End-to-end Multihoming <draft-ohta-e2e-multihoming-00.txt> Masataka Ohta mohta@necom830.hpcl.titech.ac.jp

THE PROBLEM Full Routing Table Too Large because of random IPv4 address allocation to be solved with IPv6 because of Multihoming # of TLAs should be controlled below what? below 1,000 seems to be easy below 100 is not difficult, hopefully

TLI SLI Subscribers Typical Scenario of IPv6 Multihoming

1 1 1 1 1 TLI 2 3 3 2 2 SLI 5 3 8 2 4 Subscribers Number of Prefixes with E2E Multihoming

Multihoming Typical IPv4 multihoming Advertise an address range through multiple (not necessarily 2) routes Explosion of # of routing table entries # of ASes

Rest of the Internet ISP A ISP B Multihomed Site Singly Homed Site H

Multihoming by (Intelligent) Routing Rest of the Internet １３１．１１２．０．０／１６、 １３１．１１３．０．０／１６ １３１．１１２．０．０／１６ ISP A ISP B １３１．１１３．０．０／１６ １３１．１１２．０．０／１６ １３１．１１２．０．０／１６ Multihomed Site Singly Homed Site H Multihoming by (Intelligent) Routing

Multihoming by (Intelligent) Routing Rest of the Internet １３１．１１２．０．０／１5 １３１．１１２．０．０／１６ ISP A ISP B １３１．１１３．０．０／１６ １３１．１１２．０．０／１６ １３１．１１２．０．０／１６ Multihomed Site Singly Homed Site H Multihoming by (Intelligent) Routing

End to End Multihoming (1) A host has multiple addresses Application or transport tries all the destination addresses Each address range can be aggregated No routing table entry explosion No AS number explosion

End to End Multihoming (2) When to Try Alternative Addresses? Application/Transport dependent Controlled by the intelligence of end systems TCP will have a default timeout period Which Address Should be Tried Next? Routing table can give hints Lack of a routing table entry means lack of reachability to a host Existence of an aggregated routing table entry does not mean reachability to the host Metric information in routing table can help too

Rest of the Internet ISP A ISP B Multihomed Site Singly Homed Site H １３１．０．０．０／８ １３３．０．０．０／８ ISP A ISP B １３１．１１３．０．０／１６ １３１．１１２．０．０／１６ １３３．１１２．０．０／１６ Multihomed Site Singly Homed Site H １３３．１１２．３２．１３２， １３１．１１２．３２．１３２ End to End Multihoming

Because It IS End to End No change to router functionality MUST change API on hosts Or the hosts are singly homed Wrong to assume Intelligent routers help dumb nodes A host can and is recommended to have a default free global (but now small) routing table A real dumb host is dumb and singly homed

Do Intelligent End Systems Require Standard IGP? No. Standard protocol to distribute (but not compute) routing table to hosts is required RIPv2 (with metric >15) seems to be good enough. Or RA? BGP routers generate metric from policy based preference

Source Address Selection? Wrong topic for multihoming Both sources select destination addresses At the destination, reverse & forward DNS lookup of source address gives all the address of the source The destination selects an appropriate destination address for reply No source address selection by source meaningful Or, protocols may be modified to carry them

TCP API/Protocol Changes Source have no reachability information of SYNACK reply addresses at the destination Destination should select the address Multiple PCB entries for a connection How to give the multiple addresses of the source to the destination? DNS? Let SYN carry all the addresses?

DNS Changes DNS can not give addresses for DNS reply Clients should choose source address reachable from the name server First, choose randomly Should (re)try with other source addresses A lot of delay Or, change protocol? Query carries all the addresses of the source

End to End Multihoming and DNS/SMTP DNS and SMTP servers already deploy E2E multihoming NS/MX servers may have multiple A records If a server has multiple addresses All the addresses are tried It is of course as the most important, required-to-be-rubust applications of the Internet

8+8 DNS reverse lookup by lower 8 bytes only Hosts are identified by lower 8 bytes (IID) A compact DNS name carried by all the packets of all the protocols Makes modification to application/transport protocols for E2E multihoming easier Not Mike O’dell’s GSE one (violate E2E) Teraoka san will present his version (8+5)