15-744: Computer NetworkingNew Routing IdeasOutlineMulti-homingMulti-homing to Multiple ProvidersAddress Space from one ISPPitfallsAddress Space from Both ISPsAddress Space Obtained IndependentlySlide 10Origin MisconfigurationExport MisconfigurationInteresting Observations - Origin MisconfigInteresting Observations - Export MisconfigSlide 15Overlay RoutingOverlay for FeaturesExamplesOverlay for Performance [S+99]Quantifying Performance LossBandwidth EstimationPossible Sources of Alternate PathsOverlay ChallengesFuture of OverlaySlide 25Why Active Networks?Active NetworksWhy not IP?Variations on Active NetworksCase Study: MIT ANTS SystemSystem ComponentsCapsulesSlide 33Slide 34Slide 35Research QuestionsFunctions Provided to CapsuleSafety, Resource Mgt, SupportApplications/ProtocolsDiscussionNext Lecture: TCP Reliability15-744: Computer NetworkingL-6 Routing IssuesL -6; 2-26-02© Srinivasan Seshan, 2002 2New Routing Ideas•Border Gateway Protocol (BGP) cont.•Overlay networks•Active networks•Assigned reading•[S+99] The End-to-End Effects of Internet Path Selection•[W99] Active network vision and reality: lessons from a capsule-based systemL -6; 2-26-02© Srinivasan Seshan, 2002 3Outline•Multi-Homing•BGP Misconfiguration•Overlay Routing•Active NetworksL -6; 2-26-02© Srinivasan Seshan, 2002 4Multi-homing•With multi-homing, a single network has more than one connection to the Internet.•Improves reliability and performance:•Can accommodate link failure•Bandwidth is sum of links to Internet•Challenges•Getting policy right (MED, etc..)•AddressingL -6; 2-26-02© Srinivasan Seshan, 2002 5Multi-homing to Multiple Providers•Major issues:•Addressing•Aggregation•Customer address space:•Delegated by ISP1•Delegated by ISP2•Delegated by ISP1 and ISP2•Obtained independentlyISP1 ISP2ISP3CustomerL -6; 2-26-02© Srinivasan Seshan, 2002 6Address Space from one ISP•Customer uses address space from ISP1•ISP1 advertises /16 aggregate•Customer advertises /24 route to ISP2•ISP2 relays route to ISP1 and ISP3•ISP2-3 use /24 route•ISP1 routes directly•Problems with traffic load?138.39/16138.39.1/24ISP1 ISP2ISP3CustomerL -6; 2-26-02© Srinivasan Seshan, 2002 7Pitfalls•ISP1 aggregates to a /19 at border router to reduce internal tables.•ISP1 still announces /16.•ISP1 hears /24 from ISP2.•ISP1 routes packets for customer to ISP2!•Workaround: ISP1 must inject /24 into I-BGP.138.39.0/19138.39/16ISP1 ISP2ISP3Customer138.39.1/24L -6; 2-26-02© Srinivasan Seshan, 2002 8Address Space from Both ISPs•ISP1 and ISP2 continue to announce aggregates•Load sharing depends on traffic to two prefixes•Lack of reliability: if ISP1 link goes down, part of customer becomes inaccessible.•Customer may announce prefixes to both ISPs, but still problems with longest match as in case 1.138.39.1/24204.70.1/24ISP1 ISP2ISP3CustomerL -6; 2-26-02© Srinivasan Seshan, 2002 9Address Space Obtained Independently•Offers the most control, but at the cost of aggregation.•Still need to control paths•Some ISP’s ignore advertisements with long prefixesISP1 ISP2ISP3CustomerL -6; 2-26-02© Srinivasan Seshan, 2002 10Outline•Multi-Homing•BGP Misconfiguration•Overlay Routing•Active NetworksL -6; 2-26-02© Srinivasan Seshan, 2002 11Origin Misconfiguration•Can only tell additions not omissionsOld Route New RouteSelf deaggregation a.b.0.0/16 X Y Z a.b.c.0/24 X Y ZRelated origin a.b.0.0/16 X Y Z a.b.0.0/16 X Ya.b.0.0/16 X Y Z Oa.b.c.0/24 X Ya.b.c.0/24 X Y Z OForeign origin a.b.0.0/16 X Y Z a.b.0.0/16 X Y Oa.b.c.0/24 X Y Oe.f.g.h/i X Y OL -6; 2-26-02© Srinivasan Seshan, 2002 12Export Misconfiguration•Need desired policy inferred from announcementsExport Policy ViolationProvider AS ProviderRoute exported to provider was imported from a providerProvider AS PeerRoute exported to peer was imported from a providerPeer AS ProviderRoute exported to provider was imported from a peerPeer AS PeerRoute exported to peer was imported from a peerL -6; 2-26-02© Srinivasan Seshan, 2002 13Interesting Observations - Origin Misconfig•Results•72% of new routes may be misconfig•11-13% of incidents (4% of prefixes) affect connectivity•But only identify addition of origins•Should really evaluate % of connectivity problems come from misconfig•Mostly from self-deaggregation•Problems from foreign origin•Causes•Router bugs (initialization)•Reliance on upstream filtering•Old config files•Links to IGP•HijacksL -6; 2-26-02© Srinivasan Seshan, 2002 14Interesting Observations - Export Misconfig•Primarily causes extra traffic•Causes•Export policies based on prefix based configuration•Export client’s prefix from one provider to anotherP1 P2AC•Intended policy: Provide transit to C through link A-C•Configured policy: Export all routes originated by C to P1 and P2L -6; 2-26-02© Srinivasan Seshan, 2002 15Outline•Multi-Homing•BGP Misconfiguration•Overlay Routing•Active NetworksL -6; 2-26-02© Srinivasan Seshan, 2002 16Overlay Routing•Basic idea:•Treat multiple hops through IP network as one hop in “virtual” overlay network•Run routing protocol on overlay nodes•Why?•For performance – can run more clever protocol on overlay•For functionality – can provide new features such as multicast, active processing, IPv6L -6; 2-26-02© Srinivasan Seshan, 2002 17Overlay for Features•How do we add new features to the network?•Does every router need to support new feature?•Choices•Reprogram all routers active networks•Support new feature within an overlay•Basic technique: tunnel packets •Tunnels•IP-in-IP encapsulation•Poor interaction with firewalls, multi-path routers, etc.L -6; 2-26-02© Srinivasan Seshan, 2002 18Examples•IP V6 & IP Multicast•Tunnels between routers supporting feature•Mobile IP•Home agent tunnels packets to mobile host’s location•QOS•Needs some support from intermediate routers maybe not?L -6; 2-26-02© Srinivasan Seshan, 2002 19Overlay for Performance [S+99]•Why would IP routing not give good performance?•Policy routing – limits selection/advertisement of routes•Early exit/hot-potato routing – local not global incentives•Lack of performance based metrics – AS hop count is the wide area metric•How bad is it really?•Look at performance gain an overlay providesL -6; 2-26-02© Srinivasan Seshan, 2002 20Quantifying Performance
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