administrivia - computer sciencesn624/552-f18/lectures/09-sdn-cp.pdf · rcp rcp rcp rcp tells...
TRANSCRIPT
![Page 1: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/1.jpg)
Administrivia• Paper assignments for reviews 2 and 3 are out
• MUD: send me your top 1—3 questions on this lecture
• Gear up for course project: Sample ideas are out• Do make friends with & team up with the others in this room• Do brainstorm your own ideas with your friends and with me• Do check with me about the “significant programming” requirement• Do make the best use of office hours starting today
![Page 2: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/2.jpg)
Lecture 9, Computer Networks (198:552)
Software-Defined Networking:Principles
![Page 3: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/3.jpg)
Traditional IP routers
Switchingfabric
Processor
Net interface
Net interface
Net interface
Net interface
Data plane
Control plane
BGPOSPF
Management plane
• Management plane• Network-wide views• Configure routers
• Control plane• Track topology• Compute routes• Install forwarding rules
• Data plane• Forward, filter, buffer,
drop, mark, rate-limit• Traffic statistics
![Page 4: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/4.jpg)
Problems with traditional routers• Management decisions tied to distributed protocols• Ex: Set OSPF link weights to force traffic through desired path• Ex: Non-deterministic network state after a link failure
• Data and control plane controlled by vendors: proprietary interfaces
?X
![Page 5: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/5.jpg)
Traditional IP network
Data plane
Data plane
Data plane
Management plane
Data plane
Control plane
Control plane
Control plane
Control plane
![Page 6: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/6.jpg)
SDN (1/2): Centralized control plane
Data plane
Data plane
Data plane
SDN controller
Data plane
Control planes lifted from switches… into a logically centralized controller… running in a compute cluster
![Page 7: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/7.jpg)
SDN (2/2): Open interface to data plane
Data plane
Data plane
Data plane
SDN controller
Data plane
![Page 8: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/8.jpg)
Some immediate consequences…
![Page 9: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/9.jpg)
(1) Simpler switches
Data plane
Data plane
Data plane
Small set of hardware instructions.
SDN controller
Data plane
![Page 10: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/10.jpg)
Data plane primitive: Match-action rules• Match arbitrary bits in the packet header
• Match on any header, or new header• Allows any flow granularity
• Actions• Forward to port(s), drop, send to controller, count,• Overwrite header with mask, push or pop, …• Forward at specific bit-rate
• Prioritized list of rules
HeaderData Match: 1000x01xx01001x
Action: fwd(port 2)
Priority: 65500
![Page 11: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/11.jpg)
(2) Network programming abstractions
Data plane
Data plane
Data plane
Application
SDN controller
Application ApplicationWrite modular apps and compose them
Data plane
![Page 12: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/12.jpg)
(3) Unified network operating system
Data plane
Data plane
Data plane
ApplicationNetwork Operating System
Application Application
Separate distributed system concerns from management policy
Data planePersist app stateGraceful failoverReplication for perf
![Page 13: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/13.jpg)
Composition of Policies
![Page 14: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/14.jpg)
Combining many networking tasks
SDN controller
Route + Monitor + FW + LB
Monolithic application
Hard to program, test, debug, reuse, port, …
![Page 15: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/15.jpg)
Modular controller applications
SDN controller
Each module partiallyspecifies the handling of the traffic
LBRouteMonitor FW
![Page 16: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/16.jpg)
Network policy as a function• Located packet: headers + switch + port
• Policy: function of a located packet• To a set of located packets: multicast, drop, forward
• Function can modify packets• Headers and location
dstip == 1.2.3.4 & srcport == 80 à port = 3, dstip = 10.0.0.1
13
2
Match Action
![Page 17: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/17.jpg)
Parallel composition (+)
SDN controller
Route on dst prefix
Monitor on source IP +
dstip == 1.2/16 à fwd(1)dstip == 3.4.5/24 à fwd(2)
srcip == 5.6.7.8 à countsrcip == 5.6.7.9 à count
srcip == 5.6.7.8, dstip == 1.2/16 à fwd(1), countsrcip == 5.6.7.8, dstip == 3.4.5/24 à fwd(2), countsrcip == 5.6.7.9, dstip == 1.2/16 à fwd(1), countsrcip == 5.6.7.9, dstip == 3.4.5/24 à fwd(2), count
![Page 18: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/18.jpg)
Example: Server load balancer• Spread client traffic over server replicas• Public IP address for the service• Split traffic based on client IP• Rewrite the server IP address
• Then, route to the replica
clients
1.2.3.4
load balancer
server replicas
10.0.0.1
10.0.0.2
10.0.0.3
![Page 19: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/19.jpg)
Sequential composition (>>)
SDN controller
RoutingLoad Balancer >>
dstip==10.0.0.1 à fwd(1)dstip==10.0.0.2 à fwd(2)
srcip==0*, dstip==1.2.3.4 à dstip=10.0.0.1srcip==1*, dstip==1.2.3.4 à dstip=10.0.0.2
srcip==0*, dstip==1.2.3.4 à dstip = 10.0.0.1, fwd(1)srcip==1*, dstip==1.2.3.4 à dstip = 10.0.0.2, fwd(2)
![Page 20: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/20.jpg)
Implications & Challenges
![Page 21: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/21.jpg)
What does SDN make possible/easy?• Expressing forwarding intent directly• Example path: sw==S1àfwd(4) + sw==S2àfwd(1) + sw==S3àfwd(7)
• Reading state: Measurement through counters• Measure exactly the traffic you care about• Can modify forwarding to make measurements more accurate!
• Deterministically and swiftly handle data plane failures• Google’s B4: Failover to pre-computed outcomes
S1 S2 S34 3 1 2 7
![Page 22: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/22.jpg)
What does SDN make possible/easy?• Network policy verification• Correctness: Reachability, loop-freedom, SLO violations, etc.• Performance
• Better router data plane design• Decouple evolution of router instruction sets and network policy
• Apply the SDN philosophy to system design as a whole• Stateful “network functions” that reside in the core of the network• Operating systems• End host NICs• <insert your idea here!>
![Page 23: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/23.jpg)
Technical challenges of SDN• Scalability: controller responsible for many routers• Response time: Delays between controller and routers• Reliability: surviving failures of the controller & data plane• Consistency: • Ensuring multiple controllers behave consistently• Ensuring controller policy is faithfully implemented
• Security: • Entire network may be owned if the controller is vulnerable
• Interoperability: legacy routers and neighboring domains
![Page 24: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/24.jpg)
Routing Control Platform (RCP)Usenix NSDI ’05
Caesar et al.
![Page 25: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/25.jpg)
Separating interdomain routing from routers• Compute interdomain routes for the routers• Input: BGP-learned routes from neighboring ASes• Output: forwarding-table entries for each router
• Backwards compatibility with legacy routers• RCP speaks to routers using iBGP protocol• Installing <destination prefix, next-hop address>
• Routers still run intradomain routing protocol• So the routers can reach the RCP • To reduce overhead on the RCP
RCP
Autonomous System
![Page 26: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/26.jpg)
Example: DoS blackholing
• Filtering attack traffic• Measurement system detects an attack• Identify entry point and victim of attack• Drop offending traffic at the entry pointRCPnull
route
DoS attack
![Page 27: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/27.jpg)
Example: Maintenance dry-out
• Planned maintenance on an edge router• Drain traffic off of an edge router• Before bringing it down for maintenance
d
egress 1
egress 2
RCPuse egress 2
![Page 28: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/28.jpg)
Example: Egress selection
•Customer-controlled egress selection• Multiple ways to reach the same destination• Giving customers control over the decision
egress 1
egress 2
data center 1
data center 2
hot-potato routing
RCPuse egress 1
customersites
![Page 29: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/29.jpg)
Example: Better BGP security
• Enhanced interdomain routing security• Anomaly detection to detect bogus routes• Prefer “familiar” routes over unfamiliar
d????egress 1
egress 2
RCPuse egress 2
d
![Page 30: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/30.jpg)
Example: Saving router memory• Reduce memory requirements on routers• Strip BGP route attributes (except prefix and next-hop)• Combine related prefixes into a single route
RCPBGP with other ASes
12.0.0.0/16 à nh 112.1.0.0/16 à nh 1
12.0.0.0/15 à nh 1
![Page 31: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/31.jpg)
Discussion of RCP• Centralizing control logic allows formalizing correctness properties• … even if the existing solutions don’t actually uphold them!• e.g., loop freedom, same egress router throughout path within AS
• Reliability, consistency, and performance from the start• Network partitions & RCP—network partitions• RCP replica failures• Processing high rates of route computations (e.g., IGP changes)
• Performance metrics & testing methodology• Message processing: delay, throughput, memory• Real-time convergence delays: may be less than iBGP-mesh• Other metrics?
![Page 32: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/32.jpg)
OpenFlow: Enabling Innovation in Campus Networks
ACM CCR ‘08McKeown et al.
![Page 33: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/33.jpg)
Program networks using simple rules• Goals: high-performance low-cost programmable switch• Be able to isolate experimental traffic on campus networks• Be consistent with vendors need for closed platforms• Restricted flexibility to keep the cost low
• Controller programs switch “flow tables” built with TCAMs• First packet of a flow allows controller to determine fwding rules• Rules can match packets against flexible field boundaries• Standardized set of actions: forward, drop, de/encapsulate• Also be able to send packet through “normal” switch processing
![Page 34: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/34.jpg)
Discussion of OpenFlow/SDN• Is match-action sufficiently expressive?
• Can switches sustain many flow processing rules and setups?• TCAM space for matches• Control overheads to install or remove flows• Memory to install packet counters for each flow
• Why fix the set of wire protocols allowed in matches?
![Page 35: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/35.jpg)
![Page 36: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/36.jpg)
Backup Slides
![Page 37: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/37.jpg)
RCP incremental deployability• Backwards compatibility• Work with existing routers and protocols
• Incentive compatibility• Offer significant benefits, even to the first adopters
AS 3AS 2AS 1
BGP
Inter-AS ProtocolRCP RCP RCP
RCP tells routers how to forward trafficUse BGP to communicate with the legacy routers
Simplify management and enable new services
Other ASes can deploy an RCP independently
ASes with RCPs can cooperate for new features
ASes can upgrade to new routing protocol
… while using BGP to control the legacy routers
![Page 38: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/38.jpg)
RCP: Scalable implementation
• Eliminate redundancy• Store a single copy of each BGP-learned route
• Accelerate lookups• Maintain indices to identify affected routers
• Avoid recomputation• Compute routes once for group of related routers
•Handle only BGP routing• Leave intradomain routing to the routers
38 An extensible, scalable, “smart” route reflector
![Page 39: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/39.jpg)
Runs on a single high-end PC
•Home-grown implementation on top of Linux• Experiments on 3.2 Ghz P4 with 4GB memory
•Computing routes for all AT&T routers• Grouping routers in the same point-of-presence
•Replaying all routing-protocol messages• BGP and OSPF logs, for 203,000 IP prefixes
• Experimental results• Memory footprint: 2.5 GB• Processing time: 0.1-20 msec
39
![Page 40: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/40.jpg)
Reliability
• Simple replication• Single PC can serve as an RCP• So, just run multiple such PCs
•Run replicas independently• Separate BGP update
feeds and router sessions• Same inputs, and the
same algorithm• No need for replica
consistency protocol40
RCP
RCP
![Page 41: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/41.jpg)
Potential consistency problem
• Need to ensure routes are consistently assigned • Even in presence of failures/partitions
• Fortunately…• Flooding-based IGP means each RCP knows what
partition(s) it connects to41
A B
C D
“Use egress C (hence use A as your next-hop)”
“Use egress D (hence use B as your next-hop)”
RCP 1 RCP 2
![Page 42: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/42.jpg)
Single RCP under partition
• Solution: Only use state from router’s partition in assigning its routes • Ensures next hop is reachable
42
Partition 1 Partition 2
RCP 1
![Page 43: Administrivia - Computer Sciencesn624/552-F18/lectures/09-sdn-cp.pdf · RCP RCP RCP RCP tells routers how to forward traffic Use BGP to communicate with the legacy routers Simplify](https://reader030.vdocuments.site/reader030/viewer/2022040115/5e77b5ad8e78c91b7a346d32/html5/thumbnails/43.jpg)
Multiple RCPs under partition
• Solution: RCPs receive same IGP/BGP state from each partition they can reach• IGP provides complete visibility and connectivity• RCS only acts on partition if it has complete state for it
43
àNo consistency protocol needed to guarantee consistency in steady state
Partition 1 Partition 2 Partition 3
RCP 2RCP 1