1. Tokyo Institute of Technology
Multihomed ISPs and Policy Control <draft-ohta-multihomed-isps-00>
Masataka Ohta
Tokyo Institute of Technology

2. All the Hosts Should have Full (Default Free) Routing Table
Best locator of a peer from multiple ones
absence of a TLA in the table means
routing system has detected the TLA is unreachable
metric entry of the table gives preference
Metric can be set according to the policy of a site
Source address selection for ingress filtering
no forwarding or source address based routing!
use source address entry (new!) of the table
selection is hard, unless routing system is involved

3. IP Version 6 Addressing Architecture (RFC237[34])
IPv6 addresses has STRONG hierarchy
13 bits of TLA (Top Level Aggregator)
24 bits of NLA (Next Level Aggregator)
Hierarchy of ISPs is assumed
TLIs (Top Level ISPs) get globally unique TLAs
NLIs (Next Level ISPs) get NLAs unique within TLA

4. IP Version 6 Addressing Architecture
| 3| 13 | 8 | | | bits |
|FP| TLA |RES| NLA | SLA | Interface ID |
| | ID | | ID | ID | |
<--Public Topology---> Site
< >
Topology
<------Interface Identifier----->
IP Version 6 Addressing Architecture

5. Multihomed ISPs Why multihoming is necessary?
Robustness!
May NLIs be not so robust?
No!
NLIs MUST be multihomed to TLIs

6. TLI
NLI
Subscribers
Typical Scenario of IPv6 ISPs with Multihoming

7. The Question Can the number of TLAs limited? How much is the limit?
Can NLIs be happy enough that not all ISPs require TLAs
Can NLIs control policy?
How much is the limit?
No question: how the limit is imposed
to be determined by global/regional/country NICs

8. Can NLIs Control Policy?
ISPs are identified by AS#s
An NLI must peer with its TLI
the NLI may peer with any other ISP
Full egress control by NLIs possible
Ingress control?
Already limited today
locally possible if compatible with egress control

9. determined as egress ones (local arrangement negotiable)
ISP B
ISP C
ISP D
ISP E
ISP A
ISP F
ISP G
ISP H
ISP I
policy essentially
determined as egress ones
(local arrangement negotiable)
Propagation of Prefix of ISP A

10. Ingress Control Possible as long as NLA is propagated
An NLI can ask neighbor ISPs for the propagation
The NLA will be filtered by other ISPs
the NLI can still receive packets to NLA from corresponding TLA
not really a limitation

11. arrangements with D, H, E and I necessary for ingress control
ISP B
(TLI of A)
ISP C
ISP D
ISP E
ISP A
(NLI)
ISP F
ISP G
ISP H
ISP I
arrangements with D, H, E and
I necessary for ingress control
Propagation of Prefix of ISP A

12. arrangement with H fail
ISP B
(TLI of A)
ISP C
ISP D
ISP E
ISP A
(NLI)
ISP F
ISP G
ISP H
(filter NLA)
ISP I
arrangement with H fail
Propagation of Prefix of ISP A

13. Propagation of Prefix of ISP A
ISP B
(TLI of A)
ISP C
ISP D
ISP E
ISP A
(NLI)
ISP F
ISP G
ISP H
(pass NLA)
ISP I
Propagation of Prefix of ISP A

14. Propagation of Prefix of ISP A
ISP B
(TLI of A)
ISP C
ISP D
ISP E
ISP A
(NLI)
ISP F
ISP G
ISP H
(filter NLA)
ISP I
Propagation of Prefix of ISP A

15. How Much is the Limit?
A lot larger than the number of those ISPs which claims to be global (tier1)
Much larger than the number of NICs
Better to be compatible with RFC237[34]
1024~8192?

16. Conclusion NLIs must be multihomed to TLIs
NLIs policy can still be controlled
The number of TLAs should be limited below 1024~8192