1. Evolving Toward a Self-Managing Network Jennifer Rexford Princeton University http://www.cs.princeton.edu/~jrex

2. Why is Network Management So Darn Hard? Oodles and oodles of complex features –Many protocols –Many mechanisms –Many configurable parameters Little guidance for network administrators –How to select and compose features? –How to set the configurable parameters? Managing boxes, rather than networks –Routers, switches, firewalls, IDSes, servers, etc. –Low-level, box-specific configuration languages

3. The Enemy is Complexity Goal: raising the level of abstraction –Network-level design and configuration –Composition of protocols and mechanisms Idea #1: add abstraction on top –Compile high-level spec into box configuration –But, must grapple with inherent complexity Idea #2: design system for manageability –Identify network-level abstractions –… and change the boxes and protocols –But, must grapple with backwards compatibility

4. Example: Border Gateway Protocol ASes exchange reachability information –IP prefix: block of destination IP addresses –AS path: sequence of ASes along the path Configurable routing policies –Path selection (which route to use?) –Path export (who to tell about the route?) 7018 1 88 12.34.158.5 “12.34.158.0/24: path (7018,1,88)” “12.34.158.0/24: path (88)” data traffic

5. Some Things I Hate About BGP… Routers in an AS have different views –Effect: protocol oscillation and loops –Point fix: testing sufficient conditions Routing policy distributed across routers –Effect: routers need to share information –Point fix: complex “tagging” of BGP routes Policy has only an indirect effect on traffic –Effect: selecting the right policy is hard –Point fix: “what if” tools for traffic engineering BGP route selection depends on the IGP –Effect: disruptions from small internal changes –Point fix: “what if” tools to identify risks Too distributed Too indirect

6. Interdomain Routing: Design for Manageability Routing Control Platform –Represents the AS to others –Has complete view of candidate routes –Computes answers for the AS’s routers Communicates with other ASes –Using BGP or (ideally) a brand new protocol AS 3 AS 2 AS 1 Physical peering Inter-AS Protocol RCP

7. Advantages of RCP Approach Lower management complexity –Complete, network-wide view –Direct control over the routers –Single specification of policies and objectives Simpler routers –Much less control-plane software –Much less configuration state Enabling innovation –New algorithms for selecting paths within an AS –New approaches to inter-AS routing

8. Deployability: Backwards Compatibility using BGP Border Gateway Protocol (BGP) –Protocol: messages sent between routers –Decision logic: route-selection process –Policy: configurable rules for path selection/export The key point is that BGP has –Complex decision logic and policies –Yet a simple protocol (and message format) –Use BGP messages to “program” the routers

9. Phase 1: Flexible Path Selection in One AS iBGP eBGP Before: conventional use of BGP in backbone network iBGP eBGP After: RCP learns routes and sends answers to routers RCP

10. Phase 2: AS-Wide Path Selection and Export iBGP eBGP Before: RCP gets “best” iBGP routes (and IGP feed) After: RCP gets all eBGP routes from neighbors iBGP eBGP RCP

11. Phase 3: Direct Communication Between RCPs Before: RCP gets all eBGP routes from neighbors iBGP eBGP After: ASes exchange routes via RCP RCP AS 3 AS 2 AS 1 iBGP Physical peering Inter-AS Protocol RCP

12. Systems Considerations (NSDI’05) Reliability –Problem: single point of failure –Solution: replication of RCP components Consistency –Problem: inconsistent decisions by replicas –Solution: consistency without inter-replica protocol Scalability –Problem: storing and computing for all routers –Solution: store each route once and amortize work

13. Example Network Management Applications Customer-driven route selection –Customized load-balancing policies –Geographic rules for route selection Blocking denial-of-service attacks –“Blackhole” routes that drop traffic –Only for routers carrying attack traffic Hitless maintenance –Move traffic away from certain routers –Before the operators bring down the routers

14. Conclusion Network management is too hard –IP was not designed for management –Complex, distributed operation of routers Must reduce complexity –Network-wide views and objectives –Direct control over the data plane RCP approach is feasible –Deployable, scalable, and reliable –Solves important management problems Many interesting open problems

15. Backup Slides

16. Routing Control Platform (RCP) Route Control Server (RCS) BGP Engine OSPF Viewer Routing Control Platform (RCP) Answers BGP updates … Options Topology BGP updates … OSPF link-state advertisements … Network

17. Scalability: Standard Computing Platform Prototype on a high-end PC –3.2 GHz Pentium-4 with 8 GB of RAM –Running the Linux 2.6.5 kernel Workload from the AT&T backbone –Replay the BGP and OSPF messages Good RCP performance –Memory usage: less than 2GB –Speed, BGP changes: less than 40 msec –Speed, topology changes: 0.1-0.8 seconds Short answer: the system can keep up

18. Reliability: Replication and Consistency Replication: avoid single point of failure –Multiple RCPs in a network –Connected at different places Consistency: no explicit coordination –Replica has full view of each partition –Replicas perform the same algorithm on the same data, and get the same answer RCP ARCP B A A, B B