Thoughts on Potential OF 1.1
Features
Martin Casado, Brandon Heller, Glen
Gibb, Rajiv Ramanathan, Leon
Poutievski, Edward Crabbe, You
Rough Schedule
• This week:
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–
–
–
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
Perhaps a generalized set of
actions on flow
•
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
Multipath Implementation Example
(1)
Explicit Group Definition
(1)
Implicit 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?