7/11/2003 Simple 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?

9. 7/11/2003 Simple 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

10. 7/11/2003 Simple 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

11. 7/11/2003 Simple 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!

12. 7/11/2003 Simple 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#