1. 1 Route Control Platform – IEEE CCW 2004 Route Control Platform Making an AS look and act like one router Aman Shaikh AT&T Labs - Research IEEE CCW 2004 Matt Caesar (UC Berkeley) Don Caldwell (AT&T Labs – Research) Nick Feamster (MIT) Jennifer Rexford (AT&T Labs – Research) Kobus van der Merwe (AT&T Labs – Research)

2. 2 Route Control Platform – IEEE CCW 2004 BGP = “Broken” Gateway Protocol??? BGP is broken –It converges slowly –At times it does not converge at all –It causes routing loops and deflections inside an AS –It’s misconfigured frequently –Traffic engineering is hard with BGP Fixing BGP is hard –Incremental fixes Makes BGP even more complicated –New architectures and inter-domain protocols Deployment is almost impossible

3. 3 Route Control Platform – IEEE CCW 2004 What are the Fundamental Problems? AS is a logical entity for inter-domain routing (i.e. BGP) and yet BGP state and logic are decomposed across routers inside an AS –No router has complete BGP state –Each router makes routing decision based on partial and incomplete state BGP interacts in odd ways with other protocols –Most notably with the IGP (Interior Gateway Protocol) running inside an AS

4. 4 Route Control Platform – IEEE CCW 2004 Fixing the Fundamental Problems Treat the AS as a single logical entity –Compute routes using AS-wide state Control routing protocol interactions Principles for inter-domain routing!

5. 5 Route Control Platform – IEEE CCW 2004 Applying the Principles: Route Control Platform (RCP) Represents an AS as a single logical entity –Complete view of AS’s routes –Computes routes for all routers inside an AS Routers no longer have to compute routes Controls BGP-IGP interactions Exchanges routing information with RCPs in other ASes AS 3 AS 2 AS 1 iBGP Physical peering Inter-AS Protocol RCP

6. 6 Route Control Platform – IEEE CCW 2004 The rest of this Talk: The Case for RCP How current routing infrastructure violates the principles of inter-domain routing –Treat the AS as a single logical entity –Control routing protocol interactions Potential deal-breakers for RCP –Backwards compatibility and deployment incentives –Scalability and reliability Related work (or…haven’t we seen this before?) –Route reflection and route servers –Overlay networks

7. 7 Route Control Platform – IEEE CCW 2004 Routing in the Internet Internet is a collection of Autonomous Systems (ASes) –BGP : routing between ASes –IGP (Interior Gateway Protocol): routing within AS Example: OSPF, IS-IS, RIP AS1AS2 AS3AS4AS5 OSPF RIP OSPF IS-IS BGP

8. 8 Route Control Platform – IEEE CCW 2004 BGP Route Distribution inside AS Use of iBGP (internal BGP) for route distribution Routers have to form a full mesh of iBGP sessions –Full mesh does not scale beyond few tens of routers Use of “route reflectors” to solve scalability problem –Leads to information hiding –Scalability at the expense of visibility iBGP Route Reflectors

9. 9 Route Control Platform – IEEE CCW 2004 d 11 10 A B C BGP-IGP Interaction BGP route selection process uses IGP costs to tie-break between equally good egress points –If multiple egress points, choose the one with shortest IGP path (known as “hot potato” routing) Once egress-point is selected, BGP relies on IGP to reach the egress point d 9 10 AB C Path cost change due to failure, traffic engineering or maintenance

10. 10 Route Control Platform – IEEE CCW 2004 Example of a Forwarding Loop RR1RR2 C1 C2 33 1 11 d C1 learns BGP route to destination from RR1 C2 learns BGP route to destination from RR2 C1 sends packets to RR1 via its IGP shortest path which traverses C2 Persistent forwarding loop  C2 sends packets to RR2 via its IGP shortest path which traverses C1

11. 11 Route Control Platform – IEEE CCW 2004 Avoiding Forwarding Loops with RCP RCP learns all externally learned routes Computes consistent router-level paths Benefits: –Intrinsic loop freedom and faster convergence –RCP does not have to stick to BGP decision process Can “pin” paths for traffic engineering and other purposes RR1RR2 C1 C2 33 1 11 d “RR2” RCP

12. 12 Route Control Platform – IEEE CCW 2004 Deployment in Three Steps Two key issues –Backward compatibility –Deployment incentives AS 3 AS 2 AS 1 iBGP Physical peering Inter-AS Protocol RCP iBGP eBGP

13. 13 Route Control Platform – IEEE CCW 2004 Phase 1: Control over Protocol Interactions iBGP eBGP Before: conventional iBGP iBGP eBGP After: RCP gets “best” iBGP routes (and IGP topology) Only one AS has to change its architecture! RCP

14. 14 Route Control Platform – IEEE CCW 2004 Phase 1 Application: Controlling Path Changes BGP routes take “nearest exist” (shortest IGP path) Failures or maintenance can change IGP (path) weights Exit point can also change Traffic shifts, convergence delay, congestion d 9 10 11 10 A A B B C C Path cost change due to failure, traffic engineering or maintenance d

15. 15 Route Control Platform – IEEE CCW 2004 Phase 1 Application: Controlling Path Changes BGP routes take “nearest exist” (shortest IGP path) Failures or maintenance can change IGP (path) weights RCP can “pin” exit points as IGP weights change 11 10 A B C Path cost change due to failure, traffic engineering or maintenance RCP

16. 16 Route Control Platform – IEEE CCW 2004 Phase 2: AS-wide Selection and Policy iBGP eBGP Before: RCP gets “best” iBGP routes (and IGP topology) After: RCP gets all eBGP routes from neighbors iBGP eBGP RCP

17. 17 Route Control Platform – IEEE CCW 2004 Phase 2 Application: Centralize Configuration Sprint UUNet A C 10.0.0.1192.168.0.1 Simple policy: “Don’t advertise routes learned from UUNet to Sprint” Configuration is decomposed, so routes must carry state neighbor 192.168.0.1 route-map IMPORT-C in route-map IMPORT-C permit 10 set community 0:1000 Assign routes “From UUNet” tag at router C ip community-list 1 permit 0:1000 neighbor 10.0.0.1 route-map EXPORT-A out route-map EXPORT-A deny 10 match community 1 Don’t send route with “From UUNet” tag to Sprint at router A

18. 18 Route Control Platform – IEEE CCW 2004 RCP implements policies for entire AS –Knows about sessions to all other ASes –Implements policies in terms of relationship with Ases Today’s router configuration cannot capture this Benefits –Simpler configuration –Do not have to tag routes with state Sprint UUNet A C 10.0.0.1192.168.0.1 RCP Phase 2 Application: Centralize Configuration

19. 19 Route Control Platform – IEEE CCW 2004 Phase 3: All ASes have 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

20. 20 Route Control Platform – IEEE CCW 2004 Phase 3 Application: More Flexible Routing Better network management –Diagnostics and trouble-shooting –Routing co-located with other information (e.g. traffic) –Ability to reason about an AS as a single entity Protocol Improvements –Routing based on optimization of resources (or some other criteria) instead of kludgy things like “hot-potato” –Attaching prices to routes –Inter-AS negotiation of exit points –Overlay routing informed by IP-layer information Your application here…

21. 21 Route Control Platform – IEEE CCW 2004 Scalability and Robustness Can RCP scale? –We have a prototype implementation Single-box RCP can handle AS-wide BGP load OSPF changes can be troublesome! –Centralized != unable to scale Is RCP a single point of failure? –RCP can be implemented using distributed system insights –Consistency (mostly) a non-isssue Guarantee from OSPF/IS-IS operation: –“Either an RCP replica has a complete view of network (partition) or no view; but never a partial view”

22. 22 Route Control Platform – IEEE CCW 2004 Is RCP basically a Route Reflector? Yes, but it’s a better route reflector “Customized” routing decisions for clients –Route reflectors do not compute routes from client’s perspective –Route reflectors do not emulate a “full mesh” Routing decisions based on complete visibility –Guaranteed correct routes Replication is dictated by system issues

23. 23 Route Control Platform – IEEE CCW 2004 RCP also looks a lot like… A “route server” –Route arbiter: looked at applying policy at exchange points –AS agents RCP can act as an AS agent; can answer queries for the AS An overlay network –Most previous work is in data overlays –RCP is a control overlay Hierarchical routing is about control overlays –RCP could give more information and control to data overlays RCP has AS-wide information and direct control over paths taken through the AS

24. 24 Route Control Platform – IEEE CCW 2004 Conclusions RCP embodies two principles for inter-domain routing –Treat an AS as a single logical entity Compute consistent routes using complete AS-wide view –Control routing protocol interactions Benefits –Simpler, more expressive configuration –Intrinsic robustness: no loops, faster convergence –Enable new applications and innovations Opportunity for new traffic engineering applications

25. 25 Route Control Platform – IEEE CCW 2004 More information FDNA 04 paper “The Case for Separating Routing from Routers” Nick Feamster, Hari Balakrishnan, Jennifer Rexford, Aman Shaikh, Kobus van der Merwe http://www.research.att.com/~ashaikh/publications.html Questions??

26. 26 Route Control Platform – IEEE CCW 2004 Backup

27. 27 Route Control Platform – IEEE CCW 2004 Phase 2 Application: Efficient Aggregation 192.168.0.0/23 192.168.0.0/24 192.168.0.0/23 192.168.1.0/24 192.168.0.0/23 (??) iBGP eBGP Aggregation curbs routing table growth Routers can’t know which routers need more specific routes

28. 28 Route Control Platform – IEEE CCW 2004 Phase 2 Application: Efficient Aggregation 192.168.0.0/23 192.168.0.0/24 192.168.0.0/23 192.168.1.0/24 192.168.0.0/23 Aggregation curbs routing table growth 192.168.0.0/24 192.168.1.0/24 192.168.0.0/23 RCP RCP can determine which routers need more specific routes and which routers can do away with less specific routes

29. 29 Route Control Platform – IEEE CCW 2004 Phase 1 Application: Controlling Path Changes BGP routes take “nearest exist” (shortest IGP path) Failures or maintenance can change IGP (path) weights Exit point can also change Traffic shifts, convergence delay, congestion A B CD

30. 30 Route Control Platform – IEEE CCW 2004 Phase 1 Application: Controlling Path Changes BGP routes take “nearest exist” (shortest IGP path) Failures or maintenance can change IGP (path) weights RCP can “pin” exit points as IGP weights change RCP A B CD