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Network Architecture (R02) #4 Location and Identity

Network Architecture (R02) #4 Location and Identity. Jon Crowcroft, http://www.cl.cam.ac.uk/~jac22 http://www.cl.cam.ac.uk/teaching/1011/R02. IP addr v. Id+Loc. IP Addr == Interface + Route Hints. TCP state = 5 tuple Src+Dst port Src+Dst Addr, IP Proto Can’t change during session

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Network Architecture (R02) #4 Location and Identity

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  1. Network Architecture (R02) #4Location and Identity Jon Crowcroft, http://www.cl.cam.ac.uk/~jac22 http://www.cl.cam.ac.uk/teaching/1011/R02

  2. IP addr v. Id+Loc • IP Addr == Interface + Route Hints. • TCP state = 5 tuple • Src+Dst port Src+Dst Addr, IP Proto • Can’t change during session • If we move, have to get new addr to be reachable • Need to advertise (DNS) for new people • Need to tell old people to reconnect • Or tunnel, or rewrite to maintain TCP • Mobile IP has agents to do tunnels • Mobile IPv6 can cut the triangle case out

  3. Why not just leave as mobile ip • Don’t like triangles for ipv4 • Don’t like tunnel overhead • So what about new addr trick • Map/encap service or • IPv6 trick (8+8, for example)

  4. Re-write v. map/encap • As all said, re-write has potential security problems, but low overhead/scales in router terms • But map/encap has deployment simplicity, but o/h problems - both for encap and for binding service

  5. -ve security for re-write? • Not clear there really is a security problem • Re-writer == NAT, we trust NATs now! • E2D TCP/IP 5 tuple assumes • IPv4 I/f+route is some sort of secure thing • Never true! • Correct model is TCP state should be bound to EID, and not care about last hop of path/route at all! • Syn-cookie/nonce to secure state • Or TSL/SSL or other

  6. -ve overheads for map/encap • As currently formulated… • Fast moving device would cause a lot of re-binding • But why not try to localize this? • Movement geographically often doesn’t change provider or even topology much • Separate geo/topo/provider cases and deal with seperately?

  7. Alternative 1 - just ignore • Today, clients move; servers fixed • Move- get new IP via DHCP • Break TCP connection • HTTP recover • Cross layer optimise recovery • RTP/UDP don’t care… • Or use Multipath TCP and just add subpath transparently (make before break, though)

  8. What about both ends move? • In a way, unusual! • But if routers are also part of movement, then very “ad hoc” world - so • Make hosts routers • Believe their route updates… • Use App level recovery, or MPTCP make before break • What about new clients of re-moved servers?

  9. Alt 2 - change TCP • TCP shares state with routers today in Compressed header case • So why not cache this info • When you move, send a “SYN” packet from new addr with compressed state reset to other end (if it hasn’t moved) • And copy to router where we _were_(*) • If it has moved, then the router there • Which should have state(*) to forward it • Could generalise for all bi-dir protocols (most transport protocols have roughly symmetric packet counts)

  10. DNS • DNS update with TTL 0 is • not that big a deal! • Even the whole DNS Update rate on one large site isn’t that big a deal • www.tjd.phlegethon.org/words/thesis.pdf • Experimental results (see • Naming for Networking byAtkinson&Bhatti • http://www.cs.st-andrews.ac.uk/~saleem/publications.html • http://portal.acm.org/citation.cfm?id=1298105

  11. DNS Update rate • Locality? • In london, 10M people move over 1 hour in commute • 10^7/60*60 <10000 updates per second • This is trivial to run a transaction (secure DynDNS) for on a single machine…

  12. New topic: Scaling == Complexity? • When we ask if an architecture, system or protocol scales, what do we mean? • Computer Science defines complexity • In terms of incremental cost of algorithm in terms of input scale - e.g. • Dijkstra is O(n^2) cpu in number of routers • Link state is O(E) msgs in number of edges • A FIB might be O(ln(n)) memory re: routers

  13. Other types of complexity? • Yes - emergent properties • Synchronisation effects • Routng update-resonance • Phase shifts • Most long flow or most short (tcp congestion control regimes) • Different operating regimes • Most web data cacheable, verus most dynamic • Interactions - • Scanning worm versus routing updates • Epidemic, Pandemic, no spread • Susceptibility, Infectious, Recover, Mortality? • Other?

  14. Complex versus Complicated? • Some stuff is complicated • E.g. network configuration (CLI/IOS) • Important, but not really amenable to much CS • But could undermine safety • C.f. BGP misconfigs locally disrupt global system. • Other eg.??

  15. Next talk for 2/11/10 Naming in the Internet has been unchanged since Original DNS design, largely Look at Intential Names and Content Centric Names And discuss what new benefits they bring beyond The DNS!

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