Fabric: A Retrospective on Evolving SDN Presented by: Tarek Elgamal

Outline What is ideal Network design ? What are the SDN Limitations ? What is Multiprotocol label switching (MPLS) ? How the MPLS design address the SDN limitations ? How can we extend SDN to support MPLS ideas ?

Ideal Network Design Ideal Hardware: Simple: Hardware should be inexpensive to build and operate Vendor-neutral: Users easily switch between hardware vendors without complex upgrades Future-proof: Users should not need to upgrade hardware unnecessarily Ideal Software Flexibility: supports configuration for a wide variety of requirements (e.g., isolation, security, traffic engineering, routing algorithms) “Today’s Internet does not satisfy any!” MPLS SDN

Ideal Network Design Host-Network Interface Operator-Network Interface Packet-Switch Interface Host-Network Interface: How the hosts inform the network of their requirements Operator-Network Interface How operator (ISP) controls the network infrastructure Packet-switch Interface What fields the switch needs from the packet to forward it. Ideal network design should separate between the three SDN MPLS

Multi-protocol Label Switching (MPLS) Data packets are assigned labels that correspond with paths through the network instead of end points Routers follow the predefined labelled path Routers propagate dynamic changes in the network and paths are updated accordingly IP Packet Ingress router receives and labels packet IP PacketLabel IP PacketLabel IP Packet Eggress router Removes label delivers packet Switching router: Only does switching based on the label

Advantages of MPLS Distinction between network edge and network core Core hardware become much simpler MPLS labels decoupled from host protocol (e.g. IPv4) Distinguishes between Host — Network and Packet— Switch Interfaces IP Packet Ingress router receives and labels packet IP PacketLabel IP PacketLabel IP Packet Eggress router Removes label delivers packet

Network Interfaces Host-Network Interface Operator-Network Interface Packet-Switch Interface Host-Network Interface: How the hosts inform the network of their requirements Operator-Network Interface How operator controls the network infrastructure Packet-switch Interface What fields the switch needs from the packet to forward it. Ideal network design should separate between the three SDN Operator-Network: OpenFlow Host-Network: IPv4 Packet-Switch: IPv4 MPLS Host-Network: IPv4 Packet-Switch: MPLS (packet routing through label only) Same Extended SDN Operator-Network: OpenFlow Host-Network: IPv4 Packet-Switch: MPLS ideas

SDN vs MPLS Ideal Hardware: Simple: Hardware should be inexpensive to build and operate SDN forward on IPv4 headers (100s of bits) MPLS forwards on the label only (10s of bits) Vendor-neutral: Users easily switch between hardware vendors without complex upgrades SDN uses today’s routers which has rich set of features MPLS routers only need to forward packets on a predefined path (minimal set of features would suffice) Future-proof: Users should not need to upgrade hardware unnecessarily SDN has to deal with host’s protocol (e.g. IPv4) MPLS decouples edge protocol from core protocol (IPv4  IPv6 will not affect core of the network)

Extended SDN Network components: Host, Edge, Fabric (switch for basic packet transport only) Two logical controllers (edge and fabric controllers) Network Interfaces: Host – Network : Ingress edge switch Operator– Network : Edge controller Packet– Switch: Fabric elements and controller

Extended SDN - Design Principles Separation of forwarding Minimal set of forwarding primitives Separation of control Two separate roles: Fabric transports packet Switch provides security, Mobility, and other services The main principle is to allow edge and core technologies to evolve separately

Fabric Component Interconnects the edge as fast and cheaply as possible. Supports any number of edge designs (i.e., different addressing schemes and policy models) Supports point-to-point and point-to-multipoint communication Have packet-dropping mechanism under congestion Should not support filtering,isolation, stateful flow tracking

Fabric Path Setup Two suggested approaches Forwarding on pre-calculated paths Reduces provisioning overhead, if both the edge and the fabric are part of the same administrative domain Explicit provisioning of the path by the provider (ingress and egress switches exchange control messages to establish path with specific requirements, then packet transfer starts) Used with customer-provider relationship

Mapping between Edge/Fabric Addresses Two suggested approaches Address translation: edge addresses are replaced with fabric internal addresses, translated back to edge addresses at the destination Downside: Couples the edge and core addressing schemes Encapsulation: encapsulated with another header that carries the Fabric internal addresses More general and decouples addressing schemes  IP Header Fabric Header Fabric Header

Discussion Can SDN with OpenFlow be used to implement MPLS instead of changing the whole architecture ? What are some suggested changes to OpenFlow to adopt this architecture ? Do you think simplifying the hardware infrastructure achieves vendor-neutrality ?