Shadow MACs: Scalable Label-switching
 for Commodity Ethernet Kanak Agarwal, Colin Dixon*, Eric Rozner, John Carter
 IBM Research, Austin, TX * now at Brocade 1 SDN: The Future! Rose-colored glasses: 
 • Fine-grained, dynamic control of the network Supported by: • Flow mod’s based on diverse set of pkt hdr fields • Network measurements obtained in milliseconds1 • Flow mods installed hundreds of times a second2 • 1. Rasley, et al. Planck: Millisecond-scale Monitoring and Control for Commodity Networks. SIGCOMM’14. 2. Rostos et al. OFLOPS: An Open Framework for OpenFlow Switch Evaluation. PAM’12. 2 SDN: The Future! Rose-colored glasses: 
 • Fine-grained, dynamic control of the network Supported by: • o d t e m i t • Flow mod’s based on divemresen t ss e l ti of pkt hdr fields o y p l M o s t S D N d e a l l p r o d u c t i o n m o r s a y s Network moevaesrul rements obtanint es d in milliseconds1 • m e n n v i r o e Flow mods installed hundreds of times a second2 • 1. Rasley, et al. Planck: Millisecond-scale Monitoring and Control for Commodity Networks. SIGCOMM’14. 2. Rostos et al. OFLOPS: An Open Framework for OpenFlow Switch Evaluation. PAM’12. 3 SDN: The Future? Significant issues can arise at scale! • Flow mod’s based on diverse set of pkt hdr fields • TCAMs expensive, only few 1,000 rules supported ! Network measurements obtained in milliseconds • Flow mods installed hundreds of times a second • Consistent network updates are hard! 4 Label Switching to the Rescue! Label switching common forwarding mechanism • (Frame Relay, ATM, MPLS, …) ! ! ingress egress Label-switched
 ! core We’ll borrow: • ! Label-switched core: fixed-width, exact-match • lookups map easily into large forwarding tables
 Opaque labels: not assoc to physical endpoint in n/w • 5 Our solution: Shadow MACs Opaque forwarding label: Destination MAC address • Fast, cheap and large fwd’ing tables already in switch! • OpenFlow flow mods on ingress/egress guide onto paths
 • 
 MAC
 
 ACTION DST 
 B1 route 1. Ingress switch assigns
 B1 -> B
 
 B1 labels to packets out: port 
 A 
 B2 route B2 -> B
 ingress egress B2 out: port 
 MAC
 
 MAC
 PORT
 3. Egress switch
 ACTION 2. Core fwd’s on labels SRC DST DST rewrites MAC B 
 B -> B1
 address A B 80 out: port B -> B2
 A B * out: port 6 Shadow MACs: Rerouting Opaque labels: no physical host → preinstall routes • Ingress guiding: Changing routes now an atomic action!
 • 
 1. Controller preinstalls four routes from A to B, Ctlr MAC
 
 each with own shadow MAC address ACTION DST B1 -> B
 
 B1 out: port B2 -> B
 
 B2 out: port B1 B3 -> B
 
 B3 out: port B2 B4 -> B
 
 B4 out: port A ingress egress 2. Controller also
 
 B3 preinstalls rewrite
 
 rules on egress B B4 7 Shadow MACs: Rerouting Opaque labels: no physical host → preinstall routes • Ingress guiding: Changing routes now an atomic action!
 • 
 1. Controller preinstalls four routes from A to B, Ctlr MAC
 
 each with own shadow MAC address ACTION DST B1 -> B
 
 B1 out: port B2 -> B
 
 B2 out: port B1 B3 -> B
 
 B3 out: port B2 B4 -> B
 
 B4 out: port A ingress egress 2. Controller also
 
 B3 preinstalls rewrite
 
 rules on egress B B4 8 Shadow MACs: Rerouting Opaque labels: no physical host → preinstall routes • Ingress guiding: Changing routes now an atomic action!
 • 
 1. Single flow mod to ingress switch
 MAC
 ACTION Ctlr DST 
 switches paths B1 -> B
 B1 out: port 
 MAC
 MAC
 ACTION B2 -> B
 SRC DST B2 out: port 
 B -> B3
 A B B3 -> B
 out: green B3 out: port B1 
 B4 -> B
 B4 B2 out: port 
 A B ingress egress 
 B3 
 2. Traffic immediately switches
 to green route B4 9 Benefits • Controller guides pkts onto intelligently selected paths • Load balancing, link fail-over, route via middleboxes, differentiated services, … • Decouples network edge from core • Consistent n/w updates, fast rerouting, multi-pathing, … • Maps fine-grained matching to fixed destination-based rules • Pushes TCAM rules to FDB, limits TCAM usage in core • Implementable today! 10