Thoughts on Potential OF 1.1 Features Martin Casado, Brandon Heller, Glen Gibb, Rajiv Ramanathan, Leon Poutievski, Edward Crabbe, You

Rough Schedule This week: – TTL decrement – LPM on Non-IP fields / Non-contiguous masks – Multipath – Multiple Tables Next week – Tunnels and Tags – Misc Openflow Changes uint32 for port speeds and port ID space Ability to add and delete ports dynamically – Multiple tables Following Weeks – Multiple Tables…

TTL Decrement Required for loop prevention, diagnostics Generalized vs proto specific implementation: – Perception is not a great deal of demand for generalized field decrement – Required for IP, MPLS, various diagnostic tools (traceroute etc) protocol changes for IP/MPLS field decrement: – Match on TTL – TTL decrement action – Action on ttl 0 would generally be to forward to controller Chksum computation implied

LPM on Non-IP Required for some proposed DC architectures (eg: Portland) Perhaps also allow Non-contiguous masks? (some odd use cases such as overloading IPv4 addresses in MAC for in DC src routing) Perhaps just non-contiguous IP and MAC fields How to implement in backwards compatible manner

Multipath Simple use case: load balance packets across k parallel links based on routing protocol decision Flows are mapped to link based on results of n tuple hash (typically across src/dst IP, src/dst TCP port or similar) to avoid flow reordering

Multipath Implementation based on concept of a multipath ‘group’ Each group represents a set of action buckets, one of which is chosen for each packet. – For LAG: bucket  port – For L3 ECMP: bucket  port, MAC rewrite Group existence and membership established dynamically via OF protocol. This decouples config protocol from routing decisions / time scales. Group management implemented on the controller – Eg: remove/add group on port down/up events when some capacity threshold is reached The following operations would be required, whether explicit of implicit: – Create/delete multipath group – Add/delete port from group – Query group membership Perhaps a generalized set of actions on flow

Multipath Implementation Example (1)Implicit Group Definition (1)Explicit Group Definition

Implicit VS Explicit Groups Implicit Advantages: – simpler for developer no need to consider two messages, message order or consistency Explicit Advantages: – simpler, dumber switch – Provides level of indirection, more efficient

Multiple Tables Single table leads to combinatoric explosion in both table size and number of flow mod messages eg: from any, to any, tcp port 179, count, drop Each action must be expanded across every re;evant address in table, resulting in cartesian product of fields matched against

Multiple Tables Model is based on pipeline register (lookup scratchpad) – Is used to track progress of lookup through pipeline Model requires addition of two new actions: – Resubmit: resubmit packet for another lookup – Write: write a value into the register. Register value should increase monotonically to prevent loops. Model also requires ability to match on register

Multiple Tables Just A Few of the Open Issues Conflicts between actions in both parallel and serial pipelines – HAL to determine conflict or programmers responsibility? – Override / accumulate action flag ? table type conflicts - send a reject message? table overflow - send a reject message? exposure of parallel tables – is there any use case of non serializable action?